draft-ietf-ospf-ara-01.txt   draft-ietf-ospf-ara-02.txt 
Expiration Date: May 1998 Expiration Date: May 1998
File name: draft-ietf-ospf-ara-01.txt File name: draft-ietf-ospf-ara-02.txt
The OSPF Address Resolution Advertisement Option The OSPF Address Resolution Advertisement Option
Rob Coltun Rob Coltun
FORE Systems FORE Systems
(301) 571-2521 (703) 245-4543
rcoltun@fore.com rcoltun@fore.com
Juha Heinanen Juha Heinanen
Telecom Finland Telia Finland, Inc.
+358 400 500 958 +358 303 944 808
jh@tele.fi jh@telia.fi
Status Of This Memo Status Of This Memo
This document is an Internet-Draft. Internet-Drafts are working docu- This document is an Internet-Draft. Internet-Drafts are working docu-
ments of the Internet Engineering Task Force (IETF), its areas, and ments of the Internet Engineering Task Force (IETF), its areas, and
its working groups. Note that other groups may also distribute work- its working groups. Note that other groups may also distribute work-
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Coltun, Heinanen [Page 1]
Table Of Contents Table Of Contents
1.0 Abstract ................................................. 4 1.0 Abstract ................................................. 4
2.0 Overview ................................................. 4 2.0 Overview ................................................. 4
2.1 Address Resolution Advertisements ........................ 5 2.1 Acknowledgments .......................................... 5
2.2 ARA Association Table .................................... 5 3.0 Examples ................................................. 6
2.3 Logical Network ID List .................................. 5 3.1 Example 1: Intra-Area .................................... 6
2.4 Routing Table Extensions ................................. 5 3.2 Example 2: Inter-Area .................................... 7
2.5 Restricting Shortcut Connectivity ........................ 6 3.3 Example 3: Multiple Logical Networks ..................... 8
2.6 Acknowledgments .......................................... 6 4.0 A Brief Comparison Of Address Resolution Models .......... 9
3.0 A Brief Comparison Of Address Resolution Models .......... 7 5.0 ARA Components ........................................... 11
4.0 ARA Associations ......................................... 8 5.1 Address Resolution Advertisements ........................ 11
5.0 Examples ................................................. 9 5.2 ARA Association Table .................................... 11
5.1 Example 1: Intra-Area .................................... 9 5.3 Logical Network ID List .................................. 12
5.2 Example 2: Inter-Area .................................... 10 5.4 Routing Table Extensions ................................. 12
5.3 Example 3: Multiple Logical Networks ..................... 11 5.5 Restricting Shortcut Connectivity ........................ 12
6.0 Description Of ARA Packet Formats ........................ 12 6.0 ARA Associations ......................................... 13
6.1 Vertex Types And Vertex Identifiers ...................... 13 7.0 Description Of ARA Packet Formats ........................ 14
7.0 Distribution Of ARA Information .......................... 14 7.1 Vertex Types And Vertex Identifiers ...................... 14
7.1 Originating Inter-Area ARAs .............................. 15 8.0 Distribution Of ARA Information .......................... 15
8.0 ARA Routing Table Extensions ............................. 17 8.1 Originating Inter-Area ARAs .............................. 17
8.1 Adding ARA Routing Table Extensions ...................... 18 9.0 ARA Routing Table Extensions ............................. 19
8.1.1 Modifications To The Intra-Area Route Calculation ...... 18 9.1 Adding ARA Routing Table Extensions ...................... 20
8.1.2 Modifications To The Inter-Area Route Calculation ...... 19 9.1.1 Modifications To The Intra-Area Route Calculation ...... 20
8.1.3 Modifications To The AS External Route Calculation ..... 20 9.1.2 Modifications To The Inter-Area Route Calculation ...... 21
9.1.3 Modifications To The AS External Route Calculation ..... 22
Coltun, Heinanen [Page 2] 9.2 Routing Table Extension Completion ....................... 23
9.0 Receiving ARAs ........................................... 21
10.0 Additional Data Structures And APIs ..................... 21 10.0 Receiving ARAs .......................................... 24
Appendix A: ARA Packet Formats ............................... 23 11.0 Additional Data Structures And APIs ..................... 24
A.1 The ARA Header ........................................... 23 12.0 Security Considerations ................................. 24
A.2 Intra-Area Router ARA .................................... 26 Appendix A: ARA Packet Formats ............................... 27
