draft-ietf-idr-rfc3065bis-06.txt   rfc5065.txt 
INTERNET-DRAFT Paul Traina
Blissfully Retired Network Working Group P. Traina
Danny McPherson Request for Comments: 5065 Blissfully Retired
Arbor Networks Obsoletes: 3065 D. McPherson
John Scudder Category: Standards Track Arbor Networks
J. Scudder
Juniper Networks Juniper Networks
Expires: August 2007 February 2007 August 2007
Autonomous System Confederations for BGP Autonomous System Confederations for BGP
<draft-ietf-idr-rfc3065bis-06.txt>
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Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The Border Gateway Protocol (BGP) is an inter-autonomous system The Border Gateway Protocol (BGP) is an inter-autonomous system
routing protocol designed for Transmission Control Protocol/Internet routing protocol designed for Transmission Control Protocol/Internet
Protocol (TCP/IP) networks. BGP requires that all BGP speakers Protocol (TCP/IP) networks. BGP requires that all BGP speakers
within a single autonomous system (AS) must be fully meshed. This within a single autonomous system (AS) must be fully meshed. This
represents a serious scaling problem that has been well documented in represents a serious scaling problem that has been well documented in
a number of proposals. a number of proposals.
This document describes an extension to BGP which may be used to This document describes an extension to BGP that may be used to
create a confederation of autonomous systems that is represented as a create a confederation of autonomous systems that is represented as a
single autonomous system to BGP peers external to the confederation, single autonomous system to BGP peers external to the confederation,
thereby removing the "full mesh" requirement. The intention of this thereby removing the "full mesh" requirement. The intention of this
extension is to aid in policy administration and reduce the extension is to aid in policy administration and reduce the
management complexity of maintaining a large autonomous system. management complexity of maintaining a large autonomous system.
This document obsoletes RFC 3065.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction ....................................................3
1.1. Specification of Requirements . . . . . . . . . . . . . . . 4 1.1. Specification of Requirements ..............................3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Terminology ................................................3
2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Discussion ......................................................4
3. AS_CONFED Segment Type Extension . . . . . . . . . . . . . . . 6 3. AS_CONFED Segment Type Extension ................................5
4. Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Operation .......................................................5
4.1. AS_PATH Modification Rules. . . . . . . . . . . . . . . . . 7 4.1. AS_PATH Modification Rules .................................6
5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 8 5. Error Handling ..................................................8
5.1. Common Administrative Issues. . . . . . . . . . . . . . . . 9 5.1. Error Handling .............................................8
5.2. MED and LOCAL_PREF Handling . . . . . . . . . . . . . . . . 9 5.2. MED and LOCAL_PREF Handling ................................8
5.3. AS_PATH and Path Selection. . . . . . . . . . . . . . . . . 10 5.3. AS_PATH and Path Selection .................................9
6. Compatability Considerations . . . . . . . . . . . . . . . . . 10 6. Compatibility Considerations ...................................10
7. Deployment Considerations. . . . . . . . . . . . . . . . . . . 11 7. Deployment Considerations ......................................10
8. Security Considerations. . . . . . . . . . . . . . . . . . . . 11 8. Security Considerations ........................................10
9. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 12 9. Acknowledgments ................................................11
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. References ....................................................11
11. References. . . . . . . . . . . . . . . . . . . . . . . . . . 14 10.1. Normative References .....................................11
11.1. Normative References . . . . . . . . . . . . . . . . . . . 14 10.2. Informative References ...................................11
11.2. Informative References . . . . . . . . . . . . . . . . . . 14 Appendix A. Aggregate Routing Information .........................13
12. Appendix A: Aggregate Routing Information . . . . . . . . . . 15 Appendix B. Changes from RFC 3065 .................................13
13. Appendix B: Changes From RFC 3065 . . . . . . . . . . . . . . 15
14. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
As currently defined, BGP requires that all BGP speakers within a As originally defined, BGP requires that all BGP speakers within a
single AS must be fully meshed. The result is that for n BGP single AS must be fully meshed. The result is that for n BGP
speakers within an AS n*(n-1)/2 unique IBGP sessions are required. speakers within an AS, n*(n-1)/2 unique Internal BGP (IBGP) sessions
This "full mesh" requirement clearly does not scale when there are a are required. This "full mesh" requirement clearly does not scale
large number of IBGP speakers within the autonomous system, as is when there are a large number of IBGP speakers within the autonomous
common in many networks today. system, as is common in many networks today.
