draft-ietf-idr-bgp4-18.txt   draft-ietf-idr-bgp4-19.txt 
Network Working Group Y. Rekhter Network Working Group Y. Rekhter
INTERNET DRAFT Juniper Networks INTERNET DRAFT Juniper Networks
T. Li T. Li
Procket Networks, Inc. Procket Networks, Inc.
S. Hares S. Hares
NextHop Technologies, Inc. NextHop Technologies, Inc.
Editors Editors
A Border Gateway Protocol 4 (BGP-4) A Border Gateway Protocol 4 (BGP-4)
<draft-ietf-idr-bgp4-18.txt> <draft-ietf-idr-bgp4-19.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 2, line 5 skipping to change at page 2, line 5
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Specification of Requirements Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119]. document are to be interpreted as described in RFC2119 [RFC2119].
Table of Contents TTaabbllee ooff CCoonntteennttss
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Definition of commonly used terms . . . . . . . . . . . . . . 4 1. Definition of commonly used terms . . . . . . . . . . . . . . 4
2. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 2. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
3. Summary of Operation . . . . . . . . . . . . . . . . . . . . . 7 3. Summary of Operation . . . . . . . . . . . . . . . . . . . . . 7
3.1 Routes: Advertisement and Storage . . . . . . . . . . . . . . 9 3.1 Routes: Advertisement and Storage . . . . . . . . . . . . . . 9
3.2 Routing Information Bases . . . . . . . . . . . . . . . . . . 10 3.2 Routing Information Bases . . . . . . . . . . . . . . . . . . 10
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 11 4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 11
4.1 Message Header Format . . . . . . . . . . . . . . . . . . . . 11 4.1 Message Header Format . . . . . . . . . . . . . . . . . . . . 11
4.2 OPEN Message Format . . . . . . . . . . . . . . . . . . . . . 12 4.2 OPEN Message Format . . . . . . . . . . . . . . . . . . . . . 12
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Appendix D. Comparison with RFC 1105 . . . . . . . . . . . . . . 75 Appendix D. Comparison with RFC 1105 . . . . . . . . . . . . . . 75
Appendix E. TCP options that may be used with BGP . . . . . . . . 76 Appendix E. TCP options that may be used with BGP . . . . . . . . 76
Appendix F. Implementation Recommendations . . . . . . . . . . . 76 Appendix F. Implementation Recommendations . . . . . . . . . . . 76
Appendix F.1 Multiple Networks Per Message . . . . . . . . . . . 76 Appendix F.1 Multiple Networks Per Message . . . . . . . . . . . 76
Appendix F.2 Reducing route flapping . . . . . . . . . . . . . . 77 Appendix F.2 Reducing route flapping . . . . . . . . . . . . . . 77
Appendix F.3 Path attribute ordering . . . . . . . . . . . . . . 77 Appendix F.3 Path attribute ordering . . . . . . . . . . . . . . 77
Appendix F.4 AS_SET sorting . . . . . . . . . . . . . . . . . . . 77 Appendix F.4 AS_SET sorting . . . . . . . . . . . . . . . . . . . 77
Appendix F.5 Control over version negotiation . . . . . . . . . . 78 Appendix F.5 Control over version negotiation . . . . . . . . . . 78
Appendix F.6 Complex AS_PATH aggregation . . . . . . . . . . . . 78 Appendix F.6 Complex AS_PATH aggregation . . . . . . . . . . . . 78
Security Considerations . . . . . . . . . . . . . . . . . . . . . 79 Security Considerations . . . . . . . . . . . . . . . . . . . . . 79
IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 79
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Authors Information . . . . . . . . . . . . . . . . . . . . . . . 80 Authors Information . . . . . . . . . . . . . . . . . . . . . . . 80
Abstract Abstract
The Border Gateway Protocol (BGP) is an inter-Autonomous System rout- The Border Gateway Protocol (BGP) is an inter-Autonomous System rout-
ing protocol. ing protocol.
The primary function of a BGP speaking system is to exchange network The primary function of a BGP speaking system is to exchange network
reachability information with other BGP systems. This network reacha- reachability information with other BGP systems. This network reacha-
skipping to change at page 7, line 34 skipping to change at page 7, line 34
tion is sufficient to construct a graph of AS connectivity from which tion is sufficient to construct a graph of AS connectivity from which
routing loops may be pruned and some policy decisions at the AS level routing loops may be pruned and some policy decisions at the AS level
may be enforced. may be enforced.
In the context of this document we assume that a BGP speaker adver- In the context of this document we assume that a BGP speaker adver-
tises to its peers only those routes that it itself uses (in this tises to its peers only those routes that it itself uses (in this
context a BGP speaker is said to "use" a BGP route if it is the most context a BGP speaker is said to "use" a BGP route if it is the most
preferred BGP route and is used in forwarding). All other cases are preferred BGP route and is used in forwarding). All other cases are
outside the scope of this document. outside the scope of this document.
In the context of this document the term "IP address" refers to an IP
Version 4 address [RFC791].
Routing information exchanged via BGP supports only the destination- Routing information exchanged via BGP supports only the destination-
based forwarding paradigm, which assumes that a router forwards a based forwarding paradigm, which assumes that a router forwards a
packet based solely on the destination address carried in the IP packet based solely on the destination address carried in the IP
header of the packet. This, in turn, reflects the set of policy deci- header of the packet. This, in turn, reflects the set of policy deci-
sions that can (and can not) be enforced using BGP. Note that some sions that can (and can not) be enforced using BGP. Note that some
policies can not be supported by the destination-based forwarding policies can not be supported by the destination-based forwarding
paradigm, and thus require techniques such as source routing (aka paradigm, and thus require techniques such as source routing (aka
explicit routing) to be enforced. Such policies can not be enforced explicit routing) to be enforced. Such policies can not be enforced
using BGP either. For example, BGP does not enable one AS to send using BGP either. For example, BGP does not enable one AS to send
traffic to a neighboring AS for forwarding to some destination traffic to a neighboring AS for forwarding to some destination
(reachable through but) beyond that neighboring AS intending that the (reachable through but) beyond that neighboring AS intending that the
traffic take a different route to that taken by the traffic originat- traffic take a different route to that taken by the traffic originat-
ing in the neighboring AS (for that same destination). On the other ing in the neighboring AS (for that same destination). On the other
hand, BGP can support any policy conforming to the destination-based hand, BGP can support any policy conforming to the destination-based
forwarding paradigm. forwarding paradigm.
A more complete discussion of what policies can and can not be
enforced with BGP is outside the scope of this document (but refer to
the companion document discussing BGP usage [RFC1772]).
BGP-4 provides a new set of mechanisms for supporting Classless BGP-4 provides a new set of mechanisms for supporting Classless
Inter-Domain Routing (CIDR) [RFC1518, RFC1519]. These mechanisms Inter-Domain Routing (CIDR) [RFC1518, RFC1519]. These mechanisms
include support for advertising a set of destinations as an IP prefix include support for advertising a set of destinations as an IP prefix
and eliminating the concept of network "class" within BGP. BGP-4 and eliminating the concept of network "class" within BGP. BGP-4
also introduces mechanisms which allow aggregation of routes, includ- also introduces mechanisms which allow aggregation of routes, includ-
ing aggregation of AS paths. ing aggregation of AS paths.
This document uses the term `Autonomous System' (AS) throughout. The This document uses the term `Autonomous System' (AS) throughout. The
classic definition of an Autonomous System is a set of routers under classic definition of an Autonomous System is a set of routers under
a single technical administration, using an interior gateway protocol a single technical administration, using an interior gateway protocol
(IGP) and common metrics to determine how to route packets within the (IGP) and common metrics to determine how to route packets within the
AS, and using an inter-AS routing protocol to determine how to route AS, and using an inter-AS routing protocol to determine how to route
packets to other ASs. Since this classic definition was developed, it packets to other ASs. Since this classic definition was developed, it
has become common for a single AS to use several IGPs and sometimes has become common for a single AS to use several IGPs and sometimes
several sets of metrics within an AS. The use of the term Autonomous several sets of metrics within an AS. The use of the term Autonomous
System here stresses the fact that, even when multiple IGPs and met- System here stresses the fact that, even when multiple IGPs and met-
rics are used, the administration of an AS appears to other ASs to rics are used, the administration of an AS appears to other ASs to
have a single coherent interior routing plan and presents a consis- have a single coherent interior routing plan and presents a consis-
tent picture of what destinations are reachable through it. tent picture of what destinations are reachable through it.
The planned use of BGP in the Internet environment, including such
issues as topology, the interaction between BGP and IGPs, and the
enforcement of routing policy rules is presented in a companion docu-
ment [RFC1772]. This document is the first of a series of documents
planned to explore various aspects of BGP application.
BGP uses TCP [RFC793] as its transport protocol. This eliminates the BGP uses TCP [RFC793] as its transport protocol. This eliminates the
need to implement explicit update fragmentation, retransmission, need to implement explicit update fragmentation, retransmission,
acknowledgment, and sequencing. BGP listens on TCP port 179. Any acknowledgment, and sequencing. BGP listens on TCP port 179. The
authentication scheme used by TCP (e.g., RFC2385 [RFC2385]) may be error notification mechanism used in BGP assumes that TCP supports a
used. The error notification mechanism used in BGP assumes that TCP "graceful" close, i.e., that all outstanding data will be delivered
supports a "graceful" close, i.e., that all outstanding data will be before the connection is closed.
delivered before the connection is closed.
Two systems form a TCP connection between one another. They exchange Two systems form a TCP connection between one another. They exchange
messages to open and confirm the connection parameters. messages to open and confirm the connection parameters.
The initial data flow is the portion of the BGP routing table that is The initial data flow is the portion of the BGP routing table that is
allowed by the export policy, called the Adj-Ribs-Out (see 3.2). allowed by the export policy, called the Adj-Ribs-Out (see 3.2).
Incremental updates are sent as the routing tables change. BGP does Incremental updates are sent as the routing tables change. BGP does
not require periodic refresh of the routing table. To allow local not require periodic refresh of the routing table. To allow local
policy changes to have the correct effect without resetting any BGP policy changes to have the correct effect without resetting any BGP
connections, a BGP speaker SHOULD either (a) retain the current ver- connections, a BGP speaker SHOULD either (a) retain the current ver-
sion of the routes advertised to it by all of its peers for the dura- sion of the routes advertised to it by all of its peers for the dura-
tion of the connection, or (b) make use of the Route Refresh tion of the connection, or (b) make use of the Route Refresh exten-
extension [RFC2918]. sion [RFC2918].
KEEPALIVE messages may be sent periodically to ensure the liveness of KEEPALIVE messages may be sent periodically to ensure the liveness of
the connection. NOTIFICATION messages are sent in response to errors the connection. NOTIFICATION messages are sent in response to errors
or special conditions. If a connection encounters an error condition, or special conditions. If a connection encounters an error condition,
a NOTIFICATION message is sent and the connection is closed. a NOTIFICATION message is sent and the connection is closed.
The hosts executing BGP need not be routers. A non-routing host
could exchange routing information with routers via EGP [RFC904] or
even an interior routing protocol. That non-routing host could then
use BGP to exchange routing information with a border router in
another Autonomous System. The implications and applications of this
architecture are for further study.
A peer in a different AS is referred to as an external peer, while a A peer in a different AS is referred to as an external peer, while a
peer in the same AS may be described as an internal peer. Internal peer in the same AS is referred to as an internal peer. Internal BGP
BGP and external BGP are commonly abbreviated IBGP and EBGP. and external BGP are commonly abbreviated IBGP and EBGP.
If a particular AS has multiple BGP speakers and is providing transit If a particular AS has multiple BGP speakers and is providing transit
service for other ASs, then care must be taken to ensure a consistent service for other ASs, then care must be taken to ensure a consistent
view of routing within the AS. A consistent view of the interior view of routing within the AS. A consistent view of the interior
routes of the AS is provided by the IGP used within the AS. For the routes of the AS is provided by the IGP used within the AS. For the
purpose of this document, it is assumed that a consistent view of the purpose of this document, it is assumed that a consistent view of the
routes exterior to the AS is provided by having all BGP speakers routes exterior to the AS is provided by having all BGP speakers
within the AS maintain IBGP with each other. Care must be taken to within the AS maintain IBGP with each other. Care must be taken to
ensure that the interior routers have all been updated with transit ensure that the interior routers have all been updated with transit
information before the BGP speakers announce to other ASs that tran- information before the BGP speakers announce to other ASs that tran-
sit service is being provided. sit service is being provided.
This document specifies the base behavior of the BGP protocol. This
behavior can and is modified by extention specifications. When the
protocol is extended the new behavior is fully documented in the
extention specifications.
3.1 Routes: Advertisement and Storage 3.1 Routes: Advertisement and Storage
For the purpose of this protocol, a route is defined as a unit of For the purpose of this protocol, a route is defined as a unit of
information that pairs a set of destinations with the attributes of a information that pairs a set of destinations with the attributes of a
path to those destinations. The set of destinations are systems whose path to those destinations. The set of destinations are systems whose
IP addresses are contained in one IP address prefix carried in the IP addresses are contained in one IP address prefix carried in the
Network Layer Reachability Information (NLRI) field of an UPDATE mes- Network Layer Reachability Information (NLRI) field of an UPDATE mes-
sage, and the path is the information reported in the path attributes sage, and the path is the information reported in the path attributes
field of the same UPDATE message. field of the same UPDATE message.
Routes are advertised between BGP speakers in UPDATE messages. Mul- Routes are advertised between BGP speakers in UPDATE messages. Mul-
tiple routes that have the same path attributes can be advertised in tiple routes that have the same path attributes can be advertised in
a single UPDATE message by including multiple prefixes in the NLRI a single UPDATE message by including multiple prefixes in the NLRI
field of the UPDATE message. field of the UPDATE message.
Routes are stored in the Routing Information Bases (RIBs): namely, Routes are stored in the Routing Information Bases (RIBs): namely,
the Adj-RIBs-In, the Loc-RIB, and the Adj-RIBs-Out, as described in the Adj-RIBs-In, the Loc-RIB, and the Adj-RIBs-Out, as described in
Section 3.2. Section 3.2.
If a BGP speaker chooses to advertise the route, it may add to or If a BGP speaker chooses to advertise the route, it MAY add to or
modify the path attributes of the route before advertising it to a modify the path attributes of the route before advertising it to a
peer. peer.
BGP provides mechanisms by which a BGP speaker can inform its peer BGP provides mechanisms by which a BGP speaker can inform its peer
that a previously advertised route is no longer available for use. that a previously advertised route is no longer available for use.
There are three methods by which a given BGP speaker can indicate There are three methods by which a given BGP speaker can indicate
that a route has been withdrawn from service: that a route has been withdrawn from service:
a) the IP prefix that expresses the destination for a previously a) the IP prefix that expresses the destination for a previously
advertised route can be advertised in the WITHDRAWN ROUTES field advertised route can be advertised in the WITHDRAWN ROUTES field
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a) Adj-RIBs-In: The Adj-RIBs-In store routing information that has a) Adj-RIBs-In: The Adj-RIBs-In store routing information that has
been learned from inbound UPDATE messages received from other BGP been learned from inbound UPDATE messages received from other BGP
speakers. Their contents represent routes that are available as an speakers. Their contents represent routes that are available as an
input to the Decision Process. input to the Decision Process.
b) Loc-RIB: The Loc-RIB contains the local routing information b) Loc-RIB: The Loc-RIB contains the local routing information
that the BGP speaker has selected by applying its local policies that the BGP speaker has selected by applying its local policies
to the routing information contained in its Adj-RIBs-In. These are to the routing information contained in its Adj-RIBs-In. These are
the routes that will be used by the local BGP speaker. The next the routes that will be used by the local BGP speaker. The next
hop for each of these routes must be resolvable via the local BGP hop for each of these routes MUST be resolvable via the local BGP
speaker's Routing Table. speaker's Routing Table.
c) Adj-RIBs-Out: The Adj-RIBs-Out store the information that the c) Adj-RIBs-Out: The Adj-RIBs-Out store the information that the
local BGP speaker has selected for advertisement to its peers. The local BGP speaker has selected for advertisement to its peers. The
routing information stored in the Adj-RIBs-Out will be carried in routing information stored in the Adj-RIBs-Out will be carried in
the local BGP speaker's UPDATE messages and advertised to its the local BGP speaker's UPDATE messages and advertised to its
peers. peers.
In summary, the Adj-RIBs-In contain unprocessed routing information In summary, the Adj-RIBs-In contain unprocessed routing information
that has been advertised to the local BGP speaker by its peers; the that has been advertised to the local BGP speaker by its peers; the
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for advertisement to specific peers by means of the local speaker's for advertisement to specific peers by means of the local speaker's
UPDATE messages. UPDATE messages.
Although the conceptual model distinguishes between Adj-RIBs-In, Loc- Although the conceptual model distinguishes between Adj-RIBs-In, Loc-
RIB, and Adj-RIBs-Out, this neither implies nor requires that an RIB, and Adj-RIBs-Out, this neither implies nor requires that an
implementation must maintain three separate copies of the routing implementation must maintain three separate copies of the routing
information. The choice of implementation (for example, 3 copies of information. The choice of implementation (for example, 3 copies of
the information vs 1 copy with pointers) is not constrained by the the information vs 1 copy with pointers) is not constrained by the
protocol. protocol.
Routing information that the router uses to forward packets (or to Routing information that the BGP speaker uses to forward packets (or
construct the forwarding table that is used for packet forwarding) is to construct the forwarding table that is used for packet forwarding)
maintained in the Routing Table. The Routing Table accumulates routes is maintained in the Routing Table. The Routing Table accumulates
to directly connected networks, static routes, routes learned from routes to directly connected networks, static routes, routes learned
the IGP protocols, and routes learned from BGP. Whether or not a from the IGP protocols, and routes learned from BGP. Whether or not
specific BGP route should be installed in the Routing Table, and a specific BGP route should be installed in the Routing Table, and
whether a BGP route should override a route to the same destination whether a BGP route should override a route to the same destination
installed by another source is a local policy decision, not specified installed by another source is a local policy decision, not specified
in this document. Besides actual packet forwarding, the Routing Table in this document. Besides actual packet forwarding, the Routing Table
is used for resolution of the next-hop addresses specified in BGP is used for resolution of the next-hop addresses specified in BGP
updates (see Section 5.1.3). updates (see Section 5.1.3).
4. Message Formats 4. Message Formats
This section describes message formats used by BGP. This section describes message formats used by BGP.
BGP messages are sent over a TCP connection. A message is processed BGP messages are sent over a TCP connection. A message is processed
only after it is entirely received. The maximum message size is 4096 only after it is entirely received. The maximum message size is 4096
octets. All implementations are required to support this maximum mes- octets. All implementations are required to support this maximum mes-
sage size. The smallest message that may be sent consists of a BGP sage size. The smallest message that may be sent consists of a BGP
header without a data portion, or 19 octets. header without a data portion, or 19 octets.
All multi-octet fields are in network byte order.
4.1 Message Header Format 4.1 Message Header Format
Each message has a fixed-size header. There may or may not be a data Each message has a fixed-size header. There may or may not be a data
portion following the header, depending on the message type. The lay- portion following the header, depending on the message type. The lay-
out of these fields is shown below: out of these fields is shown below:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
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Marker: Marker:
This 16-octet field is included for compatibility; it MUST be This 16-octet field is included for compatibility; it MUST be
set to all ones. set to all ones.
Length: Length:
This 2-octet unsigned integer indicates the total length of the This 2-octet unsigned integer indicates the total length of the
message, including the header, in octets. Thus, e.g., it allows message, including the header, in octets. Thus, e.g., it allows
one to locate in the TCP stream the (Marker field of the) next one to locate in the TCP stream the (Marker field of the) next
message. The value of the Length field must always be at least message. The value of the Length field MUST always be at least
19 and no greater than 4096, and may be further constrained, 19 and no greater than 4096, and MAY be further constrained,
depending on the message type. No "padding" of extra data after depending on the message type. No "padding" of extra data after
the message is allowed, so the Length field must have the the message is allowed, so the Length field MUST have the
smallest value required given the rest of the message. smallest value required given the rest of the message.
Type: Type:
This 1-octet unsigned integer indicates the type code of the This 1-octet unsigned integer indicates the type code of the
message. This document defines the following type codes: message. This document defines the following type codes:
1 - OPEN 1 - OPEN
2 - UPDATE 2 - UPDATE
3 - NOTIFICATION 3 - NOTIFICATION
4 - KEEPALIVE 4 - KEEPALIVE
[RFC2918] defines one more type code. [RFC2918] defines one more type code.
4.2 OPEN Message Format 4.2 OPEN Message Format
After a TCP is established, the first message sent by each side is an After a TCP is established, the first message sent by each side is an
OPEN message. If the OPEN message is acceptable, a KEEPALIVE message OPEN message. If the OPEN message is acceptable, a KEEPALIVE message
confirming the OPEN is sent back. Once the OPEN is confirmed, UPDATE, confirming the OPEN is sent back.
KEEPALIVE, and NOTIFICATION messages may be exchanged.
In addition to the fixed-size BGP header, the OPEN message contains In addition to the fixed-size BGP header, the OPEN message contains
the following fields: the following fields:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Version | | Version |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Autonomous System | | My Autonomous System |
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number of the sender. number of the sender.
Hold Time: Hold Time:
This 2-octet unsigned integer indicates the number of seconds This 2-octet unsigned integer indicates the number of seconds
that the sender proposes for the value of the Hold Timer. Upon that the sender proposes for the value of the Hold Timer. Upon
receipt of an OPEN message, a BGP speaker MUST calculate the receipt of an OPEN message, a BGP speaker MUST calculate the
value of the Hold Timer by using the smaller of its configured value of the Hold Timer by using the smaller of its configured
Hold Time and the Hold Time received in the OPEN message. The Hold Time and the Hold Time received in the OPEN message. The
Hold Time MUST be either zero or at least three seconds. An Hold Time MUST be either zero or at least three seconds. An
implementation may reject connections on the basis of the Hold implementation MAY reject connections on the basis of the Hold
Time. The calculated value indicates the maximum number of Time. The calculated value indicates the maximum number of
seconds that may elapse between the receipt of successive seconds that may elapse between the receipt of successive
KEEPALIVE, and/or UPDATE messages by the sender. KEEPALIVE, and/or UPDATE messages by the sender.
BGP Identifier: BGP Identifier:
This 4-octet unsigned integer indicates the BGP Identifier of This 4-octet unsigned integer indicates the BGP Identifier of
the sender. A given BGP speaker sets the value of its BGP Iden- the sender. A given BGP speaker sets the value of its BGP Iden-
tifier to an IP address assigned to that BGP speaker. The tifier to an IP address assigned to that BGP speaker. The
value of the BGP Identifier is determined on startup and is the value of the BGP Identifier is determined on startup and is the
same for every local interface and every BGP peer. same for every local interface and every BGP peer.
Optional Parameters Length: Optional Parameters Length:
This 1-octet unsigned integer indicates the total length of the This 1-octet unsigned integer indicates the total length of the
Optional Parameters field in octets. If the value of this field Optional Parameters field in octets. If the value of this field
is zero, no Optional Parameters are present. is zero, no Optional Parameters are present.
Optional Parameters: Optional Parameters:
This field may contain a list of optional parameters, where This field contains a list of optional parameters, where each
each parameter is encoded as a <Parameter Type, Parameter parameter is encoded as a <Parameter Type, Parameter Length,
Length, Parameter Value> triplet. Parameter Value> triplet.
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
| Parm. Type | Parm. Length | Parameter Value (variable) | Parm. Type | Parm. Length | Parameter Value (variable)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
Parameter Type is a one octet field that unambiguously identi- Parameter Type is a one octet field that unambiguously identi-
fies individual parameters. Parameter Length is a one octet fies individual parameters. Parameter Length is a one octet
field that contains the length of the Parameter Value field in field that contains the length of the Parameter Value field in
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4.3 UPDATE Message Format 4.3 UPDATE Message Format
UPDATE messages are used to transfer routing information between BGP UPDATE messages are used to transfer routing information between BGP
peers. The information in the UPDATE message can be used to construct peers. The information in the UPDATE message can be used to construct
a graph describing the relationships of the various Autonomous Sys- a graph describing the relationships of the various Autonomous Sys-
tems. By applying rules to be discussed, routing information loops tems. By applying rules to be discussed, routing information loops
and some other anomalies may be detected and removed from inter-AS and some other anomalies may be detected and removed from inter-AS
routing. routing.