A.3 Intra-Area Network ARA ................................... 27 A.1 The ARA Header ........................................... 27
A.4 Inter-Area Router ARA .................................... 28 A.2 Intra-Area Router ARA .................................... 30
A.5 Inter-Area Network ARA ................................... 30 A.3 Intra-Area Network ARA ................................... 31
A.6 Vertex Association ....................................... 31 A.4 Inter-Area Router ARA .................................... 32
A.7 Resolution Information ................................... 32 A.5 Inter-Area Network ARA ................................... 34
A.7.1 ATM Address ............................................ 34 A.6 Vertex Association ....................................... 35
A.7.2 ATM LIJ Call Identification ............................ 35 A.7 Resolution Information ................................... 37
References ................................................... 35 A.7.1 ATM Address ............................................ 38
Coltun, Heinanen [Page 3] A.7.2 ATM LIJ Call Identification ............................ 39
References ................................................... 40
1.0 Abstract 1.0 Abstract
This document defines an OSPF option to enable routers to distribute This document defines an optional extension to OSPF which enables
IP to link-layer address resolution information. An OSPF Address routers to distribute IP to link-layer address resolution information
Resolution Advertisement (ARA) may include media-specific information An OSPF Address Resolution Advertisement (ARA) may include media-
such as a multipoint-to-point connection identifier along with the specific information such as a multipoint-to-point connection identifier
address resolution information to support media-specific functions. along with the address resolution information to support media-specific
The ARA option can be used to support router-to-router inter-subnet functions. The ARA option can be used to support router-to-router
shortcut architectures such as those described in [HEIN]. inter-subnet shortcut architectures such as those described in [HEIN].
2.0 Overview 2.0 Overview
Along with the evolution of switched layer 2 technologies comes the Along with the evolution of switched layer 2 technologies comes the
ability to provide inter-subnet shortcut data switching (bypassing ability to provide inter-subnet shortcut data switching (bypassing
router intervention). Before the ingress devices is able to dynami- layer-3 forwarding intervention). Before the ingress devices is able
cally set up the switched path it must have the link-layer address of to dynamically set up the switched path it must have the link-layer
the egress device. Acquisition of the egress device's link-layer address of the egress device. Acquisition of the egress device's
address may be through configuration or through a dynamic mechanism link-layer address may be through configuration or through a dynamic
which resolves an IP address (or an IP end-point identifier) to a mechanism which resolves an IP address (or an IP end-point identifier)
link-layer address. to a link-layer address.
This document introduces a method for IP to link-layer address resolu- This document introduces a method for IP to link-layer addresses reso-
tion to support router-to-router and router-to-network inter-subnet lution which supports router-to-router and router-to-network inter-
shortcuts. The ARA option supports both topology-derived and data- subnet shortcuts. Fundamentally, the option provides a mechanism for
driven shortcuts architectures with simple extensions to OSPF. Dis- routers to distribute their IP to link-layer address resolution infor-
tribution of address resolution information is performed using stan- mation (referred to in this document as link-layer associations), and
dard OSPF flooding mechanisms. This document does not define an for routers to determine the link-layer association which are closest
architecture but is meant to be used with architectures such as those to their target networks (within an OSPF domain). Address Resolution
defined in [HEIN]. The ARA option is designed to support the follow- Advertisements (ARAs) are used to distribute the link-layer associa-
ing operations. tions of routers (Router ARAs) and their directly connected networks
(Network ARAs) within and between OSPF areas. Distribution of ARAs is
performed using standard OSPF flooding mechanisms. ARA information is
encapsulated in Opaque LSAs [OPAQ] and flooded using the mechanisms
defined in [OPAQ].
The ARA option supports both topology-derived and data-driven shortcut
architectures with this simple extensions to OSPF. This document does
not define an architecture but is meant to be used with architectures
such as those defined in [HEIN]. The ARA option is designed to sup-
port the following types of operations.