This scaling problem has been well documented and a number of This scaling problem has been well documented and a number of
proposals have been made to alleviate this [RFC 1863, RFC 2796]. proposals have been made to alleviate this, such as [RFC2796] and
This document presents another alternative alleviating the need for a [RFC1863] (made historic by [RFC4223]). This document presents
"full mesh" and is known as "Autonomous System Confederations for another alternative alleviating the need for a "full mesh" and is
BGP", or simply, "BGP Confederations". It has also been observed known as "Autonomous System Confederations for BGP", or simply, "BGP
that BGP Confederations may provide improvements in routing policy confederations". It has also been observed that BGP confederations
control. may provide improvements in routing policy control.
This document is a revision of [RFC 3065], which is itself a revision This document is a revision of, and obsoletes, [RFC3065], which is
to [RFC 1965]. It includes editorial changes, terminology itself a revision of [RFC1965]. It includes editorial changes,
clarifications and more explicit protocol specifications based on terminology clarifications, and more explicit protocol specifications
extensive implementation and deployment experience with BGP based on extensive implementation and deployment experience with BGP
Confederations. Confederations.
1.1. Specification of Requirements 1.1. 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 RFC 2119 [RFC 2119]. document are to be interpreted as described in RFC 2119 [RFC 2119].
1.2. Terminology 1.2. Terminology
AS Confederation AS Confederation
A collection of autonomous systems represented and advertised A collection of autonomous systems represented and advertised as a
as a single AS number to BGP speakers that are not members of single AS number to BGP speakers that are not members of the local
the local BGP confederation. BGP confederation.
AS Confederation Identifier AS Confederation Identifier
An externally visible autonomous system number that identifies An externally visible autonomous system number that identifies a
a BGP confederation as a whole. BGP confederation as a whole.
Member Autonomous System (Member-AS) Member Autonomous System (Member-AS)
An autonomous system that is contained in a given AS An autonomous system that is contained in a given AS
confederation. Note that "Member Autonomous System" and confederation. Note that "Member Autonomous System" and "Member-
"Member-AS" are used entirely interchangeably throughout AS" are used entirely interchangeably throughout this document.
this document.
Member-AS Number Member-AS Number
An autonomous system number identifier visible only within An autonomous system number identifier visible only within a BGP
a BGP confederation, and used to represent a Member-AS confederation, and used to represent a Member-AS within that
within that confederation. confederation.
2. Discussion 2. Discussion
It may be useful to subdivide autonomous systems with a very large It may be useful to subdivide autonomous systems with a very large
number of BGP speakers into smaller domains for purposes of number of BGP speakers into smaller domains for purposes of
controlling routing policy via information contained in the BGP controlling routing policy via information contained in the BGP
AS_PATH attribute. For example, one may choose to consider all BGP AS_PATH attribute. For example, one may choose to consider all BGP
speakers in a geographic region as a single entity. speakers in a geographic region as a single entity.
In addition to potential improvements in routing policy control, if In addition to potential improvements in routing policy control, if
techniques such as those presented here or in [RFC 2796] are not techniques such as those presented here or in [RFC4456] are not
employed, [BGP-4] requires BGP speakers in the same autonomous system employed, [BGP-4] requires BGP speakers in the same autonomous system
to establish a full mesh of TCP connections among all speakers for to establish a full mesh of TCP connections among all speakers for
the purpose of exchanging exterior routing information. In the purpose of exchanging exterior routing information. In
autonomous systems the number of intra-domain connections that need autonomous systems, the number of intra-domain connections that need
to be maintained by each border router can become significant. to be maintained by each border router can become significant.
Subdividing a large autonomous system allows a significant reduction Subdividing a large autonomous system allows a significant reduction
in the total number of intra-domain BGP connections, as the in the total number of intra-domain BGP connections, as the
connectivity requirements simplify to the model used for inter-domain connectivity requirements simplify to the model used for inter-domain
connections. connections.
Unfortunately, subdividing an autonomous system may increase the Unfortunately, subdividing an autonomous system may increase the
complexity of routing policy based on AS_PATH information for all complexity of routing policy based on AS_PATH information for all
members of the Internet. Additionally, this division increases the members of the Internet. Additionally, this division increases the
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single entity or autonomous system, when viewed from outside the single entity or autonomous system, when viewed from outside the
confines of the confederation of autonomous systems itself. confines of the confederation of autonomous systems itself.