An UPDATE message is used to advertise feasible routes sharing common An UPDATE message is used to advertise feasible routes sharing common
path attribute to a peer, or to withdraw multiple unfeasible routes path attributes to a peer, or to withdraw multiple unfeasible routes
from service (see 3.1). An UPDATE message may simultaneously adver- from service (see 3.1). An UPDATE message MAY simultaneously adver-
tise a feasible route and withdraw multiple unfeasible routes from tise a feasible route and withdraw multiple unfeasible routes from
service. The UPDATE message always includes the fixed-size BGP service. The UPDATE message always includes the fixed-size BGP
header, and also includes the other fields as shown below (note, some header, and also includes the other fields as shown below (note, some
of the shown fields may not be present in every UPDATE message): of the shown fields may not be present in every UPDATE message):
+-----------------------------------------------------+ +-----------------------------------------------------+
| Withdrawn Routes Length (2 octets) | | Withdrawn Routes Length (2 octets) |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Withdrawn Routes (variable) | | Withdrawn Routes (variable) |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Total Path Attribute Length (2 octets) | | Total Path Attribute Length (2 octets) |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Path Attributes (variable) | | Path Attributes (variable) |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Network Layer Reachability Information (variable) | | Network Layer Reachability Information (variable) |
+-----------------------------------------------------+ +-----------------------------------------------------+
Withdrawn Routes Length: Withdrawn Routes Length:
This 2-octets unsigned integer indicates the total length of This 2-octets unsigned integer indicates the total length of
the Withdrawn Routes field in octets. Its value must allow the the Withdrawn Routes field in octets. Its value allows the
length of the Network Layer Reachability Information field to length of the Network Layer Reachability Information field to
be determined as specified below. be determined as specified below.
A value of 0 indicates that no routes are being withdrawn from A value of 0 indicates that no routes are being withdrawn from
service, and that the WITHDRAWN ROUTES field is not present in service, and that the WITHDRAWN ROUTES field is not present in
this UPDATE message. this UPDATE message.
Withdrawn Routes: Withdrawn Routes:
This is a variable length field that contains a list of IP This is a variable length field that contains a list of IP
skipping to change at page 16, line 15 skipping to change at page 16, line 13
a) Length: a) Length:
The Length field indicates the length in bits of the IP The Length field indicates the length in bits of the IP
address prefix. A length of zero indicates a prefix that address prefix. A length of zero indicates a prefix that
matches all IP addresses (with prefix, itself, of zero matches all IP addresses (with prefix, itself, of zero
octets). octets).
b) Prefix: b) Prefix:
The Prefix field contains an IP address prefix followed by The Prefix field contains an IP address prefix followed by
enough trailing bits to make the end of the field fall on an the minimum number of trailing bits needed to make the end
octet boundary. Note that the value of trailing bits is of the field fall on an octet boundary. Note that the value
irrelevant. of trailing bits is irrelevant.
Total Path Attribute Length: Total Path Attribute Length:
This 2-octet unsigned integer indicates the total length of the This 2-octet unsigned integer indicates the total length of the
Path Attributes field in octets. Its value must allow the Path Attributes field in octets. Its value allows the length of
length of the Network Layer Reachability field to be determined the Network Layer Reachability field to be determined as speci-
as specified below. fied below.
A value of 0 indicates that no Network Layer Reachability A value of 0 indicates that no Network Layer Reachability
Information field is present in this UPDATE message. Information field is present in this UPDATE message.
Path Attributes: Path Attributes:
A variable length sequence of path attributes is present in A variable length sequence of path attributes is present in
every UPDATE message, except for an UPDATE message that carries every UPDATE message, except for an UPDATE message that carries
only the withdrawn routes. Each path attribute is a triple only the withdrawn routes. Each path attribute is a triple
<attribute type, attribute length, attribute value> of variable <attribute type, attribute length, attribute value> of variable
skipping to change at page 17, line 5 skipping to change at page 16, line 52
| Attr. Flags |Attr. Type Code| | Attr. Flags |Attr. Type Code|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The high-order bit (bit 0) of the Attribute Flags octet is the The high-order bit (bit 0) of the Attribute Flags octet is the
Optional bit. It defines whether the attribute is optional (if Optional bit. It defines whether the attribute is optional (if
set to 1) or well-known (if set to 0). set to 1) or well-known (if set to 0).
The second high-order bit (bit 1) of the Attribute Flags octet The second high-order bit (bit 1) of the Attribute Flags octet
is the Transitive bit. It defines whether an optional attribute is the Transitive bit. It defines whether an optional attribute
is transitive (if set to 1) or non-transitive (if set to 0). is transitive (if set to 1) or non-transitive (if set to 0).
For well-known attributes, the Transitive bit must be set to 1. For well-known attributes, the Transitive bit MUST be set to 1.
(See Section 5 for a discussion of transitive attributes.) (See Section 5 for a discussion of transitive attributes.)
The third high-order bit (bit 2) of the Attribute Flags octet The third high-order bit (bit 2) of the Attribute Flags octet
is the Partial bit. It defines whether the information con- is the Partial bit. It defines whether the information con-
tained in the optional transitive attribute is partial (if set tained in the optional transitive attribute is partial (if set
to 1) or complete (if set to 0). For well-known attributes and to 1) or complete (if set to 0). For well-known attributes and
for optional non-transitive attributes the Partial bit must be for optional non-transitive attributes the Partial bit MUST be
set to 0. set to 0.
The fourth high-order bit (bit 3) of the Attribute Flags octet The fourth high-order bit (bit 3) of the Attribute Flags octet
is the Extended Length bit. It defines whether the Attribute is the Extended Length bit. It defines whether the Attribute
Length is one octet (if set to 0) or two octets (if set to 1). Length is one octet (if set to 0) or two octets (if set to 1).
The lower-order four bits of the Attribute Flags octet are The lower-order four bits of the Attribute Flags octet are
unused. They must be zero when sent and must be ignored when unused. They MUST be zero when sent and MUST be ignored when
received. received.
The Attribute Type Code octet contains the Attribute Type Code. The Attribute Type Code octet contains the Attribute Type Code.
Currently defined Attribute Type Codes are discussed in Section Currently defined Attribute Type Codes are discussed in Section
5. 5.
If the Extended Length bit of the Attribute Flags octet is set If the Extended Length bit of the Attribute Flags octet is set
to 0, the third octet of the Path Attribute contains the length to 0, the third octet of the Path Attribute contains the length
of the attribute data in octets. of the attribute data in octets.
skipping to change at page 18, line 40 skipping to change at page 18, line 38
the number of ASs (not the number of octets) in the path the number of ASs (not the number of octets) in the path
segment value field. segment value field.
The path segment value field contains one or more AS num- The path segment value field contains one or more AS num-
bers, each encoded as a 2-octets long field. bers, each encoded as a 2-octets long field.
Usage of this attribute is defined in 5.1.2. Usage of this attribute is defined in 5.1.2.
c) NEXT_HOP (Type Code 3): c) NEXT_HOP (Type Code 3):
This is a well-known mandatory attribute that defines the IP This is a well-known mandatory attribute that defines the
address of the border router that should be used as the next (unicast) IP address of the router that SHOULD be used as
hop to the destinations listed in the Network Layer Reacha- the next hop to the destinations listed in the Network Layer
bility Information field of the UPDATE message. Reachability Information field of the UPDATE message.
Usage of this attribute is defined in 5.1.3. Usage of this attribute is defined in 5.1.3.
d) MULTI_EXIT_DISC (Type Code 4): d) MULTI_EXIT_DISC (Type Code 4):
This is an optional non-transitive attribute that is a four This is an optional non-transitive attribute that is a four
octet non-negative integer. The value of this attribute may octet unsigned integer. The value of this attribute MAY be
be used by a BGP speaker's decision process to discriminate used by a BGP speaker's decision process to discriminate
among multiple entry points to a neighboring autonomous sys- among multiple entry points to a neighboring autonomous
tem. system.
Usage of this attribute is defined in 5.1.4. Usage of this attribute is defined in 5.1.4.
e) LOCAL_PREF (Type Code 5): e) LOCAL_PREF (Type Code 5):
LOCAL_PREF is a well-known attribute that is a four octet LOCAL_PREF is a well-known attribute that is a four octet
non-negative integer. A BGP speaker uses it to inform other unsigned integer. A BGP speaker uses it to inform other
internal peers of the advertising speaker's degree of pref- internal peers of the advertising speaker's degree of pref-
erence for an advertised route. erence for an advertised route.
Usage of this attribute is defined in 5.1.5. Usage of this attribute is defined in 5.1.5.
f) ATOMIC_AGGREGATE (Type Code 6) f) ATOMIC_AGGREGATE (Type Code 6)
ATOMIC_AGGREGATE is a well-known discretionary attribute of ATOMIC_AGGREGATE is a well-known discretionary attribute of
length 0. length 0.
Usage of this attribute is defined in 5.1.6. Usage of this attribute is defined in 5.1.6.
g) AGGREGATOR (Type Code 7) g) AGGREGATOR (Type Code 7)
AGGREGATOR is an optional transitive attribute of length 6. AGGREGATOR is an optional transitive attribute of length 6.
The attribute contains the last AS number that formed the The attribute contains the last AS number that formed the
aggregate route (encoded as 2 octets), followed by the IP aggregate route (encoded as 2 octets), followed by the IP
address of the BGP speaker that formed the aggregate route address of the BGP speaker that formed the aggregate route
(encoded as 4 octets). This should be the same address as (encoded as 4 octets). This SHOULD be the same address as
the one used for the BGP Identifier of the speaker. the one used for the BGP Identifier of the speaker.
Usage of this attribute is defined in 5.1.7. Usage of this attribute is defined in 5.1.7.
Network Layer Reachability Information: Network Layer Reachability Information:
This variable length field contains a list of IP address pre- This variable length field contains a list of IP address pre-
fixes. The length in octets of the Network Layer Reachability fixes. The length in octets of the Network Layer Reachability
Information is not encoded explicitly, but can be calculated Information is not encoded explicitly, but can be calculated
as: as:
skipping to change at page 21, line 7 skipping to change at page 21, line 5
an IP prefix), which unambiguously identifies the route in the con- an IP prefix), which unambiguously identifies the route in the con-
text of the BGP speaker - BGP speaker connection to which it has been text of the BGP speaker - BGP speaker connection to which it has been
previously advertised. previously advertised.
An UPDATE message might advertise only routes to be withdrawn from An UPDATE message might advertise only routes to be withdrawn from
service, in which case it will not include path attributes or Network service, in which case it will not include path attributes or Network
Layer Reachability Information. Conversely, it may advertise only a Layer Reachability Information. Conversely, it may advertise only a
feasible route, in which case the WITHDRAWN ROUTES field need not be feasible route, in which case the WITHDRAWN ROUTES field need not be
present. present.
An UPDATE message should not include the same address prefix in the An UPDATE message SHOULD NOT include the same address prefix in the
WITHDRAWN ROUTES and Network Layer Reachability Information fields, WITHDRAWN ROUTES and Network Layer Reachability Information fields,
however a BGP speaker MUST be able to process UPDATE messages in this however a BGP speaker MUST be able to process UPDATE messages in this
form. A BGP speaker should treat an UPDATE message of this form as if form. A BGP speaker SHOULD treat an UPDATE message of this form as if
the WITHDRAWN ROUTES doesn't contain the address prefix. the WITHDRAWN ROUTES doesn't contain the address prefix.
4.4 KEEPALIVE Message Format 4.4 KEEPALIVE Message Format
BGP does not use any TCP-based keep-alive mechanism to determine if BGP does not use any TCP-based keep-alive mechanism to determine if
peers are reachable. Instead, KEEPALIVE messages are exchanged peers are reachable. Instead, KEEPALIVE messages are exchanged
between peers often enough as not to cause the Hold Timer to expire. between peers often enough as not to cause the Hold Timer to expire.
A reasonable maximum time between KEEPALIVE messages would be one A reasonable maximum time between KEEPALIVE messages would be one
third of the Hold Time interval. KEEPALIVE messages MUST NOT be sent third of the Hold Time interval. KEEPALIVE messages MUST NOT be sent
more frequently than one per second. An implementation MAY adjust the more frequently than one per second. An implementation MAY adjust the
rate at which it sends KEEPALIVE messages as a function of the Hold rate at which it sends KEEPALIVE messages as a function of the Hold
Time interval. Time interval.
If the negotiated Hold Time interval is zero, then periodic KEEPALIVE If the negotiated Hold Time interval is zero, then periodic KEEPALIVE
messages MUST NOT be sent. messages MUST NOT be sent.
KEEPALIVE message consists of only message header and has a length of A KEEPALIVE message consists of only message header and has a length
19 octets. of 19 octets.
4.5 NOTIFICATION Message Format 4.5 NOTIFICATION Message Format
A NOTIFICATION message is sent when an error condition is detected. A NOTIFICATION message is sent when an error condition is detected.
The BGP connection is closed immediately after sending it. The BGP connection is closed immediately after sending it.
In addition to the fixed-size BGP header, the NOTIFICATION message In addition to the fixed-size BGP header, the NOTIFICATION message
contains the following fields: contains the following fields:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error code | Error subcode | Data (variable) | | Error code | Error subcode | Data (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Error Code: Error Code:
This 1-octet unsigned integer indicates the type of This 1-octet unsigned integer indicates the type of NOTIFICA-
NOTIFICATION. The following Error Codes have been defined: TION. The following Error Codes have been defined:
Error Code Symbolic Name Reference Error Code Symbolic Name Reference
1 Message Header Error Section 6.1 1 Message Header Error Section 6.1
2 OPEN Message Error Section 6.2 2 OPEN Message Error Section 6.2
3 UPDATE Message Error Section 6.3 3 UPDATE Message Error Section 6.3
4 Hold Timer Expired Section 6.5 4 Hold Timer Expired Section 6.5
5 Finite State Machine Error Section 6.6 5 Finite State Machine Error Section 6.6
skipping to change at page 22, line 40 skipping to change at page 22, line 36
1 - Connection Not Synchronized. 1 - Connection Not Synchronized.
2 - Bad Message Length. 2 - Bad Message Length.
3 - Bad Message Type. 3 - Bad Message Type.
OPEN Message Error subcodes: OPEN Message Error subcodes:
1 - Unsupported Version Number. 1 - Unsupported Version Number.
2 - Bad Peer AS. 2 - Bad Peer AS.
3 - Bad BGP Identifier. 3 - Bad BGP Identifier.
4 - Unsupported Optional Parameter. 4 - Unsupported Optional Parameter.
5 - Authentication Failure. 5 - [Deprecated - see Appendix A].
6 - Unacceptable Hold Time. 6 - Unacceptable Hold Time.
UPDATE Message Error subcodes: UPDATE Message Error subcodes:
1 - Malformed Attribute List. 1 - Malformed Attribute List.
2 - Unrecognized Well-known Attribute. 2 - Unrecognized Well-known Attribute.
3 - Missing Well-known Attribute. 3 - Missing Well-known Attribute.
4 - Attribute Flags Error. 4 - Attribute Flags Error.
5 - Attribute Length Error. 5 - Attribute Length Error.
6 - Invalid ORIGIN Attribute 6 - Invalid ORIGIN Attribute.
7 - [Deprecated - see Appendix A].
8 - Invalid NEXT_HOP Attribute. 8 - Invalid NEXT_HOP Attribute.
9 - Optional Attribute Error. 9 - Optional Attribute Error.
10 - Invalid Network Field. 10 - Invalid Network Field.
11 - Malformed AS_PATH. 11 - Malformed AS_PATH.
Data: Data:
This variable-length field is used to diagnose the reason for This variable-length field is used to diagnose the reason for
the NOTIFICATION. The contents of the Data field depend upon the NOTIFICATION. The contents of the Data field depend upon
the Error Code and Error Subcode. See Section 6 below for more the Error Code and Error Subcode. See Section 6 below for more
details. details.
Note that the length of the Data field can be determined from Note that the length of the Data field can be determined from
skipping to change at page 23, line 35 skipping to change at page 23, line 33
This section discusses the path attributes of the UPDATE message. This section discusses the path attributes of the UPDATE message.
Path attributes fall into four separate categories: Path attributes fall into four separate categories:
1. Well-known mandatory. 1. Well-known mandatory.
2. Well-known discretionary. 2. Well-known discretionary.
3. Optional transitive. 3. Optional transitive.
4. Optional non-transitive. 4. Optional non-transitive.
Well-known attributes must be recognized by all BGP implementations. Well-known attributes MUST be recognized by all BGP implementations.
Some of these attributes are mandatory and must be included in every Some of these attributes are mandatory and MUST be included in every
UPDATE message that contains NLRI. Others are discretionary and may UPDATE message that contains NLRI. Others are discretionary and MAY
or may not be sent in a particular UPDATE message. or MAY NOT be sent in a particular UPDATE message.
All well-known attributes must be passed along (after proper updat- All well-known attributes MUST be passed along (after proper updat-
ing, if necessary) to other BGP peers. ing, if necessary) to other BGP peers.
In addition to well-known attributes, each path may contain one or In addition to well-known attributes, each path MAY contain one or
more optional attributes. It is not required or expected that all BGP more optional attributes. It is not required or expected that all BGP
implementations support all optional attributes. The handling of an implementations support all optional attributes. The handling of an
unrecognized optional attribute is determined by the setting of the unrecognized optional attribute is determined by the setting of the
Transitive bit in the attribute flags octet. Paths with unrecognized Transitive bit in the attribute flags octet. Paths with unrecognized
transitive optional attributes should be accepted. If a path with transitive optional attributes SHOULD be accepted. If a path with
unrecognized transitive optional attribute is accepted and passed unrecognized transitive optional attribute is accepted and passed
along to other BGP peers, then the unrecognized transitive optional along to other BGP peers, then the unrecognized transitive optional
attribute of that path must be passed along with the path to other attribute of that path MUST be passed along with the path to other
BGP peers with the Partial bit in the Attribute Flags octet set to 1. BGP peers with the Partial bit in the Attribute Flags octet set to 1.
If a path with recognized transitive optional attribute is accepted If a path with recognized transitive optional attribute is accepted
and passed along to other BGP peers and the Partial bit in the and passed along to other BGP peers and the Partial bit in the
Attribute Flags octet is set to 1 by some previous AS, it is not set Attribute Flags octet is set to 1 by some previous AS, it is not set
back to 0 by the current AS. Unrecognized non-transitive optional back to 0 by the current AS. Unrecognized non-transitive optional
attributes must be quietly ignored and not passed along to other BGP attributes MUST be quietly ignored and not passed along to other BGP
peers. peers.
New transitive optional attributes may be attached to the path by the New transitive optional attributes MAY be attached to the path by the
originator or by any other BGP speaker in the path. If they are not originator or by any other BGP speaker in the path. If they are not
attached by the originator, the Partial bit in the Attribute Flags attached by the originator, the Partial bit in the Attribute Flags
octet is set to 1. The rules for attaching new non-transitive octet is set to 1. The rules for attaching new non-transitive
optional attributes will depend on the nature of the specific optional attributes will depend on the nature of the specific
attribute. The documentation of each new non-transitive optional attribute. The documentation of each new non-transitive optional
attribute will be expected to include such rules. (The description of attribute will be expected to include such rules. (The description of
the MULTI_EXIT_DISC attribute gives an example.) All optional the MULTI_EXIT_DISC attribute gives an example.) All optional
attributes (both transitive and non-transitive) may be updated (if attributes (both transitive and non-transitive) MAY be updated (if
appropriate) by BGP speakers in the path. appropriate) by BGP speakers in the path.
The sender of an UPDATE message should order path attributes within The sender of an UPDATE message SHOULD order path attributes within
the UPDATE message in ascending order of attribute type. The receiver the UPDATE message in ascending order of attribute type. The receiver
of an UPDATE message must be prepared to handle path attributes of an UPDATE message MUST be prepared to handle path attributes
within the UPDATE message that are out of order. within the UPDATE message that are out of order.
The same attribute can not appear more than once within the Path The same attribute (attribute with the same type) can not appear more
Attributes field of a particular UPDATE message. than once within the Path Attributes field of a particular UPDATE
message.
The mandatory category refers to an attribute which must be present The mandatory category refers to an attribute which MUST be present
in both IBGP and EBGP exchanges if NLRI are contained in the UPDATE in both IBGP and EBGP exchanges if NLRI are contained in the UPDATE
message. Attributes classified as optional for the purpose of the message. Attributes classified as optional for the purpose of the
protocol extension mechanism may be purely discretionary, or discre- protocol extension mechanism may be purely discretionary, or discre-
tionary, required, or disallowed in certain contexts. tionary, required, or disallowed in certain contexts.
attribute EBGP IBGP attribute EBGP IBGP
ORIGIN mandatory mandatory ORIGIN mandatory mandatory
AS_PATH mandatory mandatory AS_PATH mandatory mandatory
NEXT_HOP mandatory mandatory NEXT_HOP mandatory mandatory
MULTI_EXIT_DISC discretionary discretionary MULTI_EXIT_DISC discretionary discretionary
LOCAL_PREF see section 5.1.5 required LOCAL_PREF see Section 5.1.5 required
ATOMIC_AGGREGATE see section 5.1.6 and 9.1.4 ATOMIC_AGGREGATE see Section 5.1.6 and 9.1.4
AGGREGATOR discretionary discretionary AGGREGATOR discretionary discretionary
5.1 Path Attribute Usage 5.1 Path Attribute Usage
The usage of each BGP path attributes is described in the following The usage of each BGP path attribute is described in the following
clauses. clauses.
5.1.1 ORIGIN 5.1.1 ORIGIN
ORIGIN is a well-known mandatory attribute. The ORIGIN attribute ORIGIN is a well-known mandatory attribute. The ORIGIN attribute is
shall be generated by the speaker that originates the associated generated by the speaker that originates the associated routing
routing information. Its value SHOULD NOT be changed by any other information. Its value SHOULD NOT be changed by any other speaker.
speaker.
5.1.2 AS_PATH 5.1.2 AS_PATH
AS_PATH is a well-known mandatory attribute. This attribute identi- AS_PATH is a well-known mandatory attribute. This attribute identi-
fies the autonomous systems through which routing information carried fies the autonomous systems through which routing information carried
in this UPDATE message has passed. The components of this list can be in this UPDATE message has passed. The components of this list can be
AS_SETs or AS_SEQUENCEs. AS_SETs or AS_SEQUENCEs.
When a BGP speaker propagates a route which it has learned from When a BGP speaker propagates a route which it has learned from
another BGP speaker's UPDATE message, it shall modify the route's another BGP speaker's UPDATE message, it modifies the route's AS_PATH
AS_PATH attribute based on the location of the BGP speaker to which attribute based on the location of the BGP speaker to which the route
the route will be sent: will be sent:
a) When a given BGP speaker advertises the route to an internal a) When a given BGP speaker advertises the route to an internal
peer, the advertising speaker shall not modify the AS_PATH peer, the advertising speaker SHALL NOT modify the AS_PATH
attribute associated with the route. attribute associated with the route.
b) When a given BGP speaker advertises the route to an external b) When a given BGP speaker advertises the route to an external
peer, then the advertising speaker shall update the AS_PATH peer, then the advertising speaker updates the AS_PATH attribute
attribute as follows: as follows:
1) if the first path segment of the AS_PATH is of type 1) if the first path segment of the AS_PATH is of type
AS_SEQUENCE, the local system shall prepend its own AS number AS_SEQUENCE, the local system prepends its own AS number as the
as the last element of the sequence (put it in the leftmost last element of the sequence (put it in the leftmost position).
position). If the act of prepending will cause an overflow in If the act of prepending will cause an overflow in the AS_PATH
the AS_PATH segment, i.e. more than 255 ASs, it shall be legal segment, i.e. more than 255 ASs, it is legal to prepend a new
to prepend a new segment of type AS_SEQUENCE and prepend its segment of type AS_SEQUENCE and prepend its own AS number to
own AS number to this new segment. this new segment.
2) if the first path segment of the AS_PATH is of type AS_SET, 2) if the first path segment of the AS_PATH is of type AS_SET,
the local system shall prepend a new path segment of type the local system prepends a new path segment of type
AS_SEQUENCE to the AS_PATH, including its own AS number in that AS_SEQUENCE to the AS_PATH, including its own AS number in that
segment. segment.
When a BGP speaker originates a route then: When a BGP speaker originates a route then:
a) the originating speaker shall include its own AS number in a a) the originating speaker includes its own AS number in a path
path segment of type AS_SEQUENCE in the AS_PATH attribute of all segment of type AS_SEQUENCE in the AS_PATH attribute of all UPDATE
UPDATE messages sent to an external peer. (In this case, the AS messages sent to an external peer. (In this case, the AS number of
number of the originating speaker's autonomous system will be the the originating speaker's autonomous system will be the only entry
only entry the path segment, and this path segment will be the the path segment, and this path segment will be the only segment
only segment in the AS_PATH attribute). in the AS_PATH attribute).
b) the originating speaker shall include an empty AS_PATH b) the originating speaker includes an empty AS_PATH attribute in
attribute in all UPDATE messages sent to internal peers. (An all UPDATE messages sent to internal peers. (An empty AS_PATH
empty AS_PATH attribute is one whose length field contains the attribute is one whose length field contains the value zero).
value zero).