Shortcuts between core or access routers within ISP Backbones. Shortcuts between core or access routers within ISP Backbones.
Shortcuts in enterprise networks between routers in the same OSPF Shortcuts in enterprise networks between routers in the same OSPF
autonomous system, between OSPF internal routers and autonomous autonomous system, between OSPF internal routers and autonomous
system border routers (ASBR) or between routers and servers. system border routers (ASBR) or between routers and servers.
Distributed router architectures. Distributed router architectures.
Interoperation with ION NHRP and ATMF MPOA. Interoperation with ION NHRP and ATMF MPOA.
Inter-subnet multicast shortcuts using LIJ or Point-to-MultiPoint Inter-subnet multicast shortcuts using LIJ or Point-to-MultiPoint
procedures. procedures.
Coltun, Heinanen [Page 4] 2.1 Acknowledgments
2.1 Address Resolution Advertisements The authors would like to thank Atul Bansal, Lou Berger, Yiqun Cai,
John Moy, Stephen Shew, George Swallow and the rest of the OSPF
Working Group for the ideas and support they have given to this project.
The ARA option defines a set of link-state advertisements called 3.0 Examples
address resolution advertisements (ARAs). ARAs are used to distribute
link-layer information of routers and their directly connected net-
works within and between OSPF areas. ARA information is encapsulated
in Opaque LSAs (see [OPAQ] for a further description of Opaque LSAs).
Three LS Types (LS Type 9, 10 and 11) constitute the Opaque class of
link-state advertisements. Each of the three Opaque link-state types
have a scope associated with them so that distribution of the informa-
tion may be limited appropriately by the originator of the LSA.
Because the flooding scope for ARAs is always area local, ARAs are
encapsulated in LS Type 10 LSAs. Opaque LSAs have a sub-type which
identifies the specific information that is carried within the LSA.
ARA uses Opaque-types 1, 2, 3 and 4. See section 6.0 for a further
description of the ARA packet formats.
2.2 ARA Association Table In this section three example ARA topologies are presented for the
purpose of explaining the ARA model and capabilities. These examples
include a single-area topology with intra-area shortcuts, a multiple-
area topology with inter-area shortcuts and an example of shortcuts
using the ARA multiple logical network capability.
A router implementing the ARA option maintains a table of link-layer 3.1 Example 1: Intra-Area
associations for each of its OSPF areas. The ARA Association Table is
used in calculating the ARA routing table extensions and by area
border routers in the inter-area ARA origination process. The indexes
for an entry in this table entry are the Vertex Type, Vertex ID and
the Vertex Originator. The Vertex Type identifies the type of IP
topology element that the link-layer information is being associated
with (i.e., a router or a network). The Vertex ID identifies a piece
of the OSPF topology (i.e., a router ID or an IP network number). The
Vertex Originator is the ARA originator's Router ID.
2.3 Logical Network ID List Consider the sample single-area topology in Figure 1 below. In this
example RT1, RT2 and RT5 support the ARA option (by definition they
also support the Opaque LSA option) and RT4 supports the Opaque LSA
option only (this is necessary so that RT4 redistributes the ARAs ori-
ginated by RT1, RT2 and RT5). RT2 and RT5 have each originated a
Router ARA (R-ARA) with an intra-area router association and RT5 has
originated a Network ARA (N-ARA) with an intra-area network associa-
tion for N5.
An ARA capable router maintains a configured list of logical networks As a result of running the routing table calculation, RT1 has entries
IDs. This list represents the logical networks that a router is con- for N1-N8 in its routing table. The entry for N2 references the
nected to and may be used to restrict the set of devices that the link-layer associations distributed in RT2's R-ARA, the entries for
router may setup shortcuts to (see section 2.5 "Restricting Shortcut N3, N4, N6, N7, N8 references the link-layer associations distributed
Connectivity"). The absence of entries in the router's list of Logi- in RT5's R-ARA and the entry for N5 references the link-layer associa-
cal Network IDs means that the router will only activate ARA Associa- tions distributed in RT5's intra-area N-ARA.
tion Table entries with the default Logical Network ID (Logical Net-
work ID 0).