3. AS_CONFED Segment Type Extension 3. AS_CONFED Segment Type Extension
Currently, BGP specifies that the AS_PATH attribute is a well-known Currently, BGP specifies that the AS_PATH attribute is a well-known
mandatory attribute that is composed of a sequence of AS path mandatory attribute that is composed of a sequence of AS path
segments. Each AS path segment is represented by a triple <path segments. Each AS path segment is represented by a triple <path
segment type, path segment length, path segment value>. segment type, path segment length, path segment value>.
In [BGP-4], the path segment type is a 1-octet long field with the In [BGP-4], the path segment type is a 1-octet field with the two
two following values defined: following values defined:
Value Segment Type Value Segment Type
1 AS_SET: unordered set of autonomous systems a route in 1 AS_SET: unordered set of autonomous systems that a route in
the UPDATE message has traversed the UPDATE message has traversed
2 AS_SEQUENCE: ordered set of autonomous systems a route 2 AS_SEQUENCE: ordered set of autonomous systems that a route
in the UPDATE message has traversed in the UPDATE message has traversed
This document specifies two additional segment types: This document specifies two additional segment types:
3 AS_CONFED_SEQUENCE: ordered set of Member Autonomous 3 AS_CONFED_SEQUENCE: ordered set of Member Autonomous
Systems in the local confederation that the UPDATE message Systems in the local confederation that the UPDATE message
has traversed has traversed
4 AS_CONFED_SET: unordered set of Member Autonomous Systems 4 AS_CONFED_SET: unordered set of Member Autonomous Systems
in the local confederation that the UPDATE message has in the local confederation that the UPDATE message has
traversed traversed
4. Operation 4. Operation
A member of a BGP confederation MUST use its AS Confederation A member of a BGP confederation MUST use its AS Confederation
Identifier in all transactions with peers that are not members of its Identifier in all transactions with peers that are not members of its
confederation. This AS confederation identifier is the "externally confederation. This AS Confederation Identifier is the "externally
visible" AS number and this number is used in OPEN messages and visible" AS number, and this number is used in OPEN messages and
advertised in the AS_PATH attribute. advertised in the AS_PATH attribute.
A member of a BGP confederation MUST use its Member-AS Number in all A member of a BGP confederation MUST use its Member-AS Number in all
transactions with peers that are members of the same confederation as transactions with peers that are members of the same confederation as
the local BGP speaker. the local BGP speaker.
A BGP speaker receiving an AS_PATH attribute containing an autonomous A BGP speaker receiving an AS_PATH attribute containing an autonomous
system matching its own AS Confederation Identifier SHALL treat the system matching its own AS Confederation Identifier SHALL treat the
path in the same fashion as if it had received a path containing its path in the same fashion as if it had received a path containing its
own AS number. own AS number.
A BGP speaker receiving an AS_PATH attribute containing an A BGP speaker receiving an AS_PATH attribute containing an
AS_CONFED_SEQUENCE or AS_CONFED_SET which contains its own Member-AS AS_CONFED_SEQUENCE or AS_CONFED_SET that contains its own Member-AS
Number SHALL treat the path in the same fashion as if it had received Number SHALL treat the path in the same fashion as if it had received
a path containing its own AS number. a path containing its own AS number.
4.1. AS_PATH Modification Rules 4.1. AS_PATH Modification Rules
When implementing BGP Confederations Section 5.1.2 of [BGP-4] is When implementing BGP confederations, Section 5.1.2 of [BGP-4] is
replaced with the following text: replaced with the following text:
When a BGP speaker propagates a route which it has learned from AS_PATH is a well-known mandatory attribute. This attribute
another BGP speaker's UPDATE message, it SHALL modify the route's identifies the autonomous systems through which routing information
AS_PATH attribute based on the location of the BGP speaker to which carried in this UPDATE message has passed. The components of this
the route will be sent: list can be AS_SETs, AS_SEQUENCEs, AS_CONFED_SETs or
AS_CONFED_SEQUENCES.