Whenever the modification of the AS_PATH attribute calls for includ- Whenever the modification of the AS_PATH attribute calls for includ-
ing or prepending the AS number of the local system, the local system ing or prepending the AS number of the local system, the local system
may include/prepend more than one instance of its own AS number in MAY include/prepend more than one instance of its own AS number in
the AS_PATH attribute. This is controlled via local configuration. the AS_PATH attribute. This is controlled via local configuration.
5.1.3 NEXT_HOP 5.1.3 NEXT_HOP
The NEXT_HOP is a well-known mandatory attribute that defines the IP The NEXT_HOP is a well-known mandatory attribute that defines the IP
address of the border router that should be used as the next hop to address of the router that SHOULD be used as the next hop to the des-
the destinations listed in the UPDATE message. The NEXT_HOP attribute tinations listed in the UPDATE message. The NEXT_HOP attribute is
is calculated as follows. calculated as follows.
1) When sending a message to an internal peer, if the route is not 1) When sending a message to an internal peer, if the route is not
locally originated the BGP speaker should not modify the NEXT_HOP locally originated the BGP speaker SHOULD NOT modify the NEXT_HOP
attribute, unless it has been explicitly configured to announce attribute, unless it has been explicitly configured to announce
its own IP address as the NEXT_HOP. When announcing a locally its own IP address as the NEXT_HOP. When announcing a locally
originated route to an internal peer, the BGP speaker should use originated route to an internal peer, the BGP speaker SHOULD use
as the NEXT_HOP the interface address of the router through which as the NEXT_HOP the interface address of the router through which
the announced network is reachable for the speaker; if the route the announced network is reachable for the speaker; if the route
is directly connected to the speaker, or the interface address of is directly connected to the speaker, or the interface address of
the router through which the announced network is reachable for the router through which the announced network is reachable for
the speaker is the internal peer's address, then the BGP speaker the speaker is the internal peer's address, then the BGP speaker
should use for the NEXT_HOP attribute its own IP address (the SHOULD use for the NEXT_HOP attribute its own IP address (the
address of the interface that is used to reach the peer). address of the interface that is used to reach the peer).
2) When sending a message to an external peer X, and the peer is 2) When sending a message to an external peer X, and the peer is
one IP hop away from the speaker: one IP hop away from the speaker:
- If the route being announced was learned from an internal - If the route being announced was learned from an internal
peer or is locally originated, the BGP speaker can use for the peer or is locally originated, the BGP speaker can use for the
NEXT_HOP attribute an interface address of the internal peer NEXT_HOP attribute an interface address of the internal peer
router (or the internal router) through which the announced router (or the internal router) through which the announced
network is reachable for the speaker, provided that peer X network is reachable for the speaker, provided that peer X
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- Otherwise, if the route being announced was learned from an - Otherwise, if the route being announced was learned from an
external peer, the speaker can use in the NEXT_HOP attribute an external peer, the speaker can use in the NEXT_HOP attribute an
IP address of any adjacent router (known from the received IP address of any adjacent router (known from the received
NEXT_HOP attribute) that the speaker itself uses for local NEXT_HOP attribute) that the speaker itself uses for local
route calculation, provided that peer X shares a common subnet route calculation, provided that peer X shares a common subnet
with this address. This is a second form of "third party" with this address. This is a second form of "third party"
NEXT_HOP attribute. NEXT_HOP attribute.
- Otherwise, if the external peer to which the route is being - Otherwise, if the external peer to which the route is being
advertised shares a common subnet with one of the announcing advertised shares a common subnet with one of the interfaces of
router's own interfaces, the router may use the IP address the announcing BGP speaker, the speaker MAY use the IP address
associated with such an interface in the NEXT_HOP attribute. associated with such an interface in the NEXT_HOP attribute.
This is known as a "first party" NEXT_HOP attribute. This is known as a "first party" NEXT_HOP attribute.
- By default (if none of the above conditions apply), the BGP - By default (if none of the above conditions apply), the BGP
speaker should use in the NEXT_HOP attribute the IP address of speaker SHOULD use in the NEXT_HOP attribute the IP address of
the interface that the speaker uses to establish the BGP con- the interface that the speaker uses to establish the BGP con-
nection to peer X. nection to peer X.
3) When sending a message to an external peer X, and the peer is 3) When sending a message to an external peer X, and the peer is
multiple IP hops away from the speaker (aka "multihop EBGP"): multiple IP hops away from the speaker (aka "multihop EBGP"):
- The speaker may be configured to propagate the NEXT_HOP - The speaker MAY be configured to propagate the NEXT_HOP
attribute. In this case when advertising a route that the attribute. In this case when advertising a route that the
speaker learned from one of its peers, the NEXT_HOP attribute speaker learned from one of its peers, the NEXT_HOP attribute
of the advertised route is exactly the same as the NEXT_HOP of the advertised route is exactly the same as the NEXT_HOP
attribute of the learned route (the speaker just doesn't modify attribute of the learned route (the speaker just doesn't modify
the NEXT_HOP attribute). the NEXT_HOP attribute).
- By default, the BGP speaker should use in the NEXT_HOP - By default, the BGP speaker SHOULD use in the NEXT_HOP
attribute the IP address of the interface that the speaker uses attribute the IP address of the interface that the speaker uses
to establish the BGP connection to peer X. to establish the BGP connection to peer X.
Normally the NEXT_HOP attribute is chosen such that the shortest Normally the NEXT_HOP attribute is chosen such that the shortest
available path will be taken. A BGP speaker must be able to support available path will be taken. A BGP speaker MUST be able to support
disabling advertisement of third party NEXT_HOP attributes to handle disabling advertisement of third party NEXT_HOP attributes to handle
imperfectly bridged media. imperfectly bridged media.
A BGP speaker must never advertise an address of a peer to that peer A route originated by a BGP speaker SHALL NOT be advertised to a peer
as a NEXT_HOP, for a route that the speaker is originating. A BGP using an address of that peer as NEXT_HOP. A BGP speaker SHALL NOT
speaker must never install a route with itself as the next hop. install a route with itself as the next hop.
The NEXT_HOP attribute is used by the BGP speaker to determine the The NEXT_HOP attribute is used by the BGP speaker to determine the
actual outbound interface and immediate next-hop address that should actual outbound interface and immediate next-hop address that SHOULD
be used to forward transit packets to the associated destinations. be used to forward transit packets to the associated destinations.
The immediate next-hop address is determined by performing a recur- The immediate next-hop address is determined by performing a recur-
sive route lookup operation for the IP address in the NEXT_HOP sive route lookup operation for the IP address in the NEXT_HOP
attribute using the contents of the Routing Table, selecting one attribute using the contents of the Routing Table, selecting one
entry if multiple entries of equal cost exist. The Routing Table entry if multiple entries of equal cost exist. The Routing Table
entry which resolves the IP address in the NEXT_HOP attribute will entry which resolves the IP address in the NEXT_HOP attribute will
always specify the outbound interface. If the entry specifies an always specify the outbound interface. If the entry specifies an
attached subnet, but does not specify a next-hop address, then the attached subnet, but does not specify a next-hop address, then the
address in the NEXT_HOP attribute should be used as the immediate address in the NEXT_HOP attribute SHOULD be used as the immediate
next-hop address. If the entry also specifies the next-hop address, next-hop address. If the entry also specifies the next-hop address,
this address should be used as the immediate next-hop address for this address SHOULD be used as the immediate next-hop address for
packet forwarding. packet forwarding.
5.1.4 MULTI_EXIT_DISC 5.1.4 MULTI_EXIT_DISC
The MULTI_EXIT_DISC is an optional non-transitive attribute which may The MULTI_EXIT_DISC is an optional non-transitive attribute which is
be used on external (inter-AS) links to discriminate among multiple intended to be used on external (inter-AS) links to discriminate
exit or entry points to the same neighboring AS. The value of the among multiple exit or entry points to the same neighboring AS. The
MULTI_EXIT_DISC attribute is a four octet unsigned number which is value of the MULTI_EXIT_DISC attribute is a four octet unsigned num-
called a metric. All other factors being equal, the exit point with ber which is called a metric. All other factors being equal, the exit
lower metric should be preferred. If received over EBGP, the point with lower metric SHOULD be preferred. If received over EBGP,
MULTI_EXIT_DISC attribute MAY be propagated over IBGP to other BGP the MULTI_EXIT_DISC attribute MAY be propagated over IBGP to other
speakers within the same AS. The MULTI_EXIT_DISC attribute received BGP speakers within the same AS. The MULTI_EXIT_DISC attribute
from a neighboring AS MUST NOT be propagated to other neighboring received from a neighboring AS MUST NOT be propagated to other neigh-
ASs. boring ASs.
A BGP speaker MUST IMPLEMENT a mechanism based on local configuration A BGP speaker MUST IMPLEMENT a mechanism based on local configuration
which allows the MULTI_EXIT_DISC attribute to be removed from a which allows the MULTI_EXIT_DISC attribute to be removed from a
route. This MAY be done prior to determining the degree of preference route. This MAY be done prior to determining the degree of preference
of the route and performing route selection (decision process phases of the route and performing route selection (decision process phases
1 and 2). 1 and 2).
An implementation MAY also (based on local configuration) alter the An implementation MAY also (based on local configuration) alter the
value of the MULTI_EXIT_DISC attribute received over EBGP. This MAY value of the MULTI_EXIT_DISC attribute received over EBGP. This MAY
be done prior to determining the degree of preference of the route be done prior to determining the degree of preference of the route
and performing route selection (decision process phases 1 and 2). See and performing route selection (decision process phases 1 and 2). See
section 9.1.2.2 for necessary restricts on this. Section 9.1.2.2 for necessary restrictions on this.
5.1.5 LOCAL_PREF 5.1.5 LOCAL_PREF
LOCAL_PREF is a well-known attribute that SHALL be included in all LOCAL_PREF is a well-known attribute that SHALL be included in all
UPDATE messages that a given BGP speaker sends to the other internal UPDATE messages that a given BGP speaker sends to the other internal
peers. A BGP speaker SHALL calculate the degree of preference for peers. A BGP speaker SHALL calculate the degree of preference for
each external route based on the locally configured policy, and each external route based on the locally configured policy, and
include the degree of preference when advertising a route to its include the degree of preference when advertising a route to its
internal peers. The higher degree of preference MUST be preferred. A internal peers. The higher degree of preference MUST be preferred. A
BGP speaker shall use the degree of preference learned via LOCAL_PREF BGP speaker uses the degree of preference learned via LOCAL_PREF in
in its decision process (see section 9.1.1). its decision process (see Section 9.1.1).
A BGP speaker MUST NOT include this attribute in UPDATE messages that A BGP speaker MUST NOT include this attribute in UPDATE messages that
it sends to external peers, except for the case of BGP Confederations it sends to external peers, except for the case of BGP Confederations
[RFC3065]. If it is contained in an UPDATE message that is received [RFC3065]. If it is contained in an UPDATE message that is received
from an external peer, then this attribute MUST be ignored by the from an external peer, then this attribute MUST be ignored by the
receiving speaker, except for the case of BGP Confederations receiving speaker, except for the case of BGP Confederations
[RF3065]. [RF3065].
5.1.6 ATOMIC_AGGREGATE 5.1.6 ATOMIC_AGGREGATE
ATOMIC_AGGREGATE is a well-known discretionary attribute. ATOMIC_AGGREGATE is a well-known discretionary attribute.
When a router aggregates several routes for the purpose of advertise- When a BGP speaker aggregates several routes for the purpose of
ment to a particular peer, the AS_PATH of the aggregated route nor- advertisement to a particular peer, the AS_PATH of the aggregated
mally includes an AS_SET formed from the set of AS from which the route normally includes an AS_SET formed from the set of ASs from
aggregate was formed. In many cases the network administrator can which the aggregate was formed. In many cases the network adminis-
determine that the aggregate can safely be advertised without the trator can determine that the aggregate can safely be advertised
AS_SET and not form route loops. without the AS_SET and not form route loops.
If an aggregate excludes at least some of the AS numbers present in If an aggregate excludes at least some of the AS numbers present in
the AS_PATH of the routes that are aggregated as a result of dropping the AS_PATH of the routes that are aggregated as a result of dropping
the AS_SET, the aggregated route, when advertised to the peer, SHOULD the AS_SET, the aggregated route, when advertised to the peer, SHOULD
include the ATOMIC_AGGREGATE attribute. include the ATOMIC_AGGREGATE attribute.
A BGP speaker that receives a route with the ATOMIC_AGGREGATE A BGP speaker that receives a route with the ATOMIC_AGGREGATE
attribute SHOULD NOT remove the attribute from the route when propa- attribute SHOULD NOT remove the attribute from the route when propa-
gating it to other speakers. gating it to other speakers.
skipping to change at page 30, line 7 skipping to change at page 30, line 7
defined in 9.1.4) when advertising this route to other BGP speakers. defined in 9.1.4) when advertising this route to other BGP speakers.
A BGP speaker that receives a route with the ATOMIC_AGGREGATE A BGP speaker that receives a route with the ATOMIC_AGGREGATE
attribute needs to be cognizant of the fact that the actual path to attribute needs to be cognizant of the fact that the actual path to
destinations, as specified in the NLRI of the route, while having the destinations, as specified in the NLRI of the route, while having the
loop-free property, may not be the path specified in the AS_PATH loop-free property, may not be the path specified in the AS_PATH
attribute of the route. attribute of the route.
5.1.7 AGGREGATOR 5.1.7 AGGREGATOR
AGGREGATOR is an optional transitive attribute which may be included AGGREGATOR is an optional transitive attribute which MAY be included
in updates which are formed by aggregation (see Section 9.2.2.2). A in updates which are formed by aggregation (see Section 9.2.2.2). A
BGP speaker which performs route aggregation may add the AGGREGATOR BGP speaker which performs route aggregation MAY add the AGGREGATOR
attribute which shall contain its own AS number and IP address. The attribute which SHALL contain its own AS number and IP address. The
IP address should be the same as the BGP Identifier of the speaker. IP address SHOULD be the same as the BGP Identifier of the speaker.
6. BGP Error Handling. 6. BGP Error Handling.
This section describes actions to be taken when errors are detected This section describes actions to be taken when errors are detected
while processing BGP messages. while processing BGP messages.
When any of the conditions described here are detected, a NOTIFICA- When any of the conditions described here are detected, a NOTIFICA-
TION message with the indicated Error Code, Error Subcode, and Data TION message with the indicated Error Code, Error Subcode, and Data
fields is sent, and the BGP connection is closed, unless it is fields is sent, and the BGP connection is closed, unless it is
explicitly stated that no NOTIFICATION message is to be sent and the explicitly stated that no NOTIFICATION message is to be sent and the
BGP connection is not to be closed. If no Error Subcode is specified, BGP connection is not to be closed. If no Error Subcode is specified,
then a zero must be used. then a zero MUST be used.
The phrase "the BGP connection is closed" means that the TCP connec- The phrase "the BGP connection is closed" means that the TCP connec-
tion has been closed, the associated Adj-RIB-In has been cleared, and tion has been closed, the associated Adj-RIB-In has been cleared, and
that all resources for that BGP connection have been deallocated. that all resources for that BGP connection have been deallocated.
Entries in the Loc-RIB associated with the remote peer are marked as Entries in the Loc-RIB associated with the remote peer are marked as
invalid. The fact that the routes have become invalid is passed to invalid. The fact that the routes have become invalid is passed to
other BGP peers before the routes are deleted from the system. other BGP peers before the routes are deleted from the system.
Unless specified explicitly, the Data field of the NOTIFICATION mes- Unless specified explicitly, the Data field of the NOTIFICATION mes-
sage that is sent to indicate an error is empty. sage that is sent to indicate an error is empty.
skipping to change at page 33, line 7 skipping to change at page 33, line 7
If the ORIGIN attribute has an undefined value, then the Error Sub- If the ORIGIN attribute has an undefined value, then the Error Sub-
code is set to Invalid Origin Attribute. The Data field contains the code is set to Invalid Origin Attribute. The Data field contains the
unrecognized attribute (type, length and value). unrecognized attribute (type, length and value).
If the NEXT_HOP attribute field is syntactically incorrect, then the If the NEXT_HOP attribute field is syntactically incorrect, then the
Error Subcode is set to Invalid NEXT_HOP Attribute. The Data field Error Subcode is set to Invalid NEXT_HOP Attribute. The Data field
contains the incorrect attribute (type, length and value). Syntactic contains the incorrect attribute (type, length and value). Syntactic
correctness means that the NEXT_HOP attribute represents a valid IP correctness means that the NEXT_HOP attribute represents a valid IP
host address. host address.
The IP address in the NEXT_HOP must meet the following criteria to be The IP address in the NEXT_HOP MUST meet the following criteria to be
considered semantically correct: considered semantically correct:
a) It must not be the IP address of the receiving speaker a) It MUST NOT be the IP address of the receiving speaker
b) In the case of an EBGP where the sender and receiver are one IP b) In the case of an EBGP where the sender and receiver are one IP
hop away from each other, either the IP address in the NEXT_HOP hop away from each other, either the IP address in the NEXT_HOP
must be the sender's IP address (that is used to establish the BGP MUST be the sender's IP address (that is used to establish the BGP
connection), or the interface associated with the NEXT_HOP IP connection), or the interface associated with the NEXT_HOP IP
address must share a common subnet with the receiving BGP speaker. address MUST share a common subnet with the receiving BGP speaker.
If the NEXT_HOP attribute is semantically incorrect, the error should If the NEXT_HOP attribute is semantically incorrect, the error SHOULD
be logged, and the route should be ignored. In this case, no NOTIFI- be logged, and the route SHOULD be ignored. In this case, a NOTIFICA-
CATION message should be sent, and connection should not be closed. TION message SHOULD NOT be sent, and connection SHOULD NOT be closed.
The AS_PATH attribute is checked for syntactic correctness. If the The AS_PATH attribute is checked for syntactic correctness. If the
path is syntactically incorrect, then the Error Subcode is set to path is syntactically incorrect, then the Error Subcode is set to
Malformed AS_PATH. Malformed AS_PATH.
If the UPDATE message is received from an external peer, the local If the UPDATE message is received from an external peer, the local
system MAY check whether the leftmost AS in the AS_PATH attribute is system MAY check whether the leftmost AS in the AS_PATH attribute is
equal to the autonomous system number of the peer than sent the mes- equal to the autonomous system number of the peer that sent the mes-
sage. If the check determines that this is not the case, the Error sage. If the check determines that this is not the case, the Error
Subcode is set to Malformed AS_PATH. Subcode is set to Malformed AS_PATH.
If an optional attribute is recognized, then the value of this If an optional attribute is recognized, then the value of this
attribute is checked. If an error is detected, the attribute is dis- attribute is checked. If an error is detected, the attribute is dis-
carded, and the Error Subcode is set to Optional Attribute Error. carded, and the Error Subcode is set to Optional Attribute Error.
The Data field contains the attribute (type, length and value). The Data field contains the attribute (type, length and value).
If any attribute appears more than once in the UPDATE message, then If any attribute appears more than once in the UPDATE message, then
the Error Subcode is set to Malformed Attribute List. the Error Subcode is set to Malformed Attribute List.
The NLRI field in the UPDATE message is checked for syntactic valid- The NLRI field in the UPDATE message is checked for syntactic valid-
ity. If the field is syntactically incorrect, then the Error Subcode ity. If the field is syntactically incorrect, then the Error Subcode
is set to Invalid Network Field. is set to Invalid Network Field.
If a prefix in the NLRI field is semantically incorrect (e.g., an If a prefix in the NLRI field is semantically incorrect (e.g., an
unexpected multicast IP address), an error should be logged locally, unexpected multicast IP address), an error SHOULD be logged locally,
and the prefix should be ignored. and the prefix SHOULD be ignored.
An UPDATE message that contains correct path attributes, but no NLRI, An UPDATE message that contains correct path attributes, but no NLRI,
shall be treated as a valid UPDATE message. SHALL be treated as a valid UPDATE message.
6.4 NOTIFICATION message error handling. 6.4 NOTIFICATION message error handling.
If a peer sends a NOTIFICATION message, and the receiver of the mes- If a peer sends a NOTIFICATION message, and the receiver of the mes-
sage detects an error in that message, the receiver can not use a sage detects an error in that message, the receiver can not use a
NOTIFICATION message to report this error back to the peer. Any such NOTIFICATION message to report this error back to the peer. Any such
error, such as an unrecognized Error Code or Error Subcode, should be error, such as an unrecognized Error Code or Error Subcode, SHOULD be
noticed, logged locally, and brought to the attention of the adminis- noticed, logged locally, and brought to the attention of the adminis-
tration of the peer. The means to do this, however, lies outside the tration of the peer. The means to do this, however, lies outside the
scope of this document. scope of this document.
6.5 Hold Timer Expired error handling. 6.5 Hold Timer Expired error handling.
If a system does not receive successive KEEPALIVE and/or UPDATE If a system does not receive successive KEEPALIVE and/or UPDATE
and/or NOTIFICATION messages within the period specified in the Hold and/or NOTIFICATION messages within the period specified in the Hold
Time field of the OPEN message, then the NOTIFICATION message with Time field of the OPEN message, then the NOTIFICATION message with
Hold Timer Expired Error Code must be sent and the BGP connection Hold Timer Expired Error Code is sent and the BGP connection is
closed. closed.
6.6 Finite State Machine error handling. 6.6 Finite State Machine error handling.
Any error detected by the BGP Finite State Machine (e.g., receipt of Any error detected by the BGP Finite State Machine (e.g., receipt of
an unexpected event) is indicated by sending the NOTIFICATION message an unexpected event) is indicated by sending the NOTIFICATION message
with Error Code Finite State Machine Error. with Error Code Finite State Machine Error.
6.7 Cease. 6.7 Cease.
In absence of any fatal errors (that are indicated in this section), In absence of any fatal errors (that are indicated in this section),
a BGP peer may choose at any given time to close its BGP connection a BGP peer MAY choose at any given time to close its BGP connection
by sending the NOTIFICATION message with Error Code Cease. However, by sending the NOTIFICATION message with Error Code Cease. However,
the Cease NOTIFICATION message must not be used when a fatal error the Cease NOTIFICATION message MUST NOT be used when a fatal error
indicated by this section does exist. indicated by this section does exist.
A BGP speaker may support the ability to impose an (locally config- A BGP speaker MAY support the ability to impose an (locally config-
ured) upper bound on the number of address prefixes the speaker is ured) upper bound on the number of address prefixes the speaker is
willing to accept from a neighbor. When the upper bound is reached, willing to accept from a neighbor. When the upper bound is reached,
the speaker (under control of local configuration) may either (a) the speaker (under control of local configuration) either (a) dis-
discard new address prefixes from the neighbor (while maintaining BGP cards new address prefixes from the neighbor (while maintaining BGP
connection with the neighbor), or (b) terminate the BGP connection connection with the neighbor), or (b) terminates the BGP connection
with the neighbor. If the BGP speaker decides to terminate its BGP with the neighbor. If the BGP speaker decides to terminate its BGP
connection with a neighbor because the number of address prefixes connection with a neighbor because the number of address prefixes
received from the neighbor exceeds the locally configured upper received from the neighbor exceeds the locally configured upper
bound, then the speaker must send to the neighbor a NOTIFICATION mes- bound, then the speaker MUST send to the neighbor a NOTIFICATION mes-
sage with the Error Code Cease. sage with the Error Code Cease.
6.8 BGP connection collision detection. 6.8 BGP connection collision detection.
If a pair of BGP speakers try simultaneously to establish a BGP con- If a pair of BGP speakers try simultaneously to establish a BGP con-
nection to each other, then two parallel connections between this nection to each other, then two parallel connections between this
pair of speakers might well be formed. If the source IP address used pair of speakers might well be formed. If the source IP address used
by one of these connections is the same as the destination IP address by one of these connections is the same as the destination IP address
used by the other, and the destination IP address used by the first used by the other, and the destination IP address used by the first
connection is the same as the source IP address used by the other, we connection is the same as the source IP address used by the other, we
refer to this situation as connection collision. Clearly in the refer to this situation as connection collision. Clearly in the
presence of connection collision, one of these connections must be presence of connection collision, one of these connections MUST be
closed. closed.