2.4 Routing Table Extensions + ARA
| +---+ N3 N5 (ARA)
N1|--|RT1|\ \ N4 /
| +---+ \ \ | /
+ \ \|/
\+---+ +---+
|RT4|------------|RT5| ARA
+---+ +---+
+ ARA / | N7
| +---+ / | /
N2|--|RT2|/ | /
| +---+ +---+ +---+/
+ |RT3|-----------|RT6|----N8
+---+ +---+
|
|
+---------+
N6
Associations are added to the routing table during the OSPF routing Figure 1: Sample Single-Area Topology
table calculation (see section 8.1 entitled "Adding ARA Routing Table
Coltun, Heinanen [Page 5] 3.2 Example 2: Inter-Area
Extensions"). That is, in addition to the standard information fields
contained in the routing table (IP network number, IP mask, next-hop
interface, etc.), the routing table is extended to contain link-layer
associations. However, only 'active' link-layer associations are
added to the routing table. Associations containing a logical network
ID that matches a currently enabled entry in the router's list of log-
ical network IDs are considered to be active. Both active and non-
active link-layer associations may be included in inter-area ARAs that
are originated by an ABR.
The routing table (and its ARA routing table extensions) must be Consider the sample 2-area topology in Figure 2 below. In this exam-
recalculated if 1) there is a change to the OSPF topology, 2) there is ple RT1, RT2, RT3, RT4, RT6 and RT7 support the ARA option, and RT5
a change to the components in the ARA Association Table (see section supports the Opaque option. N4 is an AS external route (which is
9.0 "Receiving ARAs"), or 3) the router's logical network connectivity flooded to all areas) and RT6 is an ASBR. RT4 is an area-border
has changed (e.g., the logical network ID list is modified or the router and originates an LS Type-4 LSA on behalf of RT6 and a LS
status of the router's connections to one of its logical networks has Type-3 LSA for N5 into area 1.1.1.1.
changed).
The use of the routing table extensions are application specific and Within area 1.1.1.1, RT1, RT2, RT3 and RT4 originate intra-area R-
beyond the scope of this document. See [HEIN] for an example of an ARAs. Within the backbone RT6 and RT7 originate intra-area R-ARAs and
ARA user application. R7 originates a N-ARA for N5. All backbone ARAs of have their the P-
bit set (this bit informs ABRs that the ARA may be propagated between
areas). RT4 originates an inter-area R-ARA for RT6 (which is an ASBR)
as well as an inter-area N-ARA for N5 into area 1.1.1.1 RT4 does not
originate an inter-area R-ARA for RT7 because it is not an ASBR.
2.5 Restricting Shortcut Connectivity As a result of running the routing table calculation, RT1 has entries
for N1-N5 in its routing table. The entry for N2 references the
link-layer associations distributed in RT3's R-ARA, the entry for N3
references the link-layer associations distributed in RT4's intra-area
R-ARA, the entry for N4 references the link-layer associations distri-
buted in RT4's inter-area R-ARA (indirectly referencing RT6's R-ARA)
and the entry for N5 references the link-layer associations
distributed in RT4's inter-area N5 N-ARA.
As a result of setting up shortcuts in an OSPF topology between ARA- + ARA ARA |
capable routers, the shortcut connectivity may become fully meshed. | +---+ +---+ |
In many environments this may be desirable whereas in in others this N1|--|RT1|----|RT2|\ | N3 N4<ASE
may be undesirable. The ARA option allows for several methods to be | +---+ +---+ \ | +-----+ /
used which can limit shortcut connectivity. + \ ARA | ARA /
\+---+ +---+ +---+
|RT4|----|RT5|---|RT6|<ASBR
+---+ +---+ +---+
+ ARA / | |
| +---+ / | ARA +
N2|--|RT3|/ | +---+ |
| +---+ | |RT7|---|N5(ARA)
+ | +---+ |
------------------------|-------------------- +
Area 1.1.1.1 | OSPF Backbone
o [HEIN] proposes that shortcuts are setup by ingress routers Figure 2: Sample Area Topology
only after the sending data rate has passed a configured thres-
hold.