When a BGP speaker propagates a route it learned from another BGP
speaker's UPDATE message, it modifies the route's AS_PATH attribute
based on the location of the BGP speaker to which the route will be
sent:
a) When a given BGP speaker advertises the route to another BGP a) When a given BGP speaker advertises the route to another BGP
speaker located in its own Member-AS, the advertising speaker speaker located in its own Member-AS, the advertising speaker
SHALL NOT modify the AS_PATH attribute associated with the SHALL NOT modify the AS_PATH attribute associated with the route.
route.
b) When a given BGP speaker advertises the route to a BGP speaker b) When a given BGP speaker advertises the route to a BGP speaker
located in a neighboring autonomous system that is a member of located in a neighboring autonomous system that is a member of the
the local confederation, the advertising speaker SHALL update local confederation, the advertising speaker updates the AS_PATH
the AS_PATH attribute as follows: attribute 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_CONFED_SEQUENCE, the local system SHALL prepend its own AS_CONFED_SEQUENCE, the local system prepends its own Member-AS
Member-AS Number as the last element of the sequence (put number as the last element of the sequence (put it in the
it in the leftmost position). leftmost position with respect to the position of octets in the
protocol message). If the act of prepending will cause an
overflow in the AS_PATH segment (i.e., more than 255 ASs), it
SHOULD prepend a new segment of type AS_CONFED_SEQUENCE and
prepend its own AS number to this new segment.
2) if the first path segment of the AS_PATH is not of type 2) if the first path segment of the AS_PATH is not of type
AS_CONFED_SEQUENCE the local system SHALL prepend a new path AS_CONFED_SEQUENCE, the local system prepends a new path
segment of type AS_CONFED_SEQUENCE to the AS_PATH, including segment of type AS_CONFED_SEQUENCE to the AS_PATH, including
its own Member-AS Number in that segment. its own Member-AS Number in that segment.
3) if the AS_PATH is empty, the local system creates a path
segment of type AS_CONFED_SEQUENCE, places its own Member-AS
Number into that segment, and places that segment into the
AS_PATH.
c) When a given BGP speaker advertises the route to a BGP speaker c) When a given BGP speaker advertises the route to a BGP speaker
located in a neighboring autonomous system that is not a member of located in a neighboring autonomous system that is not a member of
the local confederation, the advertising speaker SHALL update the the local confederation, the advertising speaker SHALL update the
AS_PATH attribute as follows: AS_PATH attribute as follows:
1) if any path segments of the AS_PATH are of the type 1) if any path segments of the AS_PATH are of the type
AS_CONFED_SEQUENCE or AS_CONFED_SET, those segments MUST AS_CONFED_SEQUENCE or AS_CONFED_SET, those segments MUST be
be removed from the AS_PATH attribute, leaving the sanitized removed from the AS_PATH attribute, leaving the sanitized
AS_PATH attribute to be operated on by steps 2 or 3. AS_PATH attribute to be operated on by steps 2, 3 or 4.
2) if the first path segment of the remaining AS_PATH is of type 2) if the first path segment of the remaining AS_PATH is of type
AS_SEQUENCE, the local system SHALL prepend its own AS_SEQUENCE, the local system prepends its own AS Confederation
AS Confederation Identifier as the last element of the sequence Identifier as the last element of the sequence (put it in the
(put it in the leftmost position). leftmost position with respect to the position of octets in the
protocol message). If the act of prepending will cause an
overflow in the AS_PATH segment (i.e., more than 255 ASs), it
SHOULD prepend a new segment of type AS_SEQUENCE and prepend
its own AS number to this new segment.
3) if there are no path segments following the removal of the 3) if the first path segment of the remaining AS_PATH is of type
first AS_CONFED_SET/AS_CONFED_SEQUENCE segments, or if the AS_SET, the local system prepends a new path segment of type
first path segment of the remaining AS_PATH is not of type AS_SEQUENCE to the AS_PATH, including its own AS Confederation
AS_SEQUENCE the local system SHALL prepend a new path segment Identifier in that segment.
of type AS_SEQUENCE to the AS_PATH, including its own AS
Confederation Identifier in that segment.
When a BGP speaker originates a route: 4) if the remaining AS_PATH is empty, the local system creates a
path segment of type AS_SEQUENCE, places its own AS
Confederation Identifier into that segment, and places that
segment into the AS_PATH.
a) the originating speaker SHALL include an empty AS_PATH attribute When a BGP speaker originates a route then:
in all UPDATE messages sent to BGP speakers residing within the
same Member-AS. (An empty AS_PATH attribute is one whose length
field contains the value zero).
b) the originating speaker SHALL include its own Member-AS Number in a) the originating speaker includes its own AS Confederation
an AS_CONFED_SEQUENCE segment of the AS_PATH attribute of all Identifier in a path segment, of type AS_SEQUENCE, in the AS_PATH
UPDATE messages sent to BGP speakers located in neighboring attribute of all UPDATE messages sent to BGP speakers located in
neighboring autonomous systems that are not members of the local
confederation. In this case, the AS Confederation Identifier of
the originating speaker's autonomous system will be the only entry
the path segment, and this path segment will be the only segment
in the AS_PATH attribute.