Based on the value of the BGP Identifier a convention is established Based on the value of the BGP Identifier a convention is established
for detecting which BGP connection is to be preserved when a colli- for detecting which BGP connection is to be preserved when a colli-
sion does occur. The convention is to compare the BGP Identifiers of sion does occur. The convention is to compare the BGP Identifiers of
the peers involved in the collision and to retain only the connection the peers involved in the collision and to retain only the connection
initiated by the BGP speaker with the higher-valued BGP Identifier. initiated by the BGP speaker with the higher-valued BGP Identifier.
Upon receipt of an OPEN message, the local system must examine all of Upon receipt of an OPEN message, the local system MUST examine all of
its connections that are in the OpenConfirm state. A BGP speaker may its connections that are in the OpenConfirm state. A BGP speaker MAY
also examine connections in an OpenSent state if it knows the BGP also examine connections in an OpenSent state if it knows the BGP
Identifier of the peer by means outside of the protocol. If among Identifier of the peer by means outside of the protocol. If among
these connections there is a connection to a remote BGP speaker whose these connections there is a connection to a remote BGP speaker whose
BGP Identifier equals the one in the OPEN message, and this connec- BGP Identifier equals the one in the OPEN message, and this connec-
tion collides with the connection over which the OPEN message is tion collides with the connection over which the OPEN message is
received then the local system performs the following collision reso- received then the local system performs the following collision reso-
lution procedure: lution procedure:
1. The BGP Identifier of the local system is compared to the BGP 1. The BGP Identifier of the local system is compared to the BGP
Identifier of the remote system (as specified in the OPEN mes- Identifier of the remote system (as specified in the OPEN mes-
sage). Comparing BGP Identifiers is done by treating them as sage). Comparing BGP Identifiers is done by converting them to
(4-octet long) unsigned integers. host byte order and treating them as (4-octet long) unsigned inte-
gers.
2. If the value of the local BGP Identifier is less than the 2. If the value of the local BGP Identifier is less than the
remote one, the local system closes BGP connection that already remote one, the local system closes the BGP connection that
exists (the one that is already in the OpenConfirm state), and already exists (the one that is already in the OpenConfirm state),
accepts BGP connection initiated by the remote system. and accepts the BGP connection initiated by the remote system.
3. Otherwise, the local system closes newly created BGP connection 3. Otherwise, the local system closes newly created BGP connection
(the one associated with the newly received OPEN message), and (the one associated with the newly received OPEN message), and
continues to use the existing one (the one that is already in the continues to use the existing one (the one that is already in the
OpenConfirm state). OpenConfirm state).
Unless allowed via configuration, a connection collision with an Unless allowed via configuration, a connection collision with an
existing BGP connection that is in Established state causes closing existing BGP connection that is in Established state causes closing
of the newly created connection. of the newly created connection.
Note that a connection collision can not be detected with connections Note that a connection collision can not be detected with connections
that are in Idle, or Connect, or Active states. that are in Idle, or Connect, or Active states.
Closing the BGP connection (that results from the collision resolu- Closing the BGP connection (that results from the collision resolu-
tion procedure) is accomplished by sending the NOTIFICATION message tion procedure) is accomplished by sending the NOTIFICATION message
with the Error Code Cease. with the Error Code Cease.
7. BGP Version Negotiation 7. BGP Version Negotiation
BGP speakers may negotiate the version of the protocol by making mul- BGP speakers MAY negotiate the version of the protocol by making mul-
tiple attempts to open a BGP connection, starting with the highest tiple attempts to open a BGP connection, starting with the highest
version number each supports. If an open attempt fails with an Error version number each supports. If an open attempt fails with an Error
Code OPEN Message Error, and an Error Subcode Unsupported Version Code OPEN Message Error, and an Error Subcode Unsupported Version
Number, then the BGP speaker has available the version number it Number, then the BGP speaker has available the version number it
tried, the version number its peer tried, the version number passed tried, the version number its peer tried, the version number passed
by its peer in the NOTIFICATION message, and the version numbers that by its peer in the NOTIFICATION message, and the version numbers that
it supports. If the two peers do support one or more common versions, it supports. If the two peers do support one or more common versions,
then this will allow them to rapidly determine the highest common then this will allow them to rapidly determine the highest common
version. In order to support BGP version negotiation, future versions version. In order to support BGP version negotiation, future versions
of BGP must retain the format of the OPEN and NOTIFICATION messages. of BGP MUST retain the format of the OPEN and NOTIFICATION messages.
8. BGP Finite State machine 8. BGP Finite State machine
This section specifies the BGP operation in terms of a Finite State This section specifies the BGP operation in terms of a Finite State
Machine (FSM). The section falls into 2 parts: Machine (FSM). The section falls into 2 parts:
1) Description of Events for the State machine (section 8.1) 1) Description of Events for the State machine (Section 8.1)
2) Description of the FSM (section 8.2) 2) Description of the FSM (Section 8.2)
Session Attributes required for each connection are; Session Attributes required for each connection are;
1) State 1) State
2) Connect Retry timer 2) Connect Retry timer
3) Hold timer 3) Hold timer
4) Hold time 4) Hold time
5) Keepalive timer 5) Keepalive timer
6) Keepalive time
7) Connect Retry Count
8) Connect Retry Initial Value
The optional Session attributes are listed below. These optional
attributes may be supported either per connection or per local sys-
tem:
1) Delay Open flag
2) Open Delay Timer
3) Perform automatic start flag
4) Perform automatic stop flag
5) Passive TCP establishment flag
6) Perform BGP peer oscillation damping flag
(which will be denoted as stop_peer_flap in text)
7) Idle Hold timer
8) Perform Collision detect in Established flag
9) Accept connections from un-configured peers
10) Track TCP state flag
11) Send NOTIFICATION without an OPEN flag
8.1 Events for the BGP FSM 8.1 Events for the BGP FSM
8.1.1 Administrative Events 8.1.1 Administrative Events
Please note that only Event 1 (manual start) and Event 2 (manual Please note that only Event 1 (manual start) and Event 2 (manual
stop) are mandatory administrative events. All other administrative stop) are mandatory administrative events. All other administrative
events are optional. events are optional. The optional attributes do not have to be sup-
ported. However, if these attributes are supported, the state of the
flags should be as indicated.
Event1: Manual start Event1: Manual start
Definition: Administrator manually starts peer Definition: Local system administrator manually starts peer
connection. connection.
Status: Mandatory Status: Mandatory
Optional
attributes: Passive TCP establishment flag SHOULD not be set.
Event2: Manual stop Event2: Manual stop
Definition: Local system administrator manually Definition: Local system administrator manually
stops the peer connection. stops the peer connection.
Status: Mandatory Status: Mandatory
Event3: Automatic start Event3: Automatic start
Definition: Local system automatically starts the Definition: Local system automatically starts the
BGP connection. BGP connection.
Status: Optional depending on local system Status: Optional depending on local system.
Event4: Manual start with passive TCP establishment Optional
attributes: 1) Perform automatic start flag SHOULD be set.
if this event occurs.
2) if the passive Passive TCP establishment flag
is supported, it SHOULD not be set if this
event occurs.
3) if bgp peer oscillation damping is supported,
the BGP stop_peer_flap flag should not be set
when this event occurs.
Definition: Administrator manually start the peer Event4: Manual start with passive TCP flag
connection, but has the passive flag
enabled. The passive flag indicates Definition: Local system administrator manually starts the peer
connection, but has the passive TCP establishment
enabled. The passive TCP establishment flag indicates
that the peer will listen prior to that the peer will listen prior to
establishing the connection. establishing the connection.
Status: Optional depending on local system Status: Optional depending on local system.
Event5: Automatic start with passive TCP establishment Optional
attributes: 1) Passive TCP Establishment flag SHOULD be set.
if this event occurs.
2) If bgp peer oscilation damping is supported, the
stop_peer_flap falg should not be set when
this event occurs.
Event5: Automatic start with passive TCP flag
Definition: Local system automatically starts the Definition: Local system automatically starts the
BGP connection with the passive flag BGP connection with the passive flag
enabled. The passive flag indicates enabled. The passive flag indicates
that the peer will listen prior to that the peer will listen prior to
establishing a connection. establishing a connection.
Status: Optional depending on local system use Status: Optional depending on local system use
of a passive connection. of a passive connection and automatic start.
Optional
attributes: 1) Perform Automatic start flag SHOULD be set
2) Passive TCP establishment flag SHOULD be set
3) If the bgp peer oscillation flag is supported,
the stop_peer_flap flag SHOULD not be set.
Event6: Automatic start with bgp_stop_flap option set Event6: Automatic start with bgp_stop_flap option set
Definition: Local system automatically starts the Definition: Local system automatically starts the
BGP peer connection with persistent peer BGP peer connection with peer oscillation
oscillation damping enabled. The exact damping enabled. The exact method of damping
method of damping persistent peer persistent peer oscillations is left up to the
oscillations is left up to the implementation, and is outside the scope of
implementation. These methods of this document.
damping persistent BGP adjacency
flapping are outside the scope of this
document.
Status: Optional, used only if the bgp peer has Status: Optional, used only if the bgp peer has enabled
Enabled a method of damping persistent bgp peer oscillation damping enabled with the
BGP peer flapping. optional attribute settings below.
Event7: Auto stop Optional
attributes: 1) Perform automatic start flag SHOULD be set
2) stop_peer_flap flag SHOULD be set
3) Passive TCP establishment flag SHOULD not be set
(cleared).
Event 7: Automatic start with bgp_stop_flap option set and passive
TCP establishment option set
Definition: Local system automatically starts the
BGP peer connection with peer oscillation
damping enabled and passive TCP establishment
enabled. The exact method of damping
persistent peer oscillations is left up to the
implementation, and is outside the scope of
this document.
Status: Optional, used only if the bgp peer has enabled
bgp peer oscillation damping with following optional
flags settings below.
Optional
attributes: 1) Perform automatic start flag SHOULD be set
2) stop_peer_flap flag SHOULD be set
3) Passive TCP establishment flag SHOULD be set
Event8: Automatic stop
Definition: Local system automatically stops the Definition: Local system automatically stops the
BGP connection. BGP connection.
Status: Optional depending on local system An example of an automatic stop event is
exceeding the number of prefixes for a given
8.1.2 Timer Events peer and the local system automatically
disconnecting the peer.
Event8: Idle hold timer expires Status: Optional depending on local system
Definition: Idle Hold timer expires. The Idle Optional
Hold Timer is only used when persistent attributes: 1) Peform automatic stop flag SHOULD Be set
BGP oscillation damping functions are
enabled.
Status: Optional. Used when persistent 8.1.2 Timer Events
BGP peer oscillation damping functions
are enabled.
Event9: Connect retry timer expires Event9: Connect retry timer expires
Definition: An event triggered by the expiration of Definition: An event generated when the Connect Retry timer
the ConnectRetry timer. expires.
Status: Mandatory Status: Mandatory
Event10: Hold time expires Event10: Hold timer expires
Definition: An event generated when the HoldTimer Definition: An event generated when the Hold Timer expires.
expires.
Status: Mandatory Status: Mandatory
Event11: Keepalive timer expires Event11: Keepalive timer expires
Definition: A periodic event generated due to the Definition: An event generated when the Keepalive timer expires.
expiration of the KeepAlive Timer.
Status: Mandatory Status: Mandatory
Event12: DelayBGP open timer expires Event12: Open Delay timer expires
Definition: A timer that delays sending of the BGP Definition: An event generated when the Open Delay timer expires.
Open message for n seconds after the
TCP connection has been completed. Status: Optional
Optional
attributes: If this event occurs,
1) Delay Open flag SHOULD be set
2) Open Delay timer SHOULD be supported
Event13: Idle hold timer expires
Definition: An event generated when the Idle Hold Timer
expires indicating that the session has completed
waiting for a back-off period to prevent bgp peer
oscillation.
The Idle Hold Timer is only used when the persistent
peer oscillation damping function is enabled.
Implementations not implementing the presistent peer
oscillation damping function may not have the Idle Hold
Timer.
Status: Optional Status: Optional
Optional
Attributes: If this event occurs:
1) stop_peer_flap flag SHOULD be set indicating
support for persistent peer oscillation damping
functions,
2) Idle Hold timer should be supported
8.1.3 TCP Connection based Events 8.1.3 TCP Connection based Events
Event13: TCP connection indication & valid remote peer Event14: TCP connection valid indication
Definition: Event indicating that TCP connection Definition: Event indicating the local system reception of
request with a valid source IP address and TCP a TCP connection request with a valid source
port, and valid destination IP address IP address and TCP port, and valid destination
and TCP Port. The definition of IP address and TCP Port. The definition of
invalid source, and invalid destination invalid source, and invalid destination
IP address is left to the implementation. IP address is left to the implementation.
BGP's destination port should be port
BGP's destination port SHOULD be port
179 as defined by IANA. 179 as defined by IANA.
TCP connection request is denoted by TCP connection request is denoted by
the local system receiving a TCP SYN. the local system receiving a TCP SYN.
Status: Mandatory Status: Optional
Event14: RCV TCP connection indication with invalid source or
destination
Definition: TCP connection request received with either Optional
Attributes: 1) The Track TCP state flag SHOULD be set if
this event occurs.
Event15: RCV TCP invalid indication
Definition: Event indicating the local system reception of
a TCP connection request with either
an invalid source address or port an invalid source address or port
number or an invalid destination number or an invalid destination
address or port number. BGP destination address or port number.
port number should be 179 as defined
by IANA.
Again, a TCP connection request is is BGP destination port number SHOULD be 179
as defined by IANA.
Again, a TCP connection request
denoted by local system receiving a TCP denoted by local system receiving a TCP
SYN with an invalid source port or SYN.
destination address or port number.
Status: Mandatory Status: Optional
Event15: TCP connection request sent received an ACK. Optional
Attributes: 1) The Track TCP state should be set if this event
occurs.
Definition: Local system's request to establish a TCP Event16: TCP connection request Acknowledged
connection to the remote side received
an ACK. Definition: Event indicating the Local system's request
to establish a TCP connection to the remote
peer.
The local system's TCP session sent a TCP The local system's TCP session sent a TCP
SYN, and received a TCP SYN, ACK pair of SYN, and received a TCP SYN, ACK messages,
messages, and Sent a TCP ACK. and Sent a TCP ACK.
Status: Mandatory Status: Mandatory
Event16: TCP connection confirmed Event17: TCP connection confirmed
Definition: The local system has received a confirmation that Definition: Event indicates that the local system receiving
the TCP connection has been established by a confirmation that the TCP connection has
the remote site. been established by the remote site.
The remote peer's TCP engine sent a TCP SYN. The remote peer's TCP engine sent a TCP SYN.
The local peer's TCP engine sent a SYN, ACK The local peer's TCP engine sent a SYN, ACK
pair, and now has received a final ACK. message, and now has received a final ACK.
Status: Mandatory Status: Mandatory
Event17: TCP connection fails Event18: TCP connection fails
Definition: This BGP peer receives a TCP Definition: Event indicates that the local system has
connection failure notice. received a TCP connection failure notice.
The remote BGP peer's TCP machine could have The remote BGP peer's TCP machine could have
sent a FIN. The local peer would respond sent a FIN. The local peer would respond
with a FIN-ACK. Another alternative is that with a FIN-ACK. Another alternative is that
the local peer indicated a timeout in the the local peer indicated a timeout in the
TCP session and downed the connection. TCP session and downed the connection.
Status: Mandatory Status: Mandatory
8.1.4 BGP Messages based Events 8.1.4 BGP Messages based Events
Event18: BGPOpen Event19: BGPOpen
Definition: An event indicating that a valid Open Definition: An event is generated when a valid OPEN
message has been received. message has been received.
Status: Mandatory Status: Mandatory
Event19: BGPOpen with BGP Delay Open Timer running optional
attributes: 1) Delay Open flag SHOULD not be set
2) Open Delay timer SHOULD not be running
Definition: An event indicating that a valid Open Event20: BGPOpen with Open Delay Timer running
message has been successful
established for a peer that is Definition: An event is generated when valid OPEN
currently delaying the sending of an message has been received for a peer
BGP Open message. that has a successfully established
transport connection and is currently
delaying the sending of a BGP open
message.
Status: Optional Status: Optional
Event20: BGPHeaderErr Optional
attributes: 1) Delay Open Flag SHOULD be set
2) Open Delay Timer SHOULD be running.
Definition: BGP message header is not valid. Event21: BGPHeaderErr
Definition: An event is generated when a received
BGP message header is not valid.
Status: Mandatory Status: Mandatory
Event21: BGPOpenMsgErr Event22: BGPOpenMsgErr
Definition: An BGP Open message has been received Definition: An event is generated when an OPEN message
with errors. has been received with errors.
Status: Mandatory Status: Mandatory
Event22: Open collision dump Event23: Open collision dump
Definition: An event generated administratively Definition: An event generated administratively
when a connection Collision has been when a connection collision has been
detected while processing an incoming detected while processing an incoming
Open message. This connection has been OPEN message and this connection has been
selected to disconnected. See section selected to disconnected. See Section
6.8 for more information on collision 6.8 for more information on collision
detection. detection.
Event 22 is an administrative could Event23 is an administrative based only
occur if FSM is implemented as two implementation specific policy. This
linked state machines. Event may occur if the FSM is implemented
as two linked state machines.
Status: Optional Status: Optional, depending on local system
Event23: NotifMsgVerErr Optional
Attributes: If the state machine is to process this
attribute in Established state,
1) Peform Collision detect in Established
flag SHOULD be set.
Please note: The Open collision dump can occur
in Idle, Connect, Active, OpenSent, OpenConfirm
without any optional flags being set.
Event24: NotifMsgVerErr
Definition: An event is generated when a Definition: An event is generated when a
NOTIFICIATION message with "version NOTIFICATION message with "version
error" is received. error" is received.
Status: Mandatory Status: Mandatory
Event24: NotifMsg Event25: NotifMsg
Definition: An event is generated when a Definition: An event is generated when a
NOTIFICATION messages is received and NOTIFICATION messages is received and
the error code is anything but the error code is anything but
"version error". "version error".
Status: Mandatory Status: Mandatory
Event25: KeepAliveMsg Event26: KeepAliveMsg
Definition: An event is generated when a KEEPALIVE Definition: An event is generated when a KEEPALIVE
message is received. message is received.
Status: Mandatory Status: Mandatory
Event26: UpdateMsg Event27: UpdateMsg
Definition: An event is generated when a valid Definition: An event is generated when a valid
Update message is received. UPDATE message is received.
Status: Mandatory Status: Mandatory
Event27: UpdateMsgErr Event28: UpdateMsgErr
Definition: An event is generated when an invalid Definition: An event is generated when an invalid
Update message is received. UPDATE message is received.
Status: Mandatory Status: Mandatory
8.2 Description of FSM 8.2 Description of FSM
8.2.1 FSM Definition 8.2.1 FSM Definition
BGP must maintain a separate FSM for each configured peer, Each BGP BGP MUST maintain a separate FSM for each configured peer, Each BGP
peer paired in a potential connection unless configured to remain in peer paired in a potential connection unless configured to remain in
the idle state, or configured to remain passive, will attempt to to the idle state, or configured to remain passive, will attempt to to
connect to the other. For the purpose of this discussion, the active connect to the other. For the purpose of this discussion, the active
or connect side of the TCP connection (the side of a TCP connection or connect side of the TCP connection (the side of a TCP connection
(the side sending the first TCP SYN packet) is called outgoing. The (the side sending the first TCP SYN packet) is called outgoing. The
passive or listening side (the sender of the first SYN ACK) is called passive or listening side (the sender of the first SYN ACK) is called
an incoming connection. [See section on the terms active and passive an incoming connection (see Section 8.2.1.1 on the terms active and
below.] passive below).
A BGP implementation must connect to and listen on TCP port 179 for A BGP implementation MUST connect to and listen on TCP port 179 for
incoming connections in addition to trying to connect to peers. For incoming connections in addition to trying to connect to peers. For
each incoming connection, a state machine must be instantiated. each incoming connection, a state machine MUST be instantiated.
There exists a period in which the identity of the peer on the other There exists a period in which the identity of the peer on the other
end of an incoming connection is known but the BGP identifier is not end of an incoming connection is known but the BGP identifier is not
known. During this time, both an incoming and an outgoing connection known. During this time, both an incoming and an outgoing connection
for the same configured peering may exist. This is referred to as a for the same configured peering may exist. This is referred to as a
connection collision (see Section x.x, was 6.8). connection collision (see Section 6.8).
A BGP implementation will have at most one FSM for each configured A BGP implementation will have at most one FSM for each configured
peering plus one FSM for each incoming TCP connection for which the peering plus one FSM for each incoming TCP connection for which the
peer has not yet been identified. Each FSM corresponds to exactly one peer has not yet been identified. Each FSM corresponds to exactly one
TCP connection. TCP connection.
There may be more than one connections between a pair of peers if the There may be more than one connections between a pair of peers if the
connections are configured to use a different pair of IP addresses. connections are configured to use a different pair of IP addresses.
This is referred to as multiple "configured peerings" to the same This is referred to as multiple "configured peerings" to the same
peer. peer.
skipping to change at page 44, line 12 skipping to change at page 47, line 4
below. When a BGP speaker is configured active it may end up on below. When a BGP speaker is configured active it may end up on
either the active or passive side of the connection that eventually either the active or passive side of the connection that eventually
gets established. Once the TCP connection is completed, it doesn't gets established. Once the TCP connection is completed, it doesn't
matter which end was active and which end was passive and the only matter which end was active and which end was passive and the only
difference is which side of the TCP connection has port number 179. difference is which side of the TCP connection has port number 179.
8.2.1.2 FSM and collision detection 8.2.1.2 FSM and collision detection
There is one FSM per BGP connection. Prior to determining what peer There is one FSM per BGP connection. Prior to determining what peer
a connection is associated with there may be two connections for a a connection is associated with there may be two connections for a
given peer. There should be no more than one connection per peer. given peer. There SHOULD be no more than one connection per peer.
The collision detection identifies the case where there is more than The collision detection identifies the case where there is more than
one connection per peer and provides guidance for which connection to one connection per peer and provides guidance for which connection to
get rid of. When this occurs, the corresponding FSM for the connec- get rid of. When this occurs, the corresponding FSM for the connec-
tion that is closed should be disposed of tion that is closed SHOULD be disposed of.
8.2.1.3 FSM and Optional Attributes
Optional Attributes specify either flags that augment the normal pro-
cessing of the BGP FSM, or optional timers. If a Optional attribute
can be set on a system, the Events and the BGP FSM actions must be
support. For example, if the following options can be set in a BGP
implementation: AutoStart and Passive TCP connection Establishment
flag, then the events 3, 4 and 5 must be supported.
If an Optional attribute is cannot be set (that is declared always
off logically), the events supporting that set of options do not have
to be supported.
8.2.1.4 FSM Event numbers
The Event numbers (1-28) utilized in this state machine description
aid in specifying the behavior of the BGP state machine. Implementa-
tions MAY use these numbers to provide network management informa-
tion.
8.2.2 Finite State Machine 8.2.2 Finite State Machine
Idle state: Idle state:
Initially BGP is in the Idle state. Initially BGP is in the Idle state.
In this state BGP refuses all incoming BGP connections. No In this state BGP refuses all incoming BGP connections. No
resources are allocated to the peer. In response to a resources are allocated to the peer. In response to a
manual start event(Event1) or an automatic start manual start event(Event1) or an automatic start
event(Event3), the local system event(Event3), the local system:
- initializes all BGP resources, - initializes all BGP resources,
- sets ConnectRetryCnt (the connect retry counter) to zero - sets ConnectRetryCnt (the connect retry counter) to zero
- starts the connect retry timer with initial value, - starts the connect retry timer with initial value,
- initiates a TCP connection to the other BGP peer, - initiates a TCP connection to the other BGP peer,
- listens for a connection that may be initiated by - listens for a connection that may be initiated by
the remote BGP peer, and the remote BGP peer, and
- changes its state to connect. - changes its state to Connect.
An manual stop event (Event2) is ignored in the Idle state. An manual stop event (Event2) and Auto stop (Event 8) events are
are ignored in the Idle state.
In response to a manual start event with the passive TCP connection In response to a manual start event with the passive TCP connection
flag (Event 4) or automatic start with the passive TCP connection flag (Event 4) or automatic start with the passive TCP connection
flag (Event 5), the local system: flag (Event 5), the local system:
- initializes all BGP resources, - initializes all BGP resources,
- sets ConnectRetryCnt (the connect retry counter) to zero, - sets ConnectRetryCnt (the connect retry counter) to zero,
- start the connect retry timer with initial value, - starts the connect retry timer with initial value,
- listens for a connection that may be initiated by - listens for a connection that may be initiated by
the remote peer, and the remote peer, and
- changes its state to Active. - changes its state to Active.