o ARA-capable routers may choose not to advertise their resolu- 3.3 Example 3: Multiple Logical Networks
tion information until some event has occured.
o Routers may be associated with "closed user shortcut groups" so The ARA option supports the existence of disjoint switched networks
that only routers that are within the same shortcut group may within an OSPF domain. To accomplish this, an ARA may include an iden-
set-up shortcuts to each other. This is done by coordinating the tifier (the logical network ID) for a specific switched network. When
configuration of a router's logical network ID list with the log- associations are added to the routing table during the OSPF routing
ical network ID advertised in ARA associations. table calculation (see the Section 9.1 "Adding ARA Routing Table
Extensions") only the associations that include a logical network ID
that matches one of the router's configured logical network IDs are
added to the routing table. This function may also be used to support
a variation of closed user groups so that shortcuts are limited to
those routers that are configured to be in the same logical network.
2.6 Acknowledgments The single-area topology described in Figure 3 below divides an OSPF
area into logical networks X and Y. In this example RT1, RT2 and RT4
support the ARA option and RT3 supports the Opaque LSA option only.
RT1 is connected to logical network (LN) X, RT2 is connected LN Y and
RT4 is connected to both LN X and LN Y. RT1, RT2 and RT4 all ori-
ginate R-ARAs.
The author would like to thank Atul Bansal, Lou Berger, Yiqun Cai, As a result of running their routing table calculation, RT1 and RT2
have entries for N1-N5 in their routing table. In both routing
tables, the N3-N5 entries reference the link-layer associations dis-
tributed in RT4's R-ARA. However, RT1's routing table does not refer-
ence RT2's link-layer associations for N2 and RT2's routing table does
not reference RT1's link-layer associations for N1 (i.e., they would
not be able to set up shortcuts to each other and would be forced to
use a hop-by-hop path to communicate).
Coltun, Heinanen [Page 6] + ARA (LN=X)
John Moy and the rest of the OSPF Working Group for the ideas and sup- | +---+ N3 N5
port they have given to this project. N1|--|RT1|\ \ N4 /
| +---+ \ \ | /
+ \ \|/
\+---+ +---+
|RT3|------------|RT4| ARA (LN=X,Y)
+---+ +---+
/
+ ARA (LN=Y)
| +---+ /
N2|--|RT2|/
| +---+
+
3.0 A Brief Comparison Of Address Resolution Models Figure 3: Sample Topology With Logical Networks
4.0 A Brief Comparison Of Address Resolution Models
Current models of inter-subnet address resolution have taken the form Current models of inter-subnet address resolution have taken the form
of a query/response protocol as in the case of [NHRP]. In this model of a query/response protocol as in the case of [NHRP]. In this model
the ingress device originates a resolution request which is forwarded the ingress device originates a resolution request which is forwarded
hop-by-hop through a series of NHRP servers towards the destination IP hop-by-hop through a series of NHRP servers towards the destination IP
address contained in the request. The the last-hop server (the one address contained in the request. The the last-hop server (the one
that is closest to the destination) responds to the request with the that is closest to the destination) responds to the request with the
link-layer address that it associates with the requested IP address. link-layer address that it associates with the requested IP address.
The address that is returned may be the address of the requested host The address that is returned may be the address of the requested host
system or the address of a router which is on the path to the destina- system or the address of a router which is on the path to the destina-
skipping to change at page 36, line ? skipping to change at page 10, line 22
o The target of a request may be a host or network addresses o The target of a request may be a host or network addresses
(excluding class D (multicast) networks). (excluding class D (multicast) networks).
o The response to the request allows the requesting entity to set o The response to the request allows the requesting entity to set
up a point-to-point shortcut. up a point-to-point shortcut.