b) the originating speaker includes its own Member-AS Number in a
path segment, of type AS_CONFED_SEQUENCE, in the AS_PATH attribute
of all UPDATE messages sent to BGP speakers located in neighboring
Member Autonomous Systems that are members of the local Member Autonomous Systems that are members of the local
confederation (i.e., the originating speaker's Member-AS Number confederation. In this case, the Member-AS Number of the
will be the only entry in the AS_PATH attribute). originating speaker's autonomous system will be the only entry the
path segment, and this path segment will be the only segment in
the AS_PATH attribute.
c) the originating speaker SHALL include its own AS Confederation c) the originating speaker includes an empty AS_PATH attribute in all
Identifier in an AS_SEQUENCE segment of the AS_PATH attribute of UPDATE messages sent to BGP speakers residing within the same
all UPDATE messages sent to BGP speakers located in neighboring Member-AS. (An empty AS_PATH attribute is one whose length field
autonomous systems that are not members of the local contains the value zero).
confederation. (In this case, the originating speaker's AS
Confederation Identifier will be the only entry in the AS_PATH Whenever the modification of the AS_PATH attribute calls for
attribute). including or prepending the AS Confederation Identifier or Member-AS
Number of the local system, the local system MAY include/prepend more
than one instance of that value in the AS_PATH attribute. This is
controlled via local configuration.
5. Error Handling 5. Error Handling
A BGP speaker MUST NOT transmit updates containing AS_CONFED_SET or A BGP speaker MUST NOT transmit updates containing AS_CONFED_SET or
AS_CONFED_SEQUENCE attributes to peers that are not members of the AS_CONFED_SEQUENCE attributes to peers that are not members of the
local confederation. local confederation.
It is an error for a BGP speaker to receive an update message with an It is an error for a BGP speaker to receive an UPDATE message with an
AS_PATH attribute which contains AS_CONFED_SEQUENCE or AS_CONFED_SET AS_PATH attribute that contains AS_CONFED_SEQUENCE or AS_CONFED_SET
segments from a neighbor which is not located in the same segments from a neighbor that is not located in the same
confederation. If a BGP speaker receives such an update message, it confederation. If a BGP speaker receives such an UPDATE message, it
SHALL treat the message as having a malformed AS_PATH according to SHALL treat the message as having a malformed AS_PATH according to
the procedures of [BGP-4] Section 6.3 ("UPDATE message error the procedures of [BGP-4], Section 6.3 ("UPDATE Message Error
handling"). Handling").
It is a error for a BGP speaker to receive an update message from a It is a error for a BGP speaker to receive an update message from a
confederation peer which is not in the same Member-AS that does not confederation peer that is not in the same Member-AS that does not
have AS_CONFED_SEQUENCE as the first segment. If a BGP speaker have AS_CONFED_SEQUENCE as the first segment. If a BGP speaker
receives such an update message, it SHALL treat the message as having receives such an UPDATE message, it SHALL treat the message as having
a malformed AS_PATH according to the procedures of [BGP-4] Section a malformed AS_PATH according to the procedures of [BGP-4], Section
6.3 ("Update message error handling"). 6.3 ("UPDATE Message Error Handling").
5.1. Common Administrative Issues 5.1. Common Administrative Issues
It is reasonable for Member Autonomous Systems of a confederation to It is reasonable for Member Autonomous Systems of a confederation to
share a common administration and IGP information for the entire share a common administration and Interior Gateway Protocol (IGP)
confederation. It is also reasonable for each Member-AS to run an information for the entire confederation. It is also reasonable for
independent IGP. In the latter case, the NEXT_HOP may need to be set each Member-AS to run an independent IGP. In the latter case, the
using policy (i.e., by default it is unchanged). NEXT_HOP may need to be set using policy (i.e., by default it is
unchanged).
5.2. MED and LOCAL_PREF Handling 5.2. MED and LOCAL_PREF Handling
It SHALL be legal for a BGP speaker to advertise an unchanged It SHALL be legal for a BGP speaker to advertise an unchanged
NEXT_HOP and MULTI_EXIT_DISC (MED) attribute to peers in a NEXT_HOP and MULTI_EXIT_DISC (MED) attribute to peers in a
neighboring Member-AS of the local confederation. neighboring Member-AS of the local confederation.