The exact value of the ConnectRetry timer is a local The exact value of the ConnectRetry timer is a local
matter, but it should be sufficiently large to allow TCP matter, but it SHOULD be sufficiently large to allow TCP
initialization. initialization.
If a persistent BGP peer oscillation damping function is If the persistent peer oscillation damping function is
enabled, two additional events may occur within Idle state: enabled, three additional events may occur within Idle state:
- Automatic start with bgp_stop_flap set [Event6], - Automatic start with peer_stop_flap set [Event6],
- Idle Hold Timer expired [Event 8]. - Automatic start with peer_stop_flag set [Event7],
- Idle Hold Timer expired [Event 13].
The method of preventing persistent BGP peer oscillation is The method of preventing persistent peer oscillation is
outside the scope of this document. outside the scope of this document.
Any other events [Events 9-27] received in the Idle state, Any other events [Events 9-12, 15-28] received in the Idle state does
are noted by the MIB processing as FSM Errors not cause change in the state of the local system.
and the local peer stays in the Idle State.
Connect State: Connect State:
In this state, BGP is waiting for the TCP connection to In this state, BGP is waiting for the TCP connection to
be completed. be completed.
If the TCP connection succeeds [Event 15 or The start events [Event 1, 3-7] are ignored in connect
Event 16], the local system checks the "Delay Open state.
Flag". If the delay Open flag is set, the local system:
- clears the connect retry timer,
- set the BGP open delay timer to the initial
value.
In response to a manual stop event [Event2], the local system:
- drops the TCP connection,
- releases all BGP resources,
- sets ConnectRetryCnt (the connect retry count) to zero
- resets the connect retry timer (sets to zero), and
- changes its state to Idle.
In response to the connect retry timer expires event [Event
9], the local system:
- drops the TCP connection,
- restarts the connect retry timer,
- stops the Open Delay timer and resets the timer to zero,
- initiates a TCP connection to the other BGP peer,
- continues to listen for a connection that may be
initiated by the remote BGP peer, and
- stays in Connect state.
If the Open Delay timer expires [Event12] in the connect
state, the local system:
- sends an OPEN message to its peer,
- sets the hold timer to a large value, and
- changes its state to OpenSent.
If the BGP port receives a valid TCP connection indication
[Event 14], the TCP connection is processed and
the connection remains in the Connect state.
If the TCP connection receives an invalid indication [Event 15]:
the local system rejects the TCP connection and the connection
remains in the Connect state.
If the TCP connection succeeds [Event 16 or
Event 17], the local system checks the Delay Open flag prior
to processing. If the Delay Open flag is set, the local system:
- clears the connect retry timer,
- set the Open Delay timer to the initial value, and
- stays in the Connect state.
If the Delay Open flag is not set, the local system: If the Delay Open flag is not set, the local system:
- clears the connect retry timer, - clears the connect retry timer,
- completes BGP initialization - completes BGP initialization
- send an Open message to its peer, - sends an OPEN message to its peer,
- sets hold timer to a large value, and - sets hold timer to a large value, and
- Change the state to Open Sent. - changes its state to OpenSent.
A hold timer value of 4 minutes is suggested. A hold timer value of 4 minutes is suggested.
If the Open Delay timer expires [Event 12] in the connect If the TCP connection fails [Event18], the local system checks
state, the Open Delay Timer. If the Open Delay timer is running,
- send an Open message to its peer, the local system:
- set the hold timer to a large value, and - restarts the connect retry time with initial value,
- change the state to Open Sent. - stops the Open Delay timer and resets value to zero,
If the BGP port receives a TCP connection indication
[Event 13], the TCP connection is processed and
the connection remains in the connected state.
If the TCP connection receives an indication
that is invalid or unconfigured. [Event 14]:
- the TCP connection is rejected.
If the TCP connection fails (timeout or disconnect)
[Event17], the local system:
- restarts the connect retry timer,
- continues to listen for a connection that may be - continues to listen for a connection that may be
initiated by the remote BGP peer, and initiated by the remote BGP peer, and
- changes its state to Active. - changes its state to Active.
If the open Delay timer is not running, the local system:
If an Open is received with the BGP Delay Open timer is - resets the connect retry timer (sets to zero), and
running [Event 19], the local system: - Drops the TCP connection,
- Releases all BGP resources,
- and goes to Idle State.
If an OPEN message is received with the Open Delay timer is
running [Event 20], the local system:
- clears the connect retry timer (cleared to zero), - clears the connect retry timer (cleared to zero),
- completes the BGP initialization, - completes the BGP initialization,
- Stops and clears the BGP Open Delay timer - stops and clears the Open Delay timer,
- Sends an Open message - sends an OPEN message,
- Set the hold timer to a large value (4 minutes), and - sends a Keepalive message,
- changes its state to Open Confirm. - If the hold timer value is non-zero,
- start the keepalive timer to inital value,
The start events [Event 1, 3-6] are ignored in connect - reset the hold timer to the negotiated value,
state. else if hold timer value is zero,
- reset the keepalive timer. and
- reset the hold timer value to zero.
- and changes its state to OpenConfirm.
A manual stop event[Event2], the local system: If the value of the autonomous system field is the same as the local
- drops the TCP connection, Autonomous System number, set the connection status to an internal
- releases all BGP resources, connection; otherwise it is "external".
- sets ConnectRetryCnt (the connect retry count) to zero
- resets the connect retry timer (sets to zero), and
- goes to Idle state.
In response to the connect retry timer expired event(Event If BGP message header checking detects an error [Event 21] or
9), the local system: OPEN message checking detects an error [Event 22] (see section
- Sets the MIB FSM error information with connect retry 6.2), the local system:
expired, - (optionally) If the Send Notification without Open flag is set,
- drops the TCP connection then the local system first sends a NOTIFICATION message
- restarts the connect retry timer with the appropriate error code, and then
- initiates a TCP connection to the other BGP
peer,
- continues to listen for a connection that may be
initiated by the remote BGP peer, and
- stays in Connect state.
In response to any other events [Events 7-8, 10-11, 18, 20- - resets the connect retry timer (sets to zero),
27] the local system: - releases all BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1,
- [optionally] performs peer oscillation damping,
- and goes to Idle.
If a NOTIFICATION message is received with a version
error[Event24], the local system checks the Open Delay timer.
If the Open Delay timer is running, the local system:
- resets the connect retry timer (sets to zero), - resets the connect retry timer (sets to zero),
- stops and reset the Open Delay timer (sets to zero),
- releases all BGP resources,
- drops the TCP connection,
- changes its state to Idle.
If the Open Delay timer is not running, the local system:
- resets the connect retry timer (sets to zero),
- releases all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- release all BGP resources,
- increments the ConnectRetryCnt (connect retry count) by 1, - increments the ConnectRetryCnt (connect retry count) by 1,
- [optionally] performs bgp peer oscillation damping, and - optionally performs peer oscillation damping, and
- goes to Idle state. - changes its state to Idle.
In response to any other events [Events 8,10-11,13,19,23,
25-28] the local system:
- if the connect retry timer is running,
stop and reset the connect retry timer (sets to zero),
- if the Delay Open timer is running,
stop and reset the Delay Open timer (sets to zero),
- releases all BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1,
- optionally performs peer oscillation damping, and
- changes its state to Idle.
Active State: Active State:
In this state BGP is trying to acquire a peer by listening In this state BGP is trying to acquire a peer by listening
for and accepting a TCP connection. for and accepting a TCP connection.
A TCP connection succeeds [Event 15 or Event 16], the The start events [Event1, 3-7] are ignored in the Active
local system: process the TCP connection flags state.
- If the BGP delay open flag is set:
A manual stop event[Event2], the local system:
- If the Delay Open timer is running and the
Send NOTIFICATION without Open flag is set,
the local system Sends a NOTIFICATION with a Cease,
- releases all BGP resources including
- stopping the Open delay timer
- drops the TCP connection,
- sets ConnectRetryCnt (connect retry count) to zero
- resets the connect retry timer (sets to zero),
- changes its state to Idle.
In response the ConnectRetry timer expires event[Event9],
the local system:
- restarts the connect retry timer (with initial value),
- initiates a TCP connection to the other BGP peer,
- Continues to listen for TCP connection that may be
initiated by remote BGP peer,
- and changes its state to Connect.
If the local system has the Open Delay timer expired
[Event12], the local system:
- clears the connect retry timer (set to zero),
- stops and clears the Open Delay timer (set to zero),
- completes the BGP initialization,
- sends the OPEN message to it's remote peer,
- sets its hold timer to a large value, and
- changes its state to OpenSent.
A hold timer value of 4 minutes is also suggested for this
state transition.
If the local system receives a valid TCP indication
[Event 14], the local system processes the TCP connection
flags, and stays in Active state.
If the local system receives an invalid TCP indication [Event 15]:
the local system rejects the TCP connection, and stays in
the Active State.
A TCP connection succeeds [Event 16 or Event 17], the
local system checks the "Delay Open Flag" prior to
processing. If the Delay Open flag is set, the local system
o clears the connect retry timer, o clears the connect retry timer,
o completes the BGP initialization, and o sets the BGP Open Delay timer to the initial value, and
o sets the BGP delay Open timer o stays in the Active state.
- If the BGP delay open flag is not set: -If the Delay Open flag is not set, the local system
o clears the connect retry timer, o clears the connect retry timer,
o completes the BGP initialization, o completes the BGP initialization,
o sends the Open message to it's peer, o sends the OPEN message to it's peer,
o sets its hold timer to a large value, o sets its hold timer to a large value, and
and changes its state to OpenSent. o changes its state to OpenSent.
A Hold timer value of 4 minutes is suggested.
If the local system receives a valid TCP Indication
[Event 13], the local system processes the TCP connection flags.
If the local system receives a TCP indication A hold timer value of 4 minutes is suggested as a "large value" for
that is invalid for this connection [Event 14]: the hold timer.
- the TCP connection is rejected.
If the local system receives a TCP connection If the local system receives a TCP connection fails event [Event 18],
failed [Event 17] (timeout or receives connection the local system will:
disconnect), the local system will: - restart connect retry timer (with initial value),
- set TCP disconnect in the MIB reason code, - stops and clears Open Delay Timer (sets the value to zero),
- restart connect retry timer (with initial value)
- release all BGP resources - release all BGP resources
- Acknowledge the drop of TCP connection if - Acknowledge the drop of TCP connection if
TCP disconnect (send a FIN ACK), TCP disconnect (send a FIN ACK),
- Increment ConnectRetryCnt (connect retry count) by 1, and - Increment ConnectRetryCnt (connect retry count) by 1, and
- perform the BGP peer oscillation damping process [2]. - optionally perform peer oscillation damping,
- and go to to Idle.
If the local system has the delay open timer expired [event
12] local system:
- clears the connect retry timer (set to zero),
- stops and clears the delay open timer (set to zero)
- completes the BGP initialization,
- sends the Open message to it's remote peer,
- sets its hold timer to a large value,
- and set the state to Open Confirm.
A hold timer value of 4 minutes is also suggested for this
state transition.
If an Open is received with the BGP delay open timer is If an OPEN message is received with the Open Delay timer is
running [Event 19], the local system running [Event 20], the local system
- clears the connect retry timer (cleared to zero), - clears the connect retry timer (cleared to zero),
- stops and clears the BGP open delay timer - stops and clears the Open Delay timer
- completes the BGP initialization, - completes the BGP initialization,
- stops and clears the BGP open delay timer - sends an OPEN message,
- sends an Open message - send a Keepalive message, and
- set its hold timer to a large value (4 minutes), and - if the hold timer value is non-zero,
- starts the keepalive timer to initial value,
- resets the hold timer to the negotiated value,
else if the hold timer is zero
- resets the keepalive timer (set to zero),
- resets the hold timer to zero.
- changes its state to Open Confirm. - changes its state to Open Confirm.
In response the ConnectRetry timer expired event[Event9], If the value of the autonomous system field is the same as the local
the local system: Autonomous System number, set the connection status to an internal
- restarts the connect retry timer (with initial value), connection; otherwise it is "external".
- initiates a TCP connection to the other BGP
peer,
- Continues to listen for TCP connection that may be
initiated by remote BGP peer,
- and changes its state to Connect.
The start events [Event1, 3-6] are ignored in the Active If BGP message header checking detects an error [Event 21] or OPEN
state. message checking detects an error [Event 22] (see section 6.2), the
local system:
- (optionally) sends NOTIFICATION message with the
appropriate error code,
- resets the connect retry timer (sets to zero),
- releases all BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1,
- [optionally] performs peer oscillation damping,
- and goes to Idle.
A manual stop event[Event2], the local system: If a NOTIFICATION message is received with a version
- Sets the administrative down in the MIB reason code, error[Event24], the local system checks the Open Delay timer.
- Sends a Notification with a Cease, If the Open Delay timer is running, the local system:
- If any BGP routes exist, delete the routes - resets the connect retry timer (sets to zero),
- release all BGP resources, - stops and reset the Open Delay timer (sets to zero,
- releases all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- sets ConnectRetryCnt (connect retry count) to zero - changes its state to Idle.
If the Open Delay timer is not running, the local system:
- resets the connect retry timer (sets to zero), - resets the connect retry timer (sets to zero),
- goes to Idle state. - releases all BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1,
- optionally performs peer oscillation damping, and
- changes its state to Idle
In response to any other event (Events 7-8, 10-11,18, 20- In response to any other event [Events 8,10-11,13,19,23,25-28],
27), the local system: the local system:
- stores the MIB information to indicate appropriate - resets the connect retry timer (sets to zero),
error [FSM for Events 7-8, 10-11, 18, 20-27]
- reset the connect retry timer (sets to zero),
- release all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- releases all BGP resources,
- increments the ConnectRetryCnt (connect retry count) by one, - increments the ConnectRetryCnt (connect retry count) by one,
- optionally performs BGP peer oscillation damping, - optionally performs peer oscillation damping, and
- and goes to the idle state - changes its state to Idle.
Open Sent: Open Sent:
In this state BGP waits for an Open Message from its peer. In this state BGP waits for an OPEN message from its peer.
When an OPEN message is received, all fields are checked
for correctness. If there are no errors in the OPEN message
[Event 18] the local system:
- resets the BGP Delay timer to zero,
- reset BGP Connect Timer to zero,
- sends a KEEPALIVE message and
- sets a KeepAlive timer (via the text below)
- sets the Hold timer according to the negotiated value
(see section 4.2), and
- sets the state to Open Confirm.
If the negotiated Hold time value is zero, then the Hold
and KeepAlive timers are not started. If the
value of the Autonomous System field is the same as the
local Autonomous System number, then the connection is an
"internal" connection; otherwise, it is an "external"
connection. (This will impact UPDATE processing as
described below.)
If the BGP message header checking [Event20] or OPEN message
check detects an error (see Section 6.2)[Event21], the local system:
- sends a NOTIFICATION message with appropriate error
code,
- reset the connect retry timer (sets to zero),
- if there are any routes associated with the BGP session,
delete these routes
- release all BGP resources,
- drop the TCP connection
- increments the ConnectRetryCnt (connect retry cout) by 1,
- bgp peer oscillation damping process,
- and goes to the Idle state.
Collision detection mechanisms (section 6.8) need to be
applied when a valid BGP Open is received [Event 18 or
Event 19]. Please refer to section 6.8 for the details of
the comparison. An administrative collision detect is when
BGP implementation determines my means outside the scope of
this document that a connection collision has occurred.
If a connection in Open Sent is determined to be the
connection that must be closed, an administrative collision
detect [Event 22] is signaled to the state machine. If such
an administrative collision detect dump [Event 22] is
received in Open Sent, the local system:
- sets MIB state information to
collision detect closure,
- send a NOTIFICATION with a CEASE
- resets the connect retry timer,
- release all BGP resources,
- drop the TCP connection,
- increments ConnectRetryCnt (connect rery count) by 1,
- performs any BGP peer oscillation damp process, and
- enters Idle state.
If a NOTIFICATION message is received with a version
error[Event23], Notification message without version number
[Event 24], the local system:
- resets the connect retry timer (sets to zero)
- drops the TCP connection,
- releases all BGP resources,
- increments the ConnectRetryCnt (connect retry count) by 1
- process any BGP peer oscillation damping,
- and sets the state to Idle.
The Start events [Event1, 3-6] are ignored in the OpenSent The Start events [Event1, 3-7] are ignored in the OpenSent
state. state.
If a manual stop event [Event 2] is issued in Open sent If a manual stop event [Event 2] is issued in Open sent
state, the local system: state, the local system:
- Sets administrative down reason in MIB reason, - sends the NOTIFICATION with a cease,
- sends the Notification with a cease, - release all BGP resources,
- if BGP routes exists, delete the routes, - drops the TCP connection,
- Release all BGP resources,
- Drops the TCP connection,
- set ConnectRetryCnt (connect retry count) to zero, - set ConnectRetryCnt (connect retry count) to zero,
- resets the Connect Retry timer (set to zero), and - resets the Connect Retry timer (set to zero), and
- transitions to the Idle state. - changes its state to Idle.
If an automatic stop event [Event 7] is issued in Open sent If an automatic stop event [Event 8] is issued in OpenSent
state, the local system: state, the local system:
- Sets administrative down reason in MIB reason, - sends the NOTIFICATION with a cease,
- sends the Notification with a cease,
- if any routes are associated with te BGP session,
delete the routes,
- release all the BGP resources - release all the BGP resources
- Drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1, - increments the ConnectRetryCnt (connect retry count) by 1,
- BGP peer oscillation process [2], and - optionally performs peer oscillation damping, and
- transitions to the Idle state. - changes its state to Idle.
If the Hold Timer expires[Event 10], the local system: If the Hold Timer expires[Event 10], the local system:
- set Hold timer expired in MIB Error reason code,
- send a NOTIFICATION message with error code Hold - send a NOTIFICATION message with error code Hold
Timer Expired, Timer Expired,
- reset the connect retry timer (sets to zero), - reset the connect retry timer (sets to zero),
- releases all BGP resources, - releases all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1, - increments the ConnectRetryCnt (connect retry count) by 1, and
and transitions to the Idle state. - changes its state to Idle.
If a TCP indication is received for valid connection If a TCP indication is received for valid connection
[Event 13] or TCP request aknowledgement [Event 15] [Event 14] or TCP request aknowledgement [Event 16]
is received, or a TCP connect confirm [Event 16] is is received, or a TCP connect confirm [Event 17] is
received a second TCP session may be in progress. This received a second TCP session may be in progress. This
second TCP session is tracked per the Call Collision second TCP session is tracked per the Connection Collision
processing (section 6.8) until an OPEN message is received. processing (Section 6.8) until an OPEN message is received.
A TCP connection for an invalid port [Event 14] is ignored. A TCP connection for an invalid port [Event 15] is ignored.
If a TCP connection failure [Event17], is received If a TCP connection fails event [Event18] indication is received
the local system: the local system:
- closes the BGP connection, - closes the BGP connection,
- restarts the Connect Retry timer, - restarts the Connect Retry timer,
- and continues to listen for a connection that may be - continues to listen for a connection that may be
initiated by the remote BGP peer, initiated by the remote BGP peer, and
- and goes into Active state. - changes its state to Active.
In response to any other event [Events 8-9, 11-12, 19, 25-27], When an OPEN message is received, all fields are checked
for correctness. If there are no errors in the OPEN message
[Event 19] the local system:
- resets the Open Delay timer to zero,
- reset BGP Connect Timer to zero,
- sends a KEEPALIVE message and
- sets a KeepAlive timer (via the text below)
- sets the hold timer according to the negotiated value
(see Section 4.2), and
- changes its state to OpenConfirm.
If the negotiated hold time value is zero, then the Hold and
KeepAlive timers are not started. If the value of the Autonomous
System field is the same as the local Autonomous System number,
then the connection is an "internal" connection; otherwise, it
is an "external" connection. (This will impact UPDATE processing
as described below.)
If the BGP message header checking [Event21] or OPEN message
check detects an error (see Section 6.2)[Event22], the local system:
- sends a NOTIFICATION message with appropriate error
code,
- resets the connect retry timer (sets to zero),
- releases all BGP resources,
- drops the TCP connection
- increments the ConnectRetryCnt (connect retry cout) by 1,
- optionally performs peer oscillation damping, and
- changes its state to Idle.
Collision detection mechanisms (Section 6.8) need to be
applied when a valid BGP OPEN message is received [Event 19 or
Event 20]. Please refer to Section 6.8 for the details of
the comparison. An administrative collision detect is when
BGP implementation determines my means outside the scope of
this document that a connection collision has occurred.
If a connection in OpenSent is determined to be the
connection that must be closed, an open collision dump [Event 23]
is signaled to the state machine. If such an event is
received in OpenSent, the local system:
- sends a NOTIFICATION with a Cease
- resets the connect retry timer,
- releases all BGP resources,
- drops the TCP connection,
- increments ConnectRetryCnt (connect rery count) by 1,
- optionally performs peer oscillation damping, and
- changes its state to Idle.
If a NOTIFICATION message is received with a version
error[Event24], the local system:
- resets the connect retry timer (sets to zero)
- releases all BGP resources,
- drops the TCP connection,
- changes its state to Idle.
In response to any other event [Events 9, 11-13,20,25-28],
the local system: the local system:
- sends the NOTIFICATION with the Error Code Finite - sends the NOTIFICATION with the Error Code Finite
state machine error, state machine error,
- resets the connect retry timer (sets to zero), - resets the connect retry timer (sets to zero),
- releases all BGP resources - releases all BGP resources
- drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1, - increments the ConnectRetryCnt (connect retry count) by 1,
- process any bgp peer oscillation damping[2], - optionally performs peer oscillation damping, and
- and sets the state to idle. - changes its state to Idle.
Open Confirm State: Open Confirm State:
In this state BGP waits for a KEEPALIVE or NOTIFICATION In this state BGP waits for a KEEPALIVE or NOTIFICATION
message. message.
If the local system receives a KEEPALIVE message[Event 25], Any start event [Event1, 3-7] is ignored in the OpenConfirm
- restarts the Hold timer, and
- changes its state to Established.
If the local system receives a NOTIFICATION message [Event
23-24] or receives a TCP Disconnect [Event 17] from the
underlying TCP , the local system:
- sets the appropriate MIB information for FSM error,
- resets the connect retry timer (sets the timer to
zero),
- releases all BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1,
- and sets the state to idle.
Any start event [Event1, 3-6] is ignored in the OpenConfirm
state. state.
In response to a manual stop event[Event 2] initiated by In response to a manual stop event[Event 2] initiated by
the operator, the local system: the operator, the local system:
- set Administrative down in MIB Reason code,
- sends the NOTIFICATION message with Cease, - sends the NOTIFICATION message with Cease,
- if any BGP routes, dete the routes
- releases all BGP resources, - releases all BGP resources,
- drop the TCP connection, - drop the TCP connection,
- sets the ConnectRetryCnt (connect retry count) to zero - sets the ConnectRetryCnt (connect retry count) to zero
- sets the connect retry timer to zero, and - sets the connect retry timer to zero, and
- transitions to Idle state. - changes its state to Idle.
In response to the Automatic stop event initiated by the In response to the Automatic stop event initiated by the
system[Event 7], the local system: system[Event 8], the local system:
- sets the MIB entry for this peer to administratively
down,
- sends the NOTIFICATION message with Cease, - sends the NOTIFICATION message with Cease,
- connect retry timer reset (set to zero) - connect retry timer reset (set to zero)
- If any BGP routes exist, delete the routes,
- release all BGP resources, - release all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) - increments the ConnectRetryCnt (connect retry count)
by 1, and by 1,
- transitions to the Idle State. - optionally performs peer oscillation damping,
- changes its state to Idle.
If the Hold Timer expires before a KEEPALIVE message is If the Hold Timer expires before a KEEPALIVE message is
received [Event 10], the local system: received [Event 10], the local system:
- set the MIB reason to Hold time expired,
- send the NOTIFICATION message with the error code - send the NOTIFICATION message with the error code
set to Hold Time Expired, set to Hold Time Expired,
- resets the connect retry timer (sets the timer to to - resets the connect retry timer (sets the timer to to
zero), zero),
- releases all BGP resources, - releases all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1, - increments the ConnectRetryCnt (connect retry count)
- and sets the state to Idle. by 1,
- optionally performs peer oscillation damping,
and
- changes its state to Idle.