Given the above characteristics, the query-response protocol may not Given the above characteristics, the query-response protocol may not
be the optimal mechanism for particular applications such as the one be the optimal mechanism for particular applications such as the one
described in [HEIN]. The ARA option has the following characteristics. described in [HEIN]. The ARA option has the following characteristics.
o Only routers participate in the ARA option. A router's o Only routers participate in the ARA option. A router's parti-
cipation in the ARA option is discovered through its address
Coltun, Heinanen [Page 7]
participation in the ARA option is discovered through its address
resolution advertisements. resolution advertisements.
o The ARA option does not require polling by the ingress device o The ARA option does not require polling by the ingress device
to detect topology and reachability changes. Changes in the to detect topology and reachability changes. Changes in the
topology and system reachability may result in packet loss (or topology and system reachability may result in packet loss (or
transient loops) for the OSPF convergence time. Additionally, transient loops) for the OSPF convergence time. Additionally,
since topology changes are determined as a result of OSPF's SPF since topology changes are determined as a result of OSPF's SPF
calculation (which results in loop-free paths), shortcuts derived calculation (which results in loop-free paths), shortcuts derived
from the ARA option can never result in stable routing loops. from the ARA option can never result in stable routing loops.
skipping to change at page 36, line ? skipping to change at page 11, line 8
o The ARA option allows the requesting entity to set up point- o The ARA option allows the requesting entity to set up point-
to-point shortcuts as well as shortcuts that join point-to- to-point shortcuts as well as shortcuts that join point-to-
multipoint and multipoint-to-point trees. multipoint and multipoint-to-point trees.
o Routers that run the ARA option can interoperate with systems o Routers that run the ARA option can interoperate with systems
running NHRP. running NHRP.
o The ARA option may easily be extended to support inter-subnet o The ARA option may easily be extended to support inter-subnet
multicast shortcuts. multicast shortcuts.
4.0 ARA Associations 5.0 ARA Components
The ARA option is comprised of several components including Address
Resolution Advertisements, the ARA association table, a logical net-
work ID List, routing table extensions and methods for restricting
shortcut connectivity. The following sections gives an overview of
these components.
5.1 Address Resolution Advertisements
The ARA option defines a set of link-state advertisements called
address resolution advertisements (ARAs). ARAs are used to distribute
the link-layer associations of routers and their directly connected
networks. ARAs are distributed within a single area and may be dis-
tributed between OSPF areas. ARA information is encapsulated in
Opaque LSAs (see [OPAQ] for a further description of Opaque LSAs).
Three LS Types (LS Type 9, 10 and 11) constitute the Opaque class of
link-state advertisements. Each of the three Opaque link-state types
have a scope associated with them so that distribution of the informa-
tion may be limited appropriately by the originator of the LSA.
Because the flooding scope for ARAs is always area local, ARAs are
encapsulated in LS Type 10 LSAs. Opaque LSAs have a sub-type which
identifies the specific information that is carried within the LSA.
ARA uses Opaque-types 1, 2, 3 and 4. See Section 7.0 for a further
description of the ARA packet formats.
5.2 ARA Association Table
A router implementing the ARA option maintains a table of link-layer
associations for each of its OSPF areas. The ARA Association Table is
used in calculating the ARA routing table extensions and by area
border routers in the inter-area ARA origination process. The indexes
for an entry in this table are the Vertex Type, Vertex ID and the Ver-
tex Originator. The Vertex Type identifies the type of IP topology
element that the link-layer information is being associated with
(i.e., a router or a network), the Vertex ID identifies a piece of the
OSPF topology (i.e., a router ID or an IP network number) and the Ver-
tex Originator is the Router ID of the router originating the ARA.
5.3 Logical Network ID List
An ARA capable router maintains a configured list of logical networks
IDs. This list represents the logical networks that a router is con-
nected to and may be used to restrict the set of devices that the
router may setup shortcuts to (see Section 4.5 "Restricting Shortcut
Connectivity"). The absence of entries in the router's list of Logi-
cal Network IDs means that the router will only activate ARA Associa-
tion Table entries with the default Logical Network ID (Logical Net-
work ID 0).
5.4 Routing Table Extensions
Associations are added to the routing table during the OSPF routing
table calculation (see Section 9.1 entitled "Adding ARA Routing Table
Extensions"). That is, in addition to the standard information fields
contained in the routing table (IP network number, IP mask, next-hop
interface, etc.), the routing table is extended to contain link-layer
associations. However, only 'active' link-layer associations are
added to the routing table. Associations containing a logical network
ID that matches a currently enabled entry in the router's list of log-
ical network IDs are considered to be active. Both active and non-
active link-layer associations may be included in inter-area ARAs that
are originated by an ABR.