MEDs of two routes SHOULD only be compared if the first autonomous MEDs of two routes SHOULD only be compared if the first autonomous
systems in the first AS_SEQUENCE in both routes are the same - i.e., systems in the first AS_SEQUENCE in both routes are the same -- i.e.,
skip all the autonomous systems in the AS_CONFED_SET and skip all the autonomous systems in the AS_CONFED_SET and
AS_CONFED_SEQUENCE. An implementation MAY provide the ability to AS_CONFED_SEQUENCE. An implementation MAY provide the ability to
configure path selection such that MEDs of two routes are comparable configure path selection such that MEDs of two routes are comparable
if the first autonomous systems in the AS_PATHs are the same, if the first autonomous systems in the AS_PATHs are the same,
regardless of AS_SEQUENCE or AS_CONFED_SEQUENCE in the AS_PATH. regardless of AS_SEQUENCE or AS_CONFED_SEQUENCE in the AS_PATH.
An implementation MAY compare MEDs received from a Member-AS via An implementation MAY compare MEDs received from a Member-AS via
multiple paths. An implementation MAY compare MEDs from different multiple paths. An implementation MAY compare MEDs from different
Member Autonomous Systems of the same confederation. Member Autonomous Systems of the same confederation.
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5.3. AS_PATH and Path Selection 5.3. AS_PATH and Path Selection
Path selection criteria for information received from members inside Path selection criteria for information received from members inside
a confederation MUST follow the same rules used for information a confederation MUST follow the same rules used for information
received from members inside the same autonomous system, as specified received from members inside the same autonomous system, as specified
in [BGP-4]. in [BGP-4].
In addition, the following rules SHALL be applied: In addition, the following rules SHALL be applied:
1) If the AS_PATH is internal to the local confederation (i.e., there 1) If the AS_PATH is internal to the local confederation (i.e., there
are only AS_CONFED_* segments) consider the neighbor AS to be the are only AS_CONFED_* segments), consider the neighbor AS to be the
local AS. local AS.
2) Otherwise, if the first segment in the path which is not an 2) Otherwise, if the first segment in the path that is not an
AS_CONFED_SEQUENCE or AS_CONFED_SET is an AS_SEQUENCE, consider AS_CONFED_SEQUENCE or AS_CONFED_SET is an AS_SEQUENCE, consider
the neighbor AS to be the leftmost AS_SEQUENCE AS. the neighbor AS to be the leftmost AS_SEQUENCE AS.
3) When comparing routes using AS_PATH length, CONFED_SEQUENCE and 3) When comparing routes using AS_PATH length, CONFED_SEQUENCE and
CONFED_SETs SHOULD NOT be counted. CONFED_SETs SHOULD NOT be counted.
4) When comparing routes using the internal (iBGP learned) versus 4) When comparing routes using the internal (IBGP learned) versus
external (eBGP learned) rules, treat a route that is learned from external (EBGP learned) rules, treat a route that is learned from
a peer which is in the same confederation (not necessarily the a peer that is in the same confederation (not necessarily the same
same Member-AS) as "internal". Member-AS) as "internal".
6. Compatability Considerations 6. Compatibility Considerations
All BGP speakers participating as member of a confederation MUST All BGP speakers participating as members of a confederation MUST
recognize the AS_CONFED_SET and AS_CONFED_SEQUENCE segment type recognize the AS_CONFED_SET and AS_CONFED_SEQUENCE segment type
extensions to the AS_PATH attribute. extensions to the AS_PATH attribute.
Any BGP speaker not supporting these extensions will generate a Any BGP speaker not supporting these extensions will generate a
NOTIFICATION message specifying an "UPDATE Message Error" and a sub- NOTIFICATION message specifying an "UPDATE Message Error" and a sub-
code of "Malformed AS_PATH". code of "Malformed AS_PATH".
This compatibility issue implies that all BGP speakers participating This compatibility issue implies that all BGP speakers participating
in a confederation MUST support BGP confederations. However, BGP in a confederation MUST support BGP confederations. However, BGP
speakers outside the confederation need not support these extensions. speakers outside the confederation need not support these extensions.
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duplication of information will waste system resources, cause duplication of information will waste system resources, cause
unnecessary route flaps, and delay convergence. unnecessary route flaps, and delay convergence.
Care should be taken to manually filter duplicate advertisements Care should be taken to manually filter duplicate advertisements
caused by reachability information being relayed through multiple caused by reachability information being relayed through multiple
Member Autonomous Systems based upon the topology and redundancy Member Autonomous Systems based upon the topology and redundancy
requirements of the confederation. requirements of the confederation.