If the local system receives a KEEPALIVE timer expires If the local system receives a KEEPALIVE timer expires
event [Event 11], the system: event [Event 11], the system:
- sends a KEEPALIVE message, - sends a KEEPALIVE message,
- restarts the Keepalive timer, and - restarts the Keepalive timer, and
- remains in Open Confirmed state. - remains in Open Confirmed state.
In the event of TCP establishment [Event 13], or TCP In the event of TCP connection valid indication [Event 14], or TCP
connection succeeding [Event 15 or Event 16] while in Open connection succeeding [Event 16 or Event 17] while in OpenConfirm,
Confirm, the local system needs to track the 2nd the local system needs to track the 2nd connection.
connection.
If a TCP connection is attempted to an invalid port [Event If a TCP connection is attempted to an invalid port [Event
14], the local system will ignore the second connection 15], the local system will ignore the second connection
attempt. attempt.
If an OPEN message is received, all fields are check for If the local system receives a TCP connection fails event
correctness. If the BGP message header checking [Event20] [Event 18] from the underlying TCP. or a NOTIFICATION
or OPEN message check detects an error (see Section message [Event 25] the local system:
6.2)[Event21], the local system:
- sends a NOTIFICATION message with appropriate error
code,
- resets the connect retry timer (sets the timer to - resets the connect retry timer (sets the timer to
zero), zero),
- releases all BGP resources, - releases all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1, - increments the ConnectRetryCnt (connect retry count)
- runs the BGP peer oscillation damping process [2] by 1,
- and goes to the Idle state. - optionally performs peer oscillation damping,
- changes its state to Idle.
If the Open messages is valid [Event 18], the collision If the local system receives a NOTIFICATION message [Event 24] with
detect function is processed per section 6.8. If this a version error, the local system:
connection is to be dropped due to call collision, the - resets the connect retry timer (sets the timer to zero),
- releases all BGP resources,
- drops the TCP connection,
- changes its state to Idle. [Verify this/or above]
If the OPEN message is valid [Event 19], the collision
detect function is processed per Section 6.8. If this
connection is to be dropped due to connection collision, the
local system: local system:
- sets the Call Collision cease in the MIB reason - sends a NOTIFICATION with a Cease
code,
- sends a Notification with a Cease
- resets the Connect timer (set to zero), - resets the Connect timer (set to zero),
- releases all BGP resources, - releases all BGP resources,
- Drops the TCP connection (send TCP FIN), - drops the TCP connection (send TCP FIN),
- increments the ConnectRetryCnt by 1 (connect retry count), and - increments the ConnectRetryCnt by 1 (connect retry count), and
- performs any BGP peer oscillation damping process [2]. - optionally performs peer oscillation damping.
If during the processing of another Open message, the BGP If an OPEN message is received, all fields are check for
correctness. If the BGP message header checking [Event21]
or OPEN message check detects an error (see Section
6.2)[Event22], the local system:
- sends a NOTIFICATION message with appropriate error
code,
- resets the connect retry timer (sets the timer to
zero),
- releases all BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1,
- optionally performs peer oscillation damping, and
- changes its state to Idle.
If during the processing of another OPEN message, the BGP
implementation determines my means outside the scope of implementation determines my means outside the scope of
this document that a connection collision has occurred and this document that a connection collision has occurred and
this connection is to be closed, the local system will this connection is to be closed, the local system will
issue a call collision dump [Event 22]. When the local issue a open collision dump [Event 23]. When the local
system receives a call collision dump event [Event 22], the system receives a open collision dump event [Event 23], the
local system: local system:
- Sets the MIB FSM variable to indicate collision - send a NOTIFICATION with a Cease
detected and dump connection.
- send a NOTIFICATION with a CEASE
- deletes all routes associated with connection,
- resets the connect retry timer, - resets the connect retry timer,
- releases all BGP resources - releases all BGP resources
- drops all TCP connection, - drops all TCP connection,
- increments the ConnectRetryCnt (connect retry count) by 1, - increments the ConnectRetryCnt (connect retry count) by 1,
- and performs any BGP peer oscillation damping, and - optionally performs peer oscillation damping, and
- enters Idle state. - changes its state to Idle.
In response to any other event [Events 8-9, 12, 19, 26-27], If the local system receives a KEEPALIVE message[Event 26],
- restarts the Hold timer, and
- changes its state to Established.
In response to any other event [Events 9, 12-13, 27-28],
the local system: the local system:
- sends a NOTIFICATION with a code of Finite State - sends a NOTIFICATION with a code of Finite State
Machine Error, Machine Error,
- resets the connect retry timer (sets to zero) - resets the connect retry timer (sets to zero)
- drops the TCP connection,
- releases all BGP resources, - releases all BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retrycount) by 1, - increments the ConnectRetryCnt (connect retrycount) by 1,
- performs any BGP peer oscillation damping, and - optionally performs peer oscillation damping, and
- transitions to Idle state. - changes its state to Idle.
Established State: Established State:
In the Established state BGP can exchange UPDATE, In the Established state BGP can exchange UPDATE,
NOTFICATION, and KEEPALIVE messages with its peer. NOTFICATION, and KEEPALIVE messages with its peer.
If the local system receives an UPDATE message [Event26], Any start event (Event 1, 3-7) is ignored in the
the local system will:
- process the update packet
- restarts its Hold timer, if the negotiated Hold Time
value is non-zero, and
- remain in the Established state.
If the local system receives a NOTIFICATION message
[Event23 or Event24] or a disconnect [Event17] from the
underlying TCP, it:
- sets the appropriate error code in MIB reason code,
- if any BGP routes exist, delete all BGP routes,
- resets the connect retry timer (sets to zero),
- releases all the BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count)
by 1, and
- goes to the Idle state.
If the local system receives a Keepalive message
[Event 25], the local system will:
- restarts its Hold Timer, if the negotiated Hold Time
value is non-zero, and
- remain in the Established state.
If the local system receives an UPDATE message, and the
Update message error handling procedure (see Section 6.3)
detects an error [Event27], the local system:
- sends a NOTIFICATION message with Update error,
- resets the connect retry timer (sets to zero),
- drops the TCP connection,
- releases all BGP resources,
- increments the ConnectRetryCnt (connect retry count)
by 1,
- performs any BGP peer oscillation damping,
- and goes to Idle state.
Any start event (Event 1, 3-6) is ignored in the
Established state. Established state.
In response to a manual stop event (initiated by an In response to a manual stop event (initiated by an
operator)[Event2], the local sytem: operator)[Event2], the local sytem:
- sets the Administrative stop in MIB reason code,
- sends the NOTIFICATION message with Cease, - sends the NOTIFICATION message with Cease,
- if BGP routes exist, delete the BGP routes, - resets the connect retry timer to zero (0),
- delete all routes associated with this connection,
- release BGP resources, - release BGP resources,
- drops TCP connection, - drops TCP connection,
- sets ConnectRetryCnt (connect retry count) - sets ConnectRetryCnt (connect retry count)
to zero (0), to zero (0), and
- resets connect retry timer to zero (0), and - changes its state to Idle.
- transitions to the Idle.
In response to an automatic stop event initiated by the In response to an automatic stop event initiated by the
system (automatic) [Event7], the local system: system (automatic) [Event8], the local system:
- sets Administrative Stop in MIB Reason code,
- sends a NOTIFICATION with Cease, - sends a NOTIFICATION with Cease,
- resets the connect retry timer (sets to zero) - resets the connect retry timer (sets to zero)
- deletes all routes associated with bgp connection, - deletes all routes associated with this connection,
- releases all BGP resources, - releases all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) - increments the ConnectRetryCnt (connect retry count)
by 1, by 1,
- performs any BGP peer oscillation damping, and - optionally performs peer oscillation damping, and
- transitions to the idle state. - changes its state to Idle.
An example automatic stop event is exceeding the number of An example automatic stop event is exceeding the number of
prefixes for a given peer and the local system prefixes for a given peer and the local system
automatically disconnecting the peer. automatically disconnecting the peer.
If the Hold timer expires [Event10], the local system: If the Hold timer expires [Event10], the local system:
- sends a NOTIFICATION message with Error Code Hold - sends a NOTIFICATION message with Error Code Hold
Timer Expired, Timer Expired,
- resets the connect retry timer (sets to zero), - resets the connect retry timer (sets to zero),
- releases all BGP resources, - releases all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) - increments the ConnectRetryCnt (connect retry count)
by 1, by 1,
- performs any BGP peer oscillation damping, - optionally performs peer oscillation damping, and
- and goes to Idle state. - changes its state to Idle.
If the KeepAlive timer expires [Event11], the local system If the KeepAlive timer expires [Event11], the local system
sends a KEEPALIVE message, it restarts its KeepAlive timer, sends a KEEPALIVE message, it restarts its KeepAlive timer,
unless the negotiated Hold Time value is zero. unless the negotiated Hold Time value is zero.
Each time time the local system sends a KEEPALIVE or UPDATE Each time time the local system sends a KEEPALIVE or UPDATE
message, it restarts its KeepAlive timer, unless the message, it restarts its KeepAlive timer, unless the
negotiated Hold Time value is zero. negotiated Hold Time value is zero.
A TCP connection indication [Event 13] received A TCP connection indication [Event 14] received
for a valid port will cause the 2nd connection to be for a valid port will cause the 2nd connection to be
tracked. A TCP connection indications for tracked.
invalid port [Event 14], will be ignored.
In response to a TCP connection succeeds [Event 15 A TCP connection indications for invalid port [Event 15],
or Event 16], the 2nd connection shall be tracked until will be ignored.
In response to a TCP connection succeeds [Event 16
or Event 17], the 2nd connection SHALL be tracked until
it sends an OPEN message. it sends an OPEN message.
If a valid Open message [Event 18] is received, it will be If a valid OPEN message [Event 19] is received, it will be
checked to see if it collides (section 6.8) with any other checked to see if it collides (Section 6.8) with any other
session. If the BGP implementation determines that this session. If the BGP implementation determines that this
connection needs to be terminated, it will process an Call connection needs to be terminated, it will process an open
Collision dump event[Event 22]. If this session needs to be collision dump event[Event 23]. If this session needs to be
terminated, the connection will be terminated by: terminated, the connection will be terminated by:
- send a NOTIFICATION with a CEASE - send a NOTIFICATION with a Cease,
- deletes all routes associated with connection, - resets the connect retry time (sets to zero),
- resets the connect retry timer, - deletes all routes associated with this connection,
- if any BGP routes, delete the routes,
- release all BGP resources, - release all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- increments ConnectRetryCnt (connect retry count) - increments ConnectRetryCnt (connect retry count)
by 1, by 1,
- and performs any BGP peer oscillation damping, - optionally performs peer oscillation damping, and
- and enters the Idle state - changes its state to Idle.
In response to any other event [Events 8-9,12, 19-21] the If the local system receives a NOTIFICATION message
[Event24 or Event 25] or a TCP connections fails [Event18]
from the underlying TCP, it:
- resets the connect retry timer (sets to zero),
- delete all routes associated with this connection,
- releases all the BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count)
by 1, and
- changes its state to Idle.
If the local system receives a KEEPALIVE message
[Event 26], the local system will:
- restarts its Hold Timer, if the negotiated Hold Time
value is non-zero, and
- remain in the Established state.
If the local system receives an UPDATE message [Event27],
the local system will:
- process the update packet
- restarts its Hold timer, if the negotiated Hold Time
value is non-zero, and
- remain in the Established state.
If the local system receives an UPDATE message, and the
UPDATE message error handling procedure (see Section 6.3)
detects an error [Event28], the local system:
- sends a NOTIFICATION message with Update error,
- resets the connect retry timer (sets to zero),
- delets all routes associated with this connection,
- releases all BGP resources,
- drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count)
by 1,
- optionally performs peer oscillation damping, and
- changes its state to Idle.
In response to any other event [Events 9, 12-13, 20-22] the
local system: local system:
- sends a NOTIFICATION message with Error Code Finite - sends a NOTIFICATION message with Error Code Finite
State Machine Error, State Machine Error,
- deletes all routes associated with BGP connection, - deletes all routes associated with this connection,
- resets the connect retry timer (sets to zero) - resets the connect retry timer (sets to zero)
- releases all BGP resources, - releases all BGP resources,
- drops the TCP connection, - drops the TCP connection,
- increments the ConnectRetryCnt (connect retry count) - increments the ConnectRetryCnt (connect retry count)
by 1, by 1,
- performs any BGP peer oscillation damping, and - optionally performs peer oscillation damping, and
- transitions to Idle. - changes its state to Idle.
9. UPDATE Message Handling 9. UPDATE Message Handling
An UPDATE message may be received only in the Established state. An UPDATE message may be received only in the Established state.
When an UPDATE message is received, each field is checked for valid- When an UPDATE message is received, each field is checked for valid-
ity as specified in Section 6.3. ity as specified in Section 6.3.
If an optional non-transitive attribute is unrecognized, it is qui- If an optional non-transitive attribute is unrecognized, it is qui-
etly ignored. If an optional transitive attribute is unrecognized, etly ignored. If an optional transitive attribute is unrecognized,
the Partial bit (the third high-order bit) in the attribute flags the Partial bit (the third high-order bit) in the attribute flags
octet is set to 1, and the attribute is retained for propagation to octet is set to 1, and the attribute is retained for propagation to
other BGP speakers. other BGP speakers.
If an optional attribute is recognized, and has a valid value, then, If an optional attribute is recognized, and has a valid value, then,
depending on the type of the optional attribute, it is processed depending on the type of the optional attribute, it is processed
locally, retained, and updated, if necessary, for possible propaga- locally, retained, and updated, if necessary, for possible propaga-
tion to other BGP speakers. tion to other BGP speakers.
The information carried by the AS_PATH attribute is checked for AS
loops. AS loop detection is done by scanning the full AS path (as
specified in the AS_PATH attribute), and checking that the autonomous
system number of the local system does not appear in the AS path. If
the autonomous system number appears in the AS path the route may be
stored in the Adj-RIB-In, but unless the router is configured to
accept routes with its own autonomous system in the AS path, the
route shall not be passed to the BGP Decision Process. Operations of
a router that is configured to accept routes with its own autonomous
system number in the AS path are outside the scope of this document.
If the UPDATE message contains a non-empty WITHDRAWN ROUTES field, If the UPDATE message contains a non-empty WITHDRAWN ROUTES field,
the previously advertised routes whose destinations (expressed as IP the previously advertised routes whose destinations (expressed as IP
prefixes) contained in this field shall be removed from the Adj-RIB- prefixes) contained in this field SHALL be removed from the Adj-RIB-
In. This BGP speaker shall run its Decision Process since the previ- In. This BGP speaker SHALL run its Decision Process since the previ-
ously advertised route is no longer available for use. ously advertised route is no longer available for use.
If the UPDATE message contains a feasible route, the Adj-RIB-In will If the UPDATE message contains a feasible route, the Adj-RIB-In will
be updated with this route as follows: if the NLRI of the new route be updated with this route as follows: if the NLRI of the new route
is identical to the one of the route currently stored in the Adj-RIB- is identical to the one of the route currently stored in the Adj-RIB-
In, then the new route shall replace the older route in the Adj-RIB- In, then the new route SHALL replace the older route in the Adj-RIB-
In, thus implicitly withdrawing the older route from service. Other- In, thus implicitly withdrawing the older route from service. Other-
wise, if the Adj-RIB-In has no route with NLRI identical to the new wise, if the Adj-RIB-In has no route with NLRI identical to the new
route, the new route shall be placed in the Adj-RIB-In. route, the new route SHALL be placed in the Adj-RIB-In.
Once the BGP speaker updates the Adj-RIB-In, the speaker shall run Once the BGP speaker updates the Adj-RIB-In, the speaker SHALL run
its Decision Process. its Decision Process.
9.1 Decision Process 9.1 Decision Process
The Decision Process selects routes for subsequent advertisement by The Decision Process selects routes for subsequent advertisement by
applying the policies in the local Policy Information Base (PIB) to applying the policies in the local Policy Information Base (PIB) to
the routes stored in its Adj-RIBs-In. The output of the Decision Pro- the routes stored in its Adj-RIBs-In. The output of the Decision Pro-
cess is the set of routes that will be advertised to all peers; the cess is the set of routes that will be advertised to peers; the
selected routes will be stored in the local speaker's Adj-RIB-Out. selected routes will be stored in the local speaker's Adj-RIB-Out
according to policy.
The selection process is formalized by defining a function that takes The selection process is formalized by defining a function that takes
the attribute of a given route as an argument and returns either (a) the attribute of a given route as an argument and returns either (a)
a non-negative integer denoting the degree of preference for the a non-negative integer denoting the degree of preference for the
route, or (b) a value denoting that this route is ineligible to be route, or (b) a value denoting that this route is ineligible to be
installed in LocRib and will be excluded from the next phase of route installed in LocRib and will be excluded from the next phase of route
selection. selection.
The function that calculates the degree of preference for a given The function that calculates the degree of preference for a given
route shall not use as its inputs any of the following: the existence route SHALL NOT use as its inputs any of the following: the existence
of other routes, the non-existence of other routes, or the path of other routes, the non-existence of other routes, or the path
attributes of other routes. Route selection then consists of individ- attributes of other routes. Route selection then consists of individ-
ual application of the degree of preference function to each feasible ual application of the degree of preference function to each feasible
route, followed by the choice of the one with the highest degree of route, followed by the choice of the one with the highest degree of
preference. preference.
The Decision Process operates on routes contained in the Adj-RIB-In, The Decision Process operates on routes contained in the Adj-RIB-In,
and is responsible for: and is responsible for:
- selection of routes to be used locally by the speaker - selection of routes to be used locally by the speaker
skipping to change at page 59, line 44 skipping to change at page 64, line 25
the Loc-RIB. the Loc-RIB.
c) Phase 3 is invoked after the Loc-RIB has been modified. It is c) Phase 3 is invoked after the Loc-RIB has been modified. It is
responsible for disseminating routes in the Loc-RIB to each peer, responsible for disseminating routes in the Loc-RIB to each peer,
according to the policies contained in the PIB. Route aggregation according to the policies contained in the PIB. Route aggregation
and information reduction can optionally be performed within this and information reduction can optionally be performed within this
phase. phase.
9.1.1 Phase 1: Calculation of Degree of Preference 9.1.1 Phase 1: Calculation of Degree of Preference
The Phase 1 decision function shall be invoked whenever the local BGP The Phase 1 decision function is invoked whenever the local BGP
speaker receives from a peer an UPDATE message that advertises a new speaker receives from a peer an UPDATE message that advertises a new
route, a replacement route, or withdrawn routes. route, a replacement route, or withdrawn routes.
The Phase 1 decision function is a separate process which completes The Phase 1 decision function is a separate process which completes
when it has no further work to do. when it has no further work to do.
The Phase 1 decision function shall lock an Adj-RIB-In prior to oper- The Phase 1 decision function locks an Adj-RIB-In prior to operating
ating on any route contained within it, and shall unlock it after on any route contained within it, and unlocks it after operating on
operating on all new or unfeasible routes contained within it. all new or unfeasible routes contained within it.
For each newly received or replacement feasible route, the local BGP For each newly received or replacement feasible route, the local BGP
speaker shall determine a degree of preference as follows: speaker determines a degree of preference as follows:
If the route is learned from an internal peer, either the value of If the route is learned from an internal peer, either the value of
the LOCAL_PREF attribute shall be taken as the degree of prefer- the LOCAL_PREF attribute is taken as the degree of preference, or
ence, or the local system may compute the degree of preference of the local system computes the degree of preference of the route
the route based on preconfigured policy information. Note that the based on preconfigured policy information. Note that the latter
latter (computing the degree of preference based on preconfigured (computing the degree of preference based on preconfigured policy
policy information) may result in formation of persistent routing information) may result in formation of persistent routing loops.
loops.
If the route is learned from an external peer, then the local BGP If the route is learned from an external peer, then the local BGP
speaker computes the degree of preference based on preconfigured speaker computes the degree of preference based on preconfigured
policy information. If the return value indicates that the route policy information. If the return value indicates that the route
is ineligible, the route may not serve as an input to the next is ineligible, the route MAY NOT serve as an input to the next
phase of route selection; otherwise the return value is used as phase of route selection; otherwise the return value is used as
the LOCAL_PREF value in any IBGP readvertisement. the LOCAL_PREF value in any IBGP readvertisement.
The exact nature of this policy information and the computation The exact nature of this policy information and the computation
involved is a local matter. involved is a local matter.
9.1.2 Phase 2: Route Selection 9.1.2 Phase 2: Route Selection
The Phase 2 decision function shall be invoked on completion of Phase The Phase 2 decision function is invoked on completion of Phase 1.
1. The Phase 2 function is a separate process which completes when it The Phase 2 function is a separate process which completes when it
has no further work to do. The Phase 2 process shall consider all has no further work to do. The Phase 2 process considers all routes
routes that are eligible in the Adj-RIBs-In. that are eligible in the Adj-RIBs-In.
The Phase 2 decision function shall be blocked from running while the The Phase 2 decision function is blocked from running while the Phase
Phase 3 decision function is in process. The Phase 2 function shall 3 decision function is in process. The Phase 2 function locks all
lock all Adj-RIBs-In prior to commencing its function, and shall Adj-RIBs-In prior to commencing its function, and unlocks them on
unlock them on completion. completion.
If the NEXT_HOP attribute of a BGP route depicts an address that is If the NEXT_HOP attribute of a BGP route depicts an address that is
not resolvable, or it would become unresolvable if the route was not resolvable, or it would become unresolvable if the route was
installed in the routing table the BGP route should be excluded from installed in the routing table the BGP route MUST be excluded from
the Phase 2 decision function. the Phase 2 decision function.
It is critical that routers within an AS do not make conflicting If the AS_PATH attribute of a BGP route contains an AS loop, the BGP
route should be excluded from the Phase 2 decision function. AS loop
detection is done by scanning the full AS path (as specified in the
AS_PATH attribute), and checking that the autonomous system number of
the local system does not appear in the AS path. Operations of a BGP
speaker that is configured to accept routes with its own autonomous
system number in the AS path are outside the scope of this document.
It is critical that BGP speakers within an AS do not make conflicting
decisions regarding route selection that would cause forwarding loops decisions regarding route selection that would cause forwarding loops
to occur. to occur.
For each set of destinations for which a feasible route exists in the For each set of destinations for which a feasible route exists in the
Adj-RIBs-In, the local BGP speaker shall identify the route that has: Adj-RIBs-In, the local BGP speaker identifies the route that has:
a) the highest degree of preference of any route to the same set a) the highest degree of preference of any route to the same set
of destinations, or of destinations, or
b) is the only route to that destination, or b) is the only route to that destination, or
c) is selected as a result of the Phase 2 tie breaking rules spec- c) is selected as a result of the Phase 2 tie breaking rules spec-
ified in 9.1.2.2. ified in 9.1.2.2.
The local speaker SHALL then install that route in the Loc-RIB, The local speaker SHALL then install that route in the Loc-RIB,
replacing any route to the same destination that is currently being replacing any route to the same destination that is currently being
held in the Loc-RIB. When the new BGP route is installed in the Rout- held in the Loc-RIB. When the new BGP route is installed in the Rout-
ing Table, care must be taken to ensure that existing routes to the ing Table, care must be taken to ensure that existing routes to the
same destination that are now considered invalid are removed from the same destination that are now considered invalid are removed from the
Routing Table. Whether or not the new BGP route replaces an existing Routing Table. Whether or not the new BGP route replaces an existing
non-BGP route in the Routing Table depends on the policy configured non-BGP route in the Routing Table depends on the policy configured
on the BGP speaker. on the BGP speaker.
The local speaker MUST determine the immediate next-hop address from The local speaker MUST determine the immediate next-hop address from
the NEXT_HOP attribute of the selected route (see section 5.1.3). If the NEXT_HOP attribute of the selected route (see Section 5.1.3). If
either the immediate next hop or the IGP cost to the NEXT_HOP (where either the immediate next hop or the IGP cost to the NEXT_HOP (where
the NEXT_HOP is resolved through an IGP route) changes, Phase 2: the NEXT_HOP is resolved through an IGP route) changes, Phase 2 Route
Route Selection should be performed again. Selection MUST be performed again.
Notice that even though BGP routes do not have to be installed in the Notice that even though BGP routes do not have to be installed in the
Routing Table with the immediate next hop(s), implementations must Routing Table with the immediate next hop(s), implementations MUST
take care that before any packets are forwarded along a BGP route, take care that before any packets are forwarded along a BGP route,
its associated NEXT_HOP address is resolved to the immediate its associated NEXT_HOP address is resolved to the immediate
(directly connected) next-hop address and this address (or multiple (directly connected) next-hop address and this address (or multiple
addresses) is finally used for actual packet forwarding. addresses) is finally used for actual packet forwarding.
Unresolvable routes SHALL be removed from the Loc-RIB and the routing Unresolvable routes SHALL be removed from the Loc-RIB and the routing
table. However, corresponding unresolvable routes SHOULD be kept in table. However, corresponding unresolvable routes SHOULD be kept in
the Adj-RIBs-In (in case they become resolvable). the Adj-RIBs-In (in case they become resolvable).
9.1.2.1 Route Resolvability Condition 9.1.2.1 Route Resolvability Condition
As indicated in Section 9.1.2, BGP routers should exclude unresolv- As indicated in Section 9.1.2, BGP speakers SHOULD exclude unresolv-
able routes from the Phase 2 decision. This ensures that only valid able routes from the Phase 2 decision. This ensures that only valid
routes are installed in Loc-RIB and the Routing Table. routes are installed in Loc-RIB and the Routing Table.
The route resolvability condition is defined as follows. The route resolvability condition is defined as follows.
1. A route Rte1, referencing only the intermediate network 1. A route Rte1, referencing only the intermediate network
address, is considered resolvable if the Routing Table contains at address, is considered resolvable if the Routing Table contains at
least one resolvable route Rte2 that matches Rte1's intermediate least one resolvable route Rte2 that matches Rte1's intermediate
network address and is not recursively resolved (directly or indi- network address and is not recursively resolved (directly or indi-
rectly) through Rte1. If multiple matching routes are available, rectly) through Rte1. If multiple matching routes are available,
only the longest matching route should be considered. only the longest matching route SHOULD be considered.
2. Routes referencing interfaces (with or without intermediate 2. Routes referencing interfaces (with or without intermediate
addresses) are considered resolvable if the state of the refer- addresses) are considered resolvable if the state of the refer-
enced interface is up and IP processing is enabled on this inter- enced interface is up and IP processing is enabled on this inter-
face. face.
BGP routes do not refer to interfaces, but can be resolved through BGP routes do not refer to interfaces, but can be resolved through
the routes in the Routing Table that can be of both types (those that the routes in the Routing Table that can be of both types (those that
specify interfaces or those that do not). IGP routes and routes to specify interfaces or those that do not). IGP routes and routes to
directly connected networks are expected to specify the outbound directly connected networks are expected to specify the outbound
interface. Static routes can specify the outbound interface, or the interface. Static routes can specify the outbound interface, or the
intermediate address, or both. intermediate address, or both.
Note that a BGP route is considered unresolvable not only in situa- Note that a BGP route is considered unresolvable not only in situa-
tions where the router's Routing Table contains no route matching the tions where the BGP speaker's Routing Table contains no route match-
BGP route's NEXT_HOP. Mutually recursive routes (routes resolving ing the BGP route's NEXT_HOP. Mutually recursive routes (routes
each other or themselves), also fail the resolvability check. resolving each other or themselves), also fail the resolvability
check.
It is also important that implementations do not consider feasible It is also important that implementations do not consider feasible
routes that would become unresolvable if they were installed in the routes that would become unresolvable if they were installed in the
Routing Table even if their NEXT_HOPs are resolvable using the cur- Routing Table even if their NEXT_HOPs are resolvable using the cur-
rent contents of the Routing Table (an example of such routes would rent contents of the Routing Table (an example of such routes would
be mutually recursive routes). This check ensures that a BGP speaker be mutually recursive routes). This check ensures that a BGP speaker
does not install in the Routing Table routes that will be removed and does not install in the Routing Table routes that will be removed and
not used by the speaker. Therefore, in addition to local Routing not used by the speaker. Therefore, in addition to local Routing
Table stability, this check also improves behavior of the protocol in Table stability, this check also improves behavior of the protocol in
the network. the network.
Whenever a BGP speaker identifies a route that fails the resolvabil- Whenever a BGP speaker identifies a route that fails the resolvabil-
ity check because of mutual recursion, an error message should be ity check because of mutual recursion, an error message SHOULD be
logged. logged.
9.1.2.2 Breaking Ties (Phase 2) 9.1.2.2 Breaking Ties (Phase 2)
In its Adj-RIBs-In a BGP speaker may have several routes to the same In its Adj-RIBs-In a BGP speaker may have several routes to the same
destination that have the same degree of preference. The local destination that have the same degree of preference. The local
speaker can select only one of these routes for inclusion in the speaker can select only one of these routes for inclusion in the
associated Loc-RIB. The local speaker considers all routes with the associated Loc-RIB. The local speaker considers all routes with the
same degrees of preference, both those received from internal peers, same degrees of preference, both those received from internal peers,
and those received from external peers. and those received from external peers.
The following tie-breaking procedure assumes that for each candidate The following tie-breaking procedure assumes that for each candidate
route all the BGP speakers within an autonomous system can ascertain route all the BGP speakers within an autonomous system can ascertain
the cost of a path (interior distance) to the address depicted by the the cost of a path (interior distance) to the address depicted by the
NEXT_HOP attribute of the route, and follow the same route selection NEXT_HOP attribute of the route, and follow the same route selection
algorithm. algorithm.
The tie-breaking algorithm begins by considering all equally prefer- The tie-breaking algorithm begins by considering all equally prefer-
able routes to the same destination, and then selects routes to be able routes to the same destination, and then selects routes to be
removed from consideration. The algorithm terminates as soon as only removed from consideration. The algorithm terminates as soon as only
one route remains in consideration. The criteria must be applied in one route remains in consideration. The criteria MUST be applied in
the order specified. the order specified.
Several of the criteria are described using pseudo-code. Note that Several of the criteria are described using pseudo-code. Note that
the pseudo-code shown was chosen for clarity, not efficiency. It is the pseudo-code shown was chosen for clarity, not efficiency. It is
not intended to specify any particular implementation. BGP implemen- not intended to specify any particular implementation. BGP implemen-
tations MAY use any algorithm which produces the same results as tations MAY use any algorithm which produces the same results as
those described here. those described here.
a) Remove from consideration all routes which are not tied for a) Remove from consideration all routes which are not tied for
having the smallest number of AS numbers present in their AS_PATH having the smallest number of AS numbers present in their AS_PATH
attributes. Note, that when counting this number, an AS_SET counts attributes. Note, that when counting this number, an AS_SET counts
as 1, no matter how many ASs are in the set. as 1, no matter how many ASs are in the set.
b) Remove from consideration all routes which are not tied for b) Remove from consideration all routes which are not tied for
having the lowest Origin number in their Origin attribute. having the lowest Origin number in their Origin attribute.
c) Remove from consideration routes with less-preferred c) Remove from consideration routes with less-preferred
MULTI_EXIT_DISC attributes. MULTI_EXIT_DISC is only comparable MULTI_EXIT_DISC attributes. MULTI_EXIT_DISC is only comparable
between routes learned from the same neighboring AS. Routes which between routes learned from the same neighboring AS (the neighbor-
do not have the MULTI_EXIT_DISC attribute are considered to have ing AS is determined from the AS_PATH attribute). Routes which do
the lowest possible MULTI_EXIT_DISC value. not have the MULTI_EXIT_DISC attribute are considered to have the
lowest possible MULTI_EXIT_DISC value.
This is also described in the following procedure: This is also described in the following procedure:
for m = all routes still under consideration for m = all routes still under consideration
for n = all routes still under consideration for n = all routes still under consideration
if (neighborAS(m) == neighborAS(n)) and (MED(n) < MED(m)) if (neighborAS(m) == neighborAS(n)) and (MED(n) < MED(m))
remove route m from consideration remove route m from consideration
In the pseudo-code above, MED(n) is a function which returns the In the pseudo-code above, MED(n) is a function which returns the
value of route n's MULTI_EXIT_DISC attribute. If route n has no value of route n's MULTI_EXIT_DISC attribute. If route n has no
skipping to change at page 64, line 8 skipping to change at page 68, line 47
ble MULTI_EXIT_DISC value, i.e. 0. ble MULTI_EXIT_DISC value, i.e. 0.
Similarly, neighborAS(n) is a function which returns the neighbor Similarly, neighborAS(n) is a function which returns the neighbor
AS from which the route was received. If the route is learned via AS from which the route was received. If the route is learned via
IBGP, and the other IBGP speaker didn't originate the route, it is IBGP, and the other IBGP speaker didn't originate the route, it is
the neighbor AS from which the other IBGP speaker learned the the neighbor AS from which the other IBGP speaker learned the
route. If the route is learned via IBGP, and the other IBGP route. If the route is learned via IBGP, and the other IBGP
speaker originated the route, it is the local AS. speaker originated the route, it is the local AS.
If a MULTI_EXIT_DISC attribute is removed before re-advertising a If a MULTI_EXIT_DISC attribute is removed before re-advertising a
route into IBGP, the MULTI_EXIT_DISC attribute may only be consid- route into IBGP, then comparison based on the received EBGP
ered in the comparison of EBGP learned routes, then removed, then MULTI_EXIT_DISC attribute MAY still be performed. If an implemen-
the remaining EBGP learned route may be compared to the remaining tation chooses to remove MULTI_EXIT_DISC, then the optional com-
IBGP learned routes, without considering the MULTI_EXIT_DISC parison on MULTI_EXIT_DISC if performed at all MUST be performed
attribute for those EBGP learned routes whose MULTI_EXIT_DISC will only among EBGP learned routes. The best EBGP learned route may
be dropped before advertising to IBGP. Including the then be compared with IBGP learned routes after the removal of the
MULTI_EXIT_DISC of an EBGP learned route in the comparison with an MULTI_EXIT_DISC attribute. If MULTI_EXIT_DISC is removed from a
IBGP learned route, then dropping the MULTI_EXIT_DISC and adver- subset of EBGP learned routes and the selected "best" EBGP learned
tising the route has been proven to cause route loops. route will not have MULTI_EXIT_DISC removed, then the
MULTI_EXIT_DISC must be used in the comparison with IBGP learned
routes. For IBGP learned routes the MULTI_EXIT_DISC MUST be used
in route comparisons which reach this step in the decision pro-
cess. Including the MULTI_EXIT_DISC of an EBGP learned route in
the comparison with an IBGP learned route, then removing the
MULTI_EXIT_DISC atribute and advertising the route has been proven
to cause route loops.
d) If at least one of the candidate routes was received from an d) If at least one of the candidate routes was received via EBGP,
external peer in a neighboring autonomous system, remove from con- remove from consideration all routes which were received via IBGP.
sideration all routes which were received from internal peers.
e) Remove from consideration any routes with less-preferred inte- e) Remove from consideration any routes with less-preferred inte-
rior cost. The interior cost of a route is determined by calcu- rior cost. The interior cost of a route is determined by calcu-
lating the metric to the NEXT_HOP for the route using the Routing lating the metric to the NEXT_HOP for the route using the Routing
Table. If the NEXT_HOP hop for a route is reachable, but no cost Table. If the NEXT_HOP hop for a route is reachable, but no cost
can be determined, then this step should be skipped (equivalently, can be determined, then this step should be skipped (equivalently,
consider all routes to have equal costs). consider all routes to have equal costs).
This is also described in the following procedure. This is also described in the following procedure.
for m = all routes still under consideration for m = all routes still under consideration
for n = all routes in still under consideration for n = all routes in still under consideration
if (cost(n) is better than cost(m)) if (cost(n) is lower than cost(m))
remove m from consideration remove m from consideration
In the pseudo-code above, cost(n) is a function which returns the In the pseudo-code above, cost(n) is a function which returns the
cost of the path (interior distance) to the address given in the cost of the path (interior distance) to the address given in the
NEXT_HOP attribute of the route. NEXT_HOP attribute of the route.
f) Remove from consideration all routes other than the route that f) Remove from consideration all routes other than the route that
was advertised by the BGP speaker whose BGP Identifier has the was advertised by the BGP speaker whose BGP Identifier has the
lowest value. lowest value.
g) Prefer the route received from the lowest neighbor address. g) Prefer the route received from the lowest peer address.
9.1.3 Phase 3: Route Dissemination 9.1.3 Phase 3: Route Dissemination
The Phase 3 decision function shall be invoked on completion of Phase The Phase 3 decision function is invoked on completion of Phase 2, or
2, or when any of the following events occur: when any of the following events occur:
a) when routes in the Loc-RIB to local destinations have changed a) when routes in the Loc-RIB to local destinations have changed
b) when locally generated routes learned by means outside of BGP b) when locally generated routes learned by means outside of BGP
have changed have changed
c) when a new BGP speaker - BGP speaker connection has been estab- c) when a new BGP speaker - BGP speaker connection has been estab-
lished lished
The Phase 3 function is a separate process which completes when it The Phase 3 function is a separate process which completes when it
has no further work to do. The Phase 3 Routing Decision function has no further work to do. The Phase 3 Routing Decision function is
shall be blocked from running while the Phase 2 decision function is blocked from running while the Phase 2 decision function is in pro-
in process. cess.
All routes in the Loc-RIB shall be processed into Adj-RIBs-Out All routes in the Loc-RIB are processed into Adj-RIBs-Out according
according to configured policy. This policy may exclude a route in to configured policy. This policy MAY exclude a route in the Loc-RIB
the Loc-RIB from being installed in a particular Adj-RIB-Out. A from being installed in a particular Adj-RIB-Out. A route SHALL NOT
route shall not be installed in the Adj-Rib-Out unless the destina- be installed in the Adj-Rib-Out unless the destination and NEXT_HOP
tion and NEXT_HOP described by this route may be forwarded appropri- described by this route may be forwarded appropriately by the Routing
ately by the Routing Table. If a route in Loc-RIB is excluded from a Table. If a route in Loc-RIB is excluded from a particular Adj-RIB-
particular Adj-RIB-Out the previously advertised route in that Adj- Out the previously advertised route in that Adj-RIB-Out MUST be with-
RIB-Out must be withdrawn from service by means of an UPDATE message drawn from service by means of an UPDATE message (see 9.2).
(see 9.2).
Route aggregation and information reduction techniques (see 9.2.2.1) Route aggregation and information reduction techniques (see 9.2.2.1)
may optionally be applied. may optionally be applied.
Any local policy which results in routes being added to an Adj-RIB- Any local policy which results in routes being added to an Adj-RIB-
Out without also being added to the local BGP speaker's forwarding Out without also being added to the local BGP speaker's forwarding
table, is outside the scope of this document. table, is outside the scope of this document.
When the updating of the Adj-RIBs-Out and the Routing Table is com- When the updating of the Adj-RIBs-Out and the Routing Table is com-
plete, the local BGP speaker shall run the Update-Send process of plete, the local BGP speaker runs the Update-Send process of 9.2.
9.2.
9.1.4 Overlapping Routes 9.1.4 Overlapping Routes
A BGP speaker may transmit routes with overlapping Network Layer A BGP speaker may transmit routes with overlapping Network Layer
Reachability Information (NLRI) to another BGP speaker. NLRI overlap Reachability Information (NLRI) to another BGP speaker. NLRI overlap
occurs when a set of destinations are identified in non-matching mul- occurs when a set of destinations are identified in non-matching mul-
tiple routes. Since BGP encodes NLRI using IP prefixes, overlap will tiple routes. Since BGP encodes NLRI using IP prefixes, overlap will
always exhibit subset relationships. A route describing a smaller always exhibit subset relationships. A route describing a smaller
set of destinations (a longer prefix) is said to be more specific set of destinations (a longer prefix) is said to be more specific
than a route describing a larger set of destinations (a shorter pre- than a route describing a larger set of destinations (a shorter pre-
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The precedence relationship effectively decomposes less specific The precedence relationship effectively decomposes less specific
routes into two parts: routes into two parts:
- a set of destinations described only by the less specific route, - a set of destinations described only by the less specific route,
and and
- a set of destinations described by the overlap of the less spe- - a set of destinations described by the overlap of the less spe-
cific and the more specific routes cific and the more specific routes
When overlapping routes are present in the same Adj-RIB-In, the more When overlapping routes are present in the same Adj-RIB-In, the more
specific route shall take precedence, in order from more specific to specific route takes precedence, in order from more specific to least
least specific. specific.
The set of destinations described by the overlap represents a portion The set of destinations described by the overlap represents a portion
of the less specific route that is feasible, but is not currently in of the less specific route that is feasible, but is not currently in
use. If a more specific route is later withdrawn, the set of desti- use. If a more specific route is later withdrawn, the set of desti-
nations described by the overlap will still be reachable using the nations described by the overlap will still be reachable using the
less specific route. less specific route.
If a BGP speaker receives overlapping routes, the Decision Process If a BGP speaker receives overlapping routes, the Decision Process
MUST consider both routes based on the configured acceptance policy. MUST consider both routes based on the configured acceptance policy.
If both a less and a more specific route are accepted, then the Deci- If both a less and a more specific route are accepted, then the Deci-
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attribute of the route. attribute of the route.
9.2 Update-Send Process 9.2 Update-Send Process
The Update-Send process is responsible for advertising UPDATE mes- The Update-Send process is responsible for advertising UPDATE mes-
sages to all peers. For example, it distributes the routes chosen by sages to all peers. For example, it distributes the routes chosen by
the Decision Process to other BGP speakers which may be located in the Decision Process to other BGP speakers which may be located in
either the same autonomous system or a neighboring autonomous system. either the same autonomous system or a neighboring autonomous system.
When a BGP speaker receives an UPDATE message from an internal peer, When a BGP speaker receives an UPDATE message from an internal peer,
the receiving BGP speaker shall not re-distribute the routing infor- the receiving BGP speaker SHALL NOT re-distribute the routing infor-
mation contained in that UPDATE message to other internal peers, mation contained in that UPDATE message to other internal peers,
unless the speaker acts as a BGP Route Reflector [RFC2796]. unless the speaker acts as a BGP Route Reflector [RFC2796].
As part of Phase 3 of the route selection process, the BGP speaker As part of Phase 3 of the route selection process, the BGP speaker
has updated its Adj-RIBs-Out. All newly installed routes and all has updated its Adj-RIBs-Out. All newly installed routes and all
newly unfeasible routes for which there is no replacement route shall newly unfeasible routes for which there is no replacement route SHALL
be advertised to its peers by means of an UPDATE message. be advertised to its peers by means of an UPDATE message.
A BGP speaker should not advertise a given feasible BGP route from A BGP speaker SHOULT NOT advertise a given feasible BGP route from
its Adj-RIB-Out if it would produce an UPDATE message containing the its Adj-RIB-Out if it would produce an UPDATE message containing the
same BGP route as was previously advertised. same BGP route as was previously advertised.
Any routes in the Loc-RIB marked as unfeasible shall be removed. Any routes in the Loc-RIB marked as unfeasible SHALL be removed.
Changes to the reachable destinations within its own autonomous sys- Changes to the reachable destinations within its own autonomous sys-
tem shall also be advertised in an UPDATE message. tem SHALL also be advertised in an UPDATE message.
If due to the limits on the maximum size of an UPDATE message (see If due to the limits on the maximum size of an UPDATE message (see
Section 4) a single route doesn't fit into the message, the BGP Section 4) a single route doesn't fit into the message, the BGP
speaker MUST not advertise the route to its peers and MAY choose to speaker MUST not advertise the route to its peers and MAY choose to
log an error locally. log an error locally.
9.2.1 Controlling Routing Traffic Overhead 9.2.1 Controlling Routing Traffic Overhead
The BGP protocol constrains the amount of routing traffic (that is, The BGP protocol constrains the amount of routing traffic (that is,
UPDATE messages) in order to limit both the link bandwidth needed to UPDATE messages) in order to limit both the link bandwidth needed to
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The parameter MinRouteAdvertisementInterval determines the minimum The parameter MinRouteAdvertisementInterval determines the minimum
amount of time that must elapse between advertisement and/or with- amount of time that must elapse between advertisement and/or with-
drawal of routes to a particular destination by a BGP speaker to a drawal of routes to a particular destination by a BGP speaker to a
peer. This rate limiting procedure applies on a per-destination peer. This rate limiting procedure applies on a per-destination
basis, although the value of MinRouteAdvertisementInterval is set on basis, although the value of MinRouteAdvertisementInterval is set on
a per BGP peer basis. a per BGP peer basis.
Two UPDATE messages sent by a BGP speaker to a peer that advertise Two UPDATE messages sent by a BGP speaker to a peer that advertise
feasible routes and/or withdrawal of unfeasible routes to some common feasible routes and/or withdrawal of unfeasible routes to some common
set of destinations MUST be separated by at least MinRouteAdvertise- set of destinations MUST be separated by at least
mentInterval. Clearly, this can only be achieved precisely by keeping MinRouteAdvertisementInterval. Clearly, this can only be achieved
a separate timer for each common set of destinations. This would be precisely by keeping a separate timer for each common set of destina-
unwarranted overhead. Any technique which ensures that the interval tions. This would be unwarranted overhead. Any technique which
between two UPDATE messages sent from a BGP speaker to a peer that ensures that the interval between two UPDATE messages sent from a BGP
advertise feasible routes and/or withdrawal of unfeasible routes to speaker to a peer that advertise feasible routes and/or withdrawal of
some common set of destinations will be at least MinRouteAdvertise- unfeasible routes to some common set of destinations will be at least
mentInterval, and will also ensure a constant upper bound on the MinRouteAdvertisementInterval, and will also ensure a constant upper
interval is acceptable. bound on the interval is acceptable.
Since fast convergence is needed within an autonomous system, either Since fast convergence is needed within an autonomous system, either
(a) the MinRouteAdvertisementInterval used for internal peers SHOULD (a) the MinRouteAdvertisementInterval used for internal peers SHOULD
be shorter than the MinRouteAdvertisementInterval used for external be shorter than the MinRouteAdvertisementInterval used for external
peers, or (b) the procedure describe in this section SHOULD NOT apply peers, or (b) the procedure describe in this section SHOULD NOT apply
for routes sent to internal peers. for routes sent to internal peers.
This procedure does not limit the rate of route selection, but only This procedure does not limit the rate of route selection, but only
the rate of route advertisement. If new routes are selected multiple the rate of route advertisement. If new routes are selected multiple
times while awaiting the expiration of MinRouteAdvertisementInterval, times while awaiting the expiration of MinRouteAdvertisementInterval,
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BGP speaker may avail itself of several methods to organize this BGP speaker may avail itself of several methods to organize this
information in an efficient manner. information in an efficient manner.
9.2.2.1 Information Reduction 9.2.2.1 Information Reduction
Information reduction may imply a reduction in granularity of policy Information reduction may imply a reduction in granularity of policy
control - after information is collapsed, the same policies will control - after information is collapsed, the same policies will
apply to all destinations and paths in the equivalence class. apply to all destinations and paths in the equivalence class.
The Decision Process may optionally reduce the amount of information The Decision Process may optionally reduce the amount of information
that it will place in the Adj-RIBs-Out by any of the following meth- that it will place in the Adj-RIBs-Out by any of the following
ods: methods:
a) Network Layer Reachability Information (NLRI): a) Network Layer Reachability Information (NLRI):
Destination IP addresses can be represented as IP address pre- Destination IP addresses can be represented as IP address pre-
fixes. In cases where there is a correspondence between the fixes. In cases where there is a correspondence between the
address structure and the systems under control of an autonomous address structure and the systems under control of an autonomous
system administrator, it will be possible to reduce the size of system administrator, it will be possible to reduce the size of
the NLRI carried in the UPDATE messages. the NLRI carried in the UPDATE messages.
b) AS_PATHs: b) AS_PATHs:
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Routes that have different MULTI_EXIT_DISC attribute SHALL NOT be Routes that have different MULTI_EXIT_DISC attribute SHALL NOT be
aggregated. aggregated.
Path attributes that have different type codes can not be aggregated Path attributes that have different type codes can not be aggregated
together. Path attributes of the same type code may be aggregated, together. Path attributes of the same type code may be aggregated,
according to the following rules: according to the following rules:
NEXT_HOP: NEXT_HOP:
When aggregating routes that have different NEXT_HOP attribute, When aggregating routes that have different NEXT_HOP attribute,
the NEXT_HOP attribute of the aggregated route SHALL identify the NEXT_HOP attribute of the aggregated route SHALL identify
an interface on the router that performs the aggregation. an interface on the BGP speaker that performs the aggregation.
ORIGIN attribute: ORIGIN attribute:
If at least one route among routes that are aggregated has ORI- If at least one route among routes that are aggregated has ORI-
GIN with the value INCOMPLETE, then the aggregated route must GIN with the value INCOMPLETE, then the aggregated route MUST
have the ORIGIN attribute with the value INCOMPLETE. Other- have the ORIGIN attribute with the value INCOMPLETE. Other-
wise, if at least one route among routes that are aggregated wise, if at least one route among routes that are aggregated
has ORIGIN with the value EGP, then the aggregated route must has ORIGIN with the value EGP, then the aggregated route MUST
have the origin attribute with the value EGP. In all other case have the origin attribute with the value EGP. In all other case
the value of the ORIGIN attribute of the aggregated route is the value of the ORIGIN attribute of the aggregated route is
IGP. IGP.