Additionally, confederations (as well as route reflectors), by Additionally, confederations (as well as route reflectors), by
excluding different reachability information from consideration at excluding different reachability information from consideration at
different locations in a confederation, have been shown [RFC 3365] to different locations in a confederation, have been shown [RFC3345] to
cause permanent oscillation between candidate routes when using the cause permanent oscillation between candidate routes when using the
tie breaking rules required by BGP [BGP-4]. Care must be taken when tie-breaking rules required by BGP [BGP-4]. Care must be taken when
selecting MED values and tie breaking policy to avoid these selecting MED values and tie-breaking policy to avoid these
situations. situations.
One potential way to avoid this is by configuring inter-Member-AS IGP One potential way to avoid this is by configuring inter-Member-AS IGP
metrics higher than intra-Member-AS IGP metrics and/or using other metrics higher than intra-Member-AS IGP metrics and/or using other
tie breaking policies to avoid BGP route selection based on tie-breaking policies to avoid BGP route selection based on
incomparable MEDs. incomparable MEDs.
8. Security Considerations 8. Security Considerations
This extension to BGP does not change the underlying security issues This extension to BGP does not change the underlying security issues
inherent in the existing BGP protocol, such as those described in inherent in the existing BGP protocol, such as those described in
[RFC 2385] and [BGP-VULN]. [RFC 2385] and [BGP-VULN].
9. Acknowledgments 9. Acknowledgments
The general concept of BGP confederations was taken from IDRP's The general concept of BGP confederations was taken from IDRP's
Routing Domain Confederations [ISO 10747]. Some of the introductory Routing Domain Confederations [ISO 10747]. Some of the introductory
text in this document was taken from [RFC 2796]. text in this document was taken from [RFC 2796].
The authors would like to acknowledge Jeffrey Haas for his extensive The authors would like to acknowledge Jeffrey Haas for his extensive
feedback on this document. We'd also like to thank Bruce Cole, feedback on this document. We'd also like to thank Bruce Cole,
Srihari Ramachandra, Alex Zinin, Naresh Kumar Paliwal, Jeffrey Haas, Srihari Ramachandra, Alex Zinin, Naresh Kumar Paliwal, Jeffrey Haas,
Cengiz Alaettinoglu, Mike Hollyman and Bruno Rijsman for their Cengiz Alaettinoglu, Mike Hollyman, and Bruno Rijsman for their
feedback and suggestions. feedback and suggestions.
Finally, we'd like to acknowledge Ravi Chandra and Yakov Rekhter for Finally, we'd like to acknowledge Ravi Chandra and Yakov Rekhter for
providing constructive and valuable feedback on earlier versions of providing constructive and valuable feedback on earlier versions of
this specification. this specification.
10. IANA Considerations 10. References
This spefication introduces no new IANA considerations and therefore
requires no actions on the part of IANA.
11. References
11.1. Normative References 10.1. Normative References
[BGP-4] Rekhter, Y., Li, T., and Hares, S., "A Border Gateway [BGP-4] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Protocol 4", RFC 4271. Border Gateway Protocol 4 (BGP-4)", RFC 4271, January
2006.
[RFC 1965] Traina, P. "Autonomous System Confederations for BGP", [RFC1965] Traina, P., "Autonomous System Confederations for BGP",
RFC 1965, June 1996. RFC 1965, June 1996.
[RFC 3065] Traina, P., McPherson, D. and Scudder, J., "Autonomous [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 3065, February 2001. System Confederations for BGP", RFC 3065, February 2001.
11.2. Informative References 10.2. Informative References
[ISO 10747] Kunzinger, C., Editor, "Inter-Domain Routing Protocol", [ISO 10747] Kunzinger, C., Editor, "Inter-Domain Routing Protocol",
ISO/IEC 10747, October 1993. ISO/IEC 10747, October 1993.
[RFC 1863] Haskin, D., "A BGP/IDRP Route Server alternative to a [RFC1863] Haskin, D., "A BGP/IDRP Route Server alternative to a full
full mesh routing", RFC 1863, October 1995. mesh routing", RFC 1863, October 1995.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Requirement Levels", RFC 2119, March 1997. Signature Option", RFC 2385, August 1998.
[RFC 2385] Heffernan, A., "Protection of BGP Sessions via the TCP [RFC3345] McPherson, D., Gill, V., Walton, D., and A. Retana,
MD5 Signature Option", RFC 2385, August 1998. "Border Gateway Protocol (BGP) Persistent Route
Oscillation Condition", RFC 3345, August 2002.