AS_PATH attribute: AS_PATH attribute:
If routes to be aggregated have identical AS_PATH attributes, If routes to be aggregated have identical AS_PATH attributes,
then the aggregated route has the same AS_PATH attribute as then the aggregated route has the same AS_PATH attribute as
each individual route. each individual route.
For the purpose of aggregating AS_PATH attributes we model each For the purpose of aggregating AS_PATH attributes we model each
AS within the AS_PATH attribute as a tuple <type, value>, where AS within the AS_PATH attribute as a tuple <type, value>, where
"type" identifies a type of the path segment the AS belongs to "type" identifies a type of the path segment the AS belongs to
(e.g. AS_SEQUENCE, AS_SET), and "value" is the AS number. If (e.g. AS_SEQUENCE, AS_SET), and "value" is the AS number. If
the routes to be aggregated have different AS_PATH attributes, the routes to be aggregated have different AS_PATH attributes,
then the aggregated AS_PATH attribute shall satisfy all of the then the aggregated AS_PATH attribute SHALL satisfy all of the
following conditions: following conditions:
- all tuples of type AS_SEQUENCE in the aggregated AS_PATH - all tuples of type AS_SEQUENCE in the aggregated AS_PATH
shall appear in all of the AS_PATH in the initial set of SHALL appear in all of the AS_PATH in the initial set of
routes to be aggregated. routes to be aggregated.
- all tuples of type AS_SET in the aggregated AS_PATH shall - all tuples of type AS_SET in the aggregated AS_PATH SHALL
appear in at least one of the AS_PATH in the initial set appear in at least one of the AS_PATH in the initial set
(they may appear as either AS_SET or AS_SEQUENCE types). (they may appear as either AS_SET or AS_SEQUENCE types).
- for any tuple X of type AS_SEQUENCE in the aggregated - for any tuple X of type AS_SEQUENCE in the aggregated
AS_PATH which precedes tuple Y in the aggregated AS_PATH, X AS_PATH which precedes tuple Y in the aggregated AS_PATH, X
precedes Y in each AS_PATH in the initial set which contains precedes Y in each AS_PATH in the initial set which contains
Y, regardless of the type of Y. Y, regardless of the type of Y.
- No tuple of type AS_SET with the same value shall appear - No tuple of type AS_SET with the same value SHALL appear
more than once in the aggregated AS_PATH. more than once in the aggregated AS_PATH.
- Multiple tuples of type AS_SEQUENCE with the same value - Multiple tuples of type AS_SEQUENCE with the same value
may appear in the aggregated AS_PATH only when adjacent to may appear in the aggregated AS_PATH only when adjacent to
another tuple of the same type and value. another tuple of the same type and value.
An implementation may choose any algorithm which conforms to An implementation may choose any algorithm which conforms to
these rules. At a minimum a conformant implementation shall be these rules. At a minimum a conformant implementation SHALL be
able to perform the following algorithm that meets all of the able to perform the following algorithm that meets all of the
above conditions: above conditions:
- determine the longest leading sequence of tuples (as - determine the longest leading sequence of tuples (as
defined above) common to all the AS_PATH attributes of the defined above) common to all the AS_PATH attributes of the
routes to be aggregated. Make this sequence the leading routes to be aggregated. Make this sequence the leading
sequence of the aggregated AS_PATH attribute. sequence of the aggregated AS_PATH attribute.
- set the type of the rest of the tuples from the AS_PATH - set the type of the rest of the tuples from the AS_PATH
attributes of the routes to be aggregated to AS_SET, and attributes of the routes to be aggregated to AS_SET, and
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- if the aggregated AS_PATH has more than one tuple with the - if the aggregated AS_PATH has more than one tuple with the
same value (regardless of tuple's type), eliminate all, but same value (regardless of tuple's type), eliminate all, but
one such tuple by deleting tuples of the type AS_SET from one such tuple by deleting tuples of the type AS_SET from
the aggregated AS_PATH attribute. the aggregated AS_PATH attribute.
- for each pair of adjacent tuples in the aggregated - for each pair of adjacent tuples in the aggregated
AS_PATH, if both tuples have the same type, merge them AS_PATH, if both tuples have the same type, merge them
together, as long as doing so will not cause a segment with together, as long as doing so will not cause a segment with
length greater than 255 to be generated. length greater than 255 to be generated.
Appendix F, section F.6 presents another algorithm that satis- Appendix F, Section F.6 presents another algorithm that satis-
fies the conditions and allows for more complex policy configu- fies the conditions and allows for more complex policy configu-
rations. rations.
ATOMIC_AGGREGATE: ATOMIC_AGGREGATE:
If at least one of the routes to be aggregated has If at least one of the routes to be aggregated has
ATOMIC_AGGREGATE path attribute, then the aggregated route ATOMIC_AGGREGATE path attribute, then the aggregated route
shall have this attribute as well. SHALL have this attribute as well.
AGGREGATOR: AGGREGATOR:
All AGGREGATOR attributes of all routes to be aggregated should Any AGGREGATOR attributes from the routes to be aggregated MUST
be ignored. The BGP speaker performing the route aggregation NOT be included in the aggregated route. The BGP speaker per-
may attach a new AGGREGATOR attribute (see Section 5.1.7). forming the route aggregation MAY attach a new AGGREGATOR
attribute (see Section 5.1.7).
9.3 Route Selection Criteria 9.3 Route Selection Criteria
Generally speaking, additional rules for comparing routes among sev- Generally speaking, additional rules for comparing routes among
eral alternatives are outside the scope of this document. There are several alternatives are outside the scope of this document. There
two exceptions: are two exceptions:
- If the local AS appears in the AS path of the new route being - If the local AS appears in the AS path of the new route being
considered, then that new route can not be viewed as better than considered, then that new route can not be viewed as better than
any other route (provided that the speaker is configured to accept any other route (provided that the speaker is configured to accept
such routes). If such a route were ever used, a routing loop could such routes). If such a route were ever used, a routing loop could
result (see Section 6.3). result.
- In order to achieve successful distributed operation, only - In order to achieve successful distributed operation, only
routes with a likelihood of stability can be chosen. Thus, an AS routes with a likelihood of stability can be chosen. Thus, an AS
must avoid using unstable routes, and it must not make rapid spon- SHOULD avoid using unstable routes, and it SHOULD NOT make rapid
taneous changes to its choice of route. Quantifying the terms spontaneous changes to its choice of route. Quantifying the terms
"unstable" and "rapid" in the previous sentence will require expe- "unstable" and "rapid" in the previous sentence will require expe-
rience, but the principle is clear. rience, but the principle is clear.
Care must be taken to ensure that BGP speakers in the same AS do not Care must be taken to ensure that BGP speakers in the same AS do not
make inconsistent decisions. make inconsistent decisions.
9.4 Originating BGP routes 9.4 Originating BGP routes
A BGP speaker may originate BGP routes by injecting routing informa- A BGP speaker may originate BGP routes by injecting routing informa-
tion acquired by some other means (e.g. via an IGP) into BGP. A BGP tion acquired by some other means (e.g. via an IGP) into BGP. A BGP
speaker that originates BGP routes shall assign the degree of prefer- speaker that originates BGP routes assigns the degree of preference
ence to these routes by passing them through the Decision Process to these routes by passing them through the Decision Process (see
(see Section 9.1). These routes may also be distributed to other BGP Section 9.1). These routes MAY also be distributed to other BGP
speakers within the local AS as part of the update process (see Sec- speakers within the local AS as part of the update process (see Sec-
tion 9.2). The decision whether to distribute non-BGP acquired routes tion 9.2). The decision whether to distribute non-BGP acquired routes
within an AS via BGP or not depends on the environment within the AS within an AS via BGP or not depends on the environment within the AS
(e.g. type of IGP) and should be controlled via configuration. (e.g. type of IGP) and SHOULD be controlled via configuration.
10 BGP Timers 10 BGP Timers
BGP employs five timers: ConnectRetry (see Section 8), Hold Time (see BGP employs five timers: ConnectRetry (see Section 8), Hold Time (see
Section 4.2), KeepAlive (see Section 8), MinASOriginationInterval Section 4.2), KeepAlive (see Section 8), MinASOriginationInterval
(see Section 9.2.1.2), and MinRouteAdvertisementInterval (see Section (see Section 9.2.1.2), and MinRouteAdvertisementInterval (see Section
9.2.1.1). 9.2.1.1).
The suggested default value for the ConnectRetry timer is 120 sec- The suggested default value for the ConnectRetry timer is 120 sec-
onds. onds.
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seconds. seconds.
The suggested default value for the MinRouteAdvertisementInterval is The suggested default value for the MinRouteAdvertisementInterval is
30 seconds. 30 seconds.
An implementation of BGP MUST allow the Hold Time timer to be config- An implementation of BGP MUST allow the Hold Time timer to be config-
urable on a per peer basis, and MAY allow the other timers to be con- urable on a per peer basis, and MAY allow the other timers to be con-
figurable. figurable.
To minimize the likelihood that the distribution of BGP messages by a To minimize the likelihood that the distribution of BGP messages by a
given BGP speaker will contain peaks, jitter should be applied to the given BGP speaker will contain peaks, jitter SHOULD be applied to the
timers associated with MinASOriginationInterval, KeepAlive, Min- timers associated with MinASOriginationInterval, KeepAlive, Min-
RouteAdvertisementInterval, and ConnectRetry. A given BGP speaker may RouteAdvertisementInterval, and ConnectRetry. A given BGP speaker MAY
apply the same jitter to each of these quantities regardless of the apply the same jitter to each of these quantities regardless of the
destinations to which the updates are being sent; that is, jitter destinations to which the updates are being sent; that is, jitter
need not be configured on a "per peer" basis. need not be configured on a "per peer" basis.
The suggested default amount of jitter shall be determined by multi- The suggested default amount of jitter SHALL be determined by multi-
plying the base value of the appropriate timer by a random factor plying the base value of the appropriate timer by a random factor
which is uniformly distributed in the range from 0.75 to 1.0. A new which is uniformly distributed in the range from 0.75 to 1.0. A new
random value should be picked each time the timer is set. The range random value SHOULD be picked each time the timer is set. The range
of the jitter random value MAY be configurable. of the jitter random value MAY be configurable.
Appendix A. Comparison with RFC1771 Appendix A. Comparison with RFC1771
There are numerous editorial changes (too many to list here). There are numerous editorial changes (too many to list here).
The following list the technical changes: The following list the technical changes:
Changes to reflect the usages of such features as TCP MD5 Changes to reflect the usages of such features as TCP MD5
[RFC2385], BGP Route Reflectors [RFC2796], BGP Confederations [RFC2385], BGP Route Reflectors [RFC2796], BGP Confederations
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Clarifications on the tie-breaking procedures. Clarifications on the tie-breaking procedures.
Clarifications on the frequency of route advertisements. Clarifications on the frequency of route advertisements.
Optional Parameter Type 1 (Authentication Information) has been Optional Parameter Type 1 (Authentication Information) has been
deprecated. deprecated.
UPDATE Message Error subcode 7 (AS Routing Loop) has been depre- UPDATE Message Error subcode 7 (AS Routing Loop) has been depre-
cated. cated.
OPEN Message Error subcode 5 (Authentication Failure) has been
deprecated.
Use of the Marker field for authentication has been deprecated. Use of the Marker field for authentication has been deprecated.
Use of TCP MD5 [RFC2385] for authentication is mandatory.
Appendix B. Comparison with RFC1267 Appendix B. Comparison with RFC1267
All the changes listed in Appendix A, plus the following. All the changes listed in Appendix A, plus the following.
BGP-4 is capable of operating in an environment where a set of reach- BGP-4 is capable of operating in an environment where a set of reach-
able destinations may be expressed via a single IP prefix. The con- able destinations may be expressed via a single IP prefix. The con-
cept of network classes, or subnetting is foreign to BGP-4. To cept of network classes, or subnetting is foreign to BGP-4. To
accommodate these capabilities BGP-4 changes semantics and encoding accommodate these capabilities BGP-4 changes semantics and encoding
associated with the AS_PATH attribute. New text has been added to associated with the AS_PATH attribute. New text has been added to
define semantics associated with IP prefixes. These abilities allow define semantics associated with IP prefixes. These abilities allow
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Appendix C. Comparison with RFC 1163 Appendix C. Comparison with RFC 1163
All of the changes listed in Appendices A and B, plus the following. All of the changes listed in Appendices A and B, plus the following.
To detect and recover from BGP connection collision, a new field (BGP To detect and recover from BGP connection collision, a new field (BGP
Identifier) has been added to the OPEN message. New text (Section Identifier) has been added to the OPEN message. New text (Section
6.8) has been added to specify the procedure for detecting and recov- 6.8) has been added to specify the procedure for detecting and recov-
ering from collision. ering from collision.
The new document no longer restricts the border router that is passed The new document no longer restricts the router that is passed in the
in the NEXT_HOP path attribute to be part of the same Autonomous Sys- NEXT_HOP path attribute to be part of the same Autonomous System as
tem as the BGP Speaker. the BGP Speaker.
New document optimizes and simplifies the exchange of the information New document optimizes and simplifies the exchange of the information
about previously reachable routes. about previously reachable routes.
Appendix D. Comparison with RFC 1105 Appendix D. Comparison with RFC 1105
All of the changes listed in Appendices A, B and C, plus the follow- All of the changes listed in Appendices A, B and C, plus the follow-
ing. ing.
Minor changes to the RFC1105 Finite State Machine were necessary to Minor changes to the RFC1105 Finite State Machine were necessary to
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support authentication. support authentication.
Note that quite often BGP, as specified in RFC 1105, is referred Note that quite often BGP, as specified in RFC 1105, is referred
to as BGP-1, BGP, as specified in RFC 1163, is referred to as to as BGP-1, BGP, as specified in RFC 1163, is referred to as
BGP-2, BGP, as specified in RFC1267 is referred to as BGP-3, and BGP-2, BGP, as specified in RFC1267 is referred to as BGP-3, and
BGP, as specified in this document is referred to as BGP-4. BGP, as specified in this document is referred to as BGP-4.
Appendix E. TCP options that may be used with BGP Appendix E. TCP options that may be used with BGP
If a local system TCP user interface supports TCP PUSH function, then If a local system TCP user interface supports TCP PUSH function, then
each BGP message should be transmitted with PUSH flag set. Setting each BGP message SHOULD be transmitted with PUSH flag set. Setting
PUSH flag forces BGP messages to be transmitted promptly to the PUSH flag forces BGP messages to be transmitted promptly to the
receiver. receiver.
If a local system TCP user interface supports setting precedence for If a local system TCP user interface supports setting of the DSCP
TCP connection, then TCP connection used by BGP should be opened with field [RFC2474] for TCP connections, then the TCP connection used by
precedence set to Internetwork Control (110) value (see also BGP SHOULD be opened with bits 0-2 of the DSCP field set to 110
[RFC791]). (binary).
A local system may protect its BGP connections by using the TCP MD5
Signature Option [RFC2385].
Appendix F. Implementation Recommendations Appendix F. Implementation Recommendations
This section presents some implementation recommendations. This section presents some implementation recommendations.
Appendix F.1 Multiple Networks Per Message Appendix F.1 Multiple Networks Per Message
The BGP protocol allows for multiple address prefixes with the same The BGP protocol allows for multiple address prefixes with the same
path attributes to be specified in one message. Making use of this path attributes to be specified in one message. Making use of this
capability is highly recommended. With one address prefix per message capability is highly recommended. With one address prefix per message
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the new message. When the entire routing table has been scanned, all the new message. When the entire routing table has been scanned, all
allocated messages are sent and their resources released. Maximum allocated messages are sent and their resources released. Maximum
compression is achieved when all the destinations covered by the compression is achieved when all the destinations covered by the
address prefixes share a common set of path attributes making it pos- address prefixes share a common set of path attributes making it pos-
sible to send many address prefixes in one 4096-byte message. sible to send many address prefixes in one 4096-byte message.
When peering with a BGP implementation that does not compress multi- When peering with a BGP implementation that does not compress multi-
ple address prefixes into one message, it may be necessary to take ple address prefixes into one message, it may be necessary to take
steps to reduce the overhead from the flood of data received when a steps to reduce the overhead from the flood of data received when a
peer is acquired or a significant network topology change occurs. One peer is acquired or a significant network topology change occurs. One
method of doing this is to limit the rate of updates. This will elim- method of doing this is to limit the rate of updates. This will
inate the redundant scanning of the routing table to provide flash eliminate the redundant scanning of the routing table to provide
updates for BGP peers and other routing protocols. A disadvantage of flash updates for BGP peers and other routing protocols. A disadvan-
this approach is that it increases the propagation latency of routing tage of this approach is that it increases the propagation latency of
information. By choosing a minimum flash update interval that is not routing information. By choosing a minimum flash update interval
much greater than the time it takes to process the multiple messages that is not much greater than the time it takes to process the multi-
this latency should be minimized. A better method would be to read ple messages this latency should be minimized. A better method would
all received messages before sending updates. be to read all received messages before sending updates.
Appendix F.2 Reducing route flapping Appendix F.2 Reducing route flapping
To avoid excessive route flapping a BGP speaker which needs to with- To avoid excessive route flapping a BGP speaker which needs to with-
draw a destination and send an update about a more specific or less draw a destination and send an update about a more specific or less
specific route SHOULD combine them into the same UPDATE message. specific route SHOULD combine them into the same UPDATE message.
Appendix F.3 Path attribute ordering Appendix F.3 Path attribute ordering
Implementations which combine update messages as described above in Implementations which combine update messages as described above in
skipping to change at page 79, line 14 skipping to change at page 84, line 12
segment; this segment is then placed in between the two consec- segment; this segment is then placed in between the two consec-
utive ASs identified in (a) of the aggregated attribute. utive ASs identified in (a) of the aggregated attribute.
c) For each pair of adjacent tuples in the aggregated AS_PATH, c) For each pair of adjacent tuples in the aggregated AS_PATH,
if both tuples have the same type, merge them together, as long if both tuples have the same type, merge them together, as long
as doing so will not cause a segment with length greater than as doing so will not cause a segment with length greater than
255 to be generated. 255 to be generated.
If as a result of the above procedure a given AS number appears If as a result of the above procedure a given AS number appears
more than once within the aggregated AS_PATH attribute, all, but more than once within the aggregated AS_PATH attribute, all, but
the last instance (rightmost occurrence) of that AS number should the last instance (rightmost occurrence) of that AS number SHOULD
be removed from the aggregated AS_PATH attribute. be removed from the aggregated AS_PATH attribute.
Security Considerations Security Considerations
BGP supports the ability to authenticate BGP messages by using BGP The authentication mechanism that an implementation of BGP MUST sup-
authentication. The authentication could be done on a per peer basis. port is specified in [RFC2385]. The authentication provided by this
In addition, BGP supports the ability to authenticate its data stream mechanism could be done on a per peer basis.
by using [RFC2385]. This authentication could be done on a per peer
basis. Finally, BGP could also use IPSec to authenticate its data
stream. Among the mechanisms mentioned in this paragraph, [RFC2385]
is the most widely deployed.
Normative References Security issues with BGP routing information dissemination are dis-
cussed in [XXX].
[RFC793] Postel, J., "Transmission Control Protocol - DARPA Internet IANA Considerations
Program Protocol Specification", RFC793, September 1981.
All extensions to this protocol, including new message types and Path
Attributes MUST only be made using the Standards Action process
defined in [RFC2434].
Normative References
[RFC791] Postel, J., "Internet Protocol - DARPA Internet Program Pro- [RFC791] Postel, J., "Internet Protocol - DARPA Internet Program Pro-
tocol Specification", RFC791, September 1981. tocol Specification", RFC791, September 1981.
[RFC793] Postel, J., "Transmission Control Protocol - DARPA Internet
Program Protocol Specification", RFC793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC2385, August 1998.
[RFC2434] Narten, T., Alvestrand, H., "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC2434, October 1998
[RFC2474] Nichols, K., et al.,"Definition of the Differentiated Ser-
vices Field (DS Field) in the IPv4 and IPv6 Headers", RFC2474, Decem-
ber 1998
Non-normative References Non-normative References
[RFC904] Mills, D., "Exterior Gateway Protocol Formal Specification", [RFC904] Mills, D., "Exterior Gateway Protocol Formal Specification",
RFC904, April 1984. RFC904, April 1984.
[RFC1092] Rekhter, Y., "EGP and Policy Based Routing in the New [RFC1092] Rekhter, Y., "EGP and Policy Based Routing in the New
NSFNET Backbone", RFC1092, February 1989. NSFNET Backbone", RFC1092, February 1989.
[RFC1093] Braun, H-W., "The NSFNET Routing Architecture", RFC1093, [RFC1093] Braun, H-W., "The NSFNET Routing Architecture", RFC1093,
February 1989. February 1989.
skipping to change at page 80, line 18 skipping to change at page 85, line 32
[RFC1518] Rekhter, Y., Li, T., "An Architecture for IP Address Allo- [RFC1518] Rekhter, Y., Li, T., "An Architecture for IP Address Allo-
cation with CIDR", RFC 1518, September 1993. cation with CIDR", RFC 1518, September 1993.
[RFC1519] Fuller, V., Li, T., Yu, J., and Varadhan, K., ""Classless [RFC1519] Fuller, V., Li, T., Yu, J., and Varadhan, K., ""Classless
Inter-Domain Routing (CIDR): an Address Assignment and Aggregation Inter-Domain Routing (CIDR): an Address Assignment and Aggregation
Strategy", RFC1519, September 1993. Strategy", RFC1519, September 1993.
[RFC1997] R. Chandra, P. Traina, T. Li, "BGP Communities Attribute", [RFC1997] R. Chandra, P. Traina, T. Li, "BGP Communities Attribute",
RFC 1997, August 1996. RFC 1997, August 1996.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC2385, August 1998.
[RFC2439] C. Villamizar, R. Chandra, R. Govindan, "BGP Route Flap [RFC2439] C. Villamizar, R. Chandra, R. Govindan, "BGP Route Flap
Damping", RFC2439, November 1998. Damping", RFC2439, November 1998.
[RFC2796] Bates, T., Chandra, R., Chen, E., "BGP Route Reflection - [RFC2796] Bates, T., Chandra, R., Chen, E., "BGP Route Reflection -
An Alternative to Full Mesh IBGP", RFC2796, April 2000. An Alternative to Full Mesh IBGP", RFC2796, April 2000.
[RFC2842] R. Chandra, J. Scudder, "Capabilities Advertisement with [RFC2842] R. Chandra, J. Scudder, "Capabilities Advertisement with
BGP-4", RFC2842. BGP-4", RFC2842.
[RFC2858] T. Bates, R. Chandra, D. Katz, Y. Rekhter, "Multiprotocol [RFC2858] T. Bates, R. Chandra, D. Katz, Y. Rekhter, "Multiprotocol
skipping to change at page 80, line 44 skipping to change at page 86, line 10
September 2000. September 2000.
[RFC3065] Traina, P, McPherson, D., Scudder, J., "Autonomous System [RFC3065] Traina, P, McPherson, D., Scudder, J., "Autonomous System
Confederations for BGP", RFC3065, February 2001. Confederations for BGP", RFC3065, February 2001.
[IS10747] "Information Processing Systems - Telecommunications and [IS10747] "Information Processing Systems - Telecommunications and
Information Exchange between Systems - Protocol for Exchange of Information Exchange between Systems - Protocol for Exchange of
Inter-domain Routeing Information among Intermediate Systems to Sup- Inter-domain Routeing Information among Intermediate Systems to Sup-
port Forwarding of ISO 8473 PDUs", ISO/IEC IS10747, 1993 port Forwarding of ISO 8473 PDUs", ISO/IEC IS10747, 1993
[XXX] Murphy, S., "BGP Security Vulnerabilities Analysis", draft-
ietf-idr-bgp-vuln-00.txt, work in progress
Editors' Addresses Editors' Addresses
Yakov Rekhter Yakov Rekhter
Juniper Networks Juniper Networks
email: yakov@juniper.net email: yakov@juniper.net
Tony Li Tony Li
Procket Networks, Inc. Procket Networks, Inc.
email: tli@procket.com email: tli@procket.com
Susan Hares Susan Hares
NextHop Technologies, Inc. NextHop Technologies, Inc.
email: skh@nexthop.com email: skh@nexthop.com
 End of changes. 

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