[RFC 2796] Bates, T., Chandra, R. and E. Chen, "BGP Route Reflection [RFC4223] Savola, P., "Reclassification of RFC 1863 to Historic",
An Alternative to Full Mesh IBGP", RFC 2796, April 2000. RFC 4223, October 2005.
[RFC 3365] McPherson, D., Gill, V., Walton, D., Retana, A., "Border [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC
Gateway Protocol (BGP) Persistent Route Oscillation Condition", 4272, January 2006.
RFC 3345, August 2002.
[BGP-VULN] Murphy, S., "BGP Security Vulnerabilities Analysis", [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Internet-Draft, "Work in Progress". Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, April 2006.
12. Appendix A: Aggregate Routing Information Appendix A. Aggregate Routing Information
As a practical matter, aggregation as discussed in [BGP-4] section As a practical matter, aggregation as discussed in [BGP-4], Section
9.2.2.2 is not generally employed within confederations. However, in 9.2.2.2, is not generally employed within confederations. However,
the event that such aggregation is performed within a confederation, in the event that such aggregation is performed within a
the rules of [BGP-4] should be followed, making the necessary confederation, the rules of [BGP-4] should be followed, making the
substitutions between AS_SET and AS_CONFED_SET and similarly, necessary substitutions between AS_SET and AS_CONFED_SET and
AS_SEQUENCE and AS_CONFED_SEQUENCE. Confederation-type segments similarly, AS_SEQUENCE and AS_CONFED_SEQUENCE. Confederation-type
(AS_CONFED_SET and AS_CONFED_SEQUENCE) MUST be kept separate from segments (AS_CONFED_SET and AS_CONFED_SEQUENCE) MUST be kept separate
non-confederation segments (AS_SET and AS_SEQUENCE). An from non-confederation segments (AS_SET and AS_SEQUENCE). An
implementation could also choose to provide a form of aggregation implementation could also choose to provide a form of aggregation
wherein non-confederation segments are aggregated as discussed in wherein non-confederation segments are aggregated as discussed in
[BGP-4] section 9.2.2.2 and confederation-type segments are not [BGP-4], Section 9.2.2.2, and confederation-type segments are not
aggregated. aggregated.
Support for aggregation of confederation-type segments is not Support for aggregation of confederation-type segments is not
mandatory. mandatory.
13. Appendix B: Changes From RFC 3065 Appendix B. Changes from RFC 3065
The primary trigger for an update to RFC 3065 was regarding issues The primary trigger for an update to RFC 3065 was regarding issues
associated with AS path segment handling, in particular what to do associated with AS path segment handling, in particular what to do
when interacting with BGP peers external to a confederation and to when interacting with BGP peers external to a confederation and to
ensure AS_CONFED_[SET|SEQUENCE] segment types are not propagated to ensure AS_CONFED_[SET|SEQUENCE] segment types are not propagated to
peers outside of a confederation. peers outside of a confederation.
As such, the "Error Handling" section above was added and applies not As such, the "Error Handling" section above was added and applies not
only to explicitly call attention to BGP Confederation speakers, but only to BGP confederation speakers, but to all BGP speakers.
to all BGP speakers.
Other changes are mostly trivial and surrounding some clarification Other changes are mostly trivial and surrounding some clarification
and consistency in terminology and denoting that and consistency in terminology and denoting that
AS_CONFED_[SET|SEQUENCE] Segment Type handling should be just as it AS_CONFED_[SET|SEQUENCE] Segment Type handling should be just as it
is in the base BGP specification [BGP-4]. is in the base BGP specification [BGP-4].
14. Authors' Addresses Authors' Addresses
Paul Traina Paul Traina
Blissfully Retired Blissfully Retired
Email: bgp-confederations <possibly at> st04.pst.org Email: bgp-confederations@st04.pst.org
Danny McPherson Danny McPherson
Arbor Networks Arbor Networks
EMail: danny@arbor.net EMail: danny@arbor.net
John G. Scudder John G. Scudder
Juniper Networks Juniper Networks
EMail: jgs@juniper.net EMail: jgs@juniper.net
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contained in BCP 78, and except as set forth therein, the authors
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skipping to change at page 16, line 40 skipping to change at page 14, line 45
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Copyright Statement Acknowledgement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST
AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT
THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR
PURPOSE.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF Funding for the RFC Editor function is currently provided by the
Administrative Support Activity (IASA). Internet Society.
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