The routing table (and its ARA routing table extensions) must be
recalculated if 1) there is a change to the OSPF topology, 2) there is
a change to the components in the ARA Association Table (see Section
10.0 "Receiving ARAs"), or 3) the router's logical network connec-
tivity has changed (e.g., the logical network ID list is modified or
the status of the router's connections to one of its logical networks
has changed).
The use of the routing table extensions are application specific and
beyond the scope of this document. See [HEIN] for an example of an
ARA user application.
5.5 Restricting Shortcut Connectivity
As a result of setting up shortcuts in an OSPF topology between ARA-
capable routers, the shortcut connectivity may become fully meshed.
In many environments this may be desirable whereas in in others this
may not be. The ARA option allows for several methods which can limit
shortcut connectivity.
o [HEIN] proposes that shortcuts are setup by ingress routers
only after the sending data rate has passed a configured thres-
hold.
o ARA-capable routers may choose not to advertise their resolu-
tion information until some event has occurred.
o Routers may be associated with "closed user shortcut groups" so
that only routers that are within the same shortcut group may
set-up shortcuts to each other. This is done by coordinating the
configuration of a router's logical network ID list with the log-
ical network ID advertised in ARA associations.
6.0 ARA Associations
The ARA option defines four types of advertisements. These include 1) The ARA option defines four types of advertisements. These include 1)
intra-area router associations, 2) intra-area network associations, 3) intra-area router associations, 2) intra-area network associations, 3)
inter-area network associations and 3) inter-area autonomous system inter-area network associations and 4) inter-area autonomous system
boundary router (ASBR) associations. Associations correspond to a boundary router (ASBR) associations. Associations correspond to a
piece of the OSPF topology. Intra-area router associations correspond piece of the OSPF topology. Intra-area router associations correspond
to link-layer reachability of a router within the local area, intra- to link-layer reachability of a router within the local area, intra-
area network associations correspond to the link-layer reachability of area network associations correspond to the link-layer reachability of
a router's directly connected network (also within the local area), a router's directly connected network (also within the local area),
inter-area network associations correspond to the link-layer reacha- inter-area network associations correspond to the link-layer reacha-
bility of a remote area router's directly connected network, and bility of a remote area router's directly connected network, and
inter-area ASBR associations correspond to ASBRs that are in remote inter-area ASBR associations correspond to ASBRs that are in remote
OSPF areas. Note that an inter-area network association may be ori- OSPF areas. Note that an inter-area network association may be ori-
ginated by an area border router (ABR) only if the network is not a ginated by an area border router (ABR) only if the network is not a
component of a configured net range. An ingress router can use these component of a configured net range. An ingress router can use these
associations as follows. associations as follows.
Coltun, Heinanen [Page 8]
Intra-area router associations are used to setup shortcuts to Intra-area router associations are used to setup shortcuts to
routers within the local area. Data sent over the shortcut will routers within the local area. Data sent over the shortcut will
be forwarded to destinations local to and beyond the router be forwarded to destinations local to and beyond the router
including ones that are in the local area, in a remote area or including ones that are in the local area, in a remote area or
external to the autonomous system. Destinations that are "beyond external to the autonomous system. Destinations that are "beyond
the router" are determined by the OSPF topology map. the router" are determined by the OSPF topology map.
Intra-area network associations (which may advertise hosts or Intra-area network associations (which may advertise hosts or
networks) are used to setup intra-area shortcuts to systems whose networks) are used to setup intra-area shortcuts to systems whose
addresses fall within the range of the advertised network. addresses fall within the range of the advertised network.
skipping to change at page 36, line ? skipping to change at page 14, line 8
Inter-area network associations (which may advertise a host or Inter-area network associations (which may advertise a host or
network address) are used to setup inter-area shortcuts to sys- network address) are used to setup inter-area shortcuts to sys-
tems whose address fall within the range of the advertised net- tems whose address fall within the range of the advertised net-
work. work.
Inter-area ASBR associations are used to setup shortcuts to ASBRs Inter-area ASBR associations are used to setup shortcuts to ASBRs
that are in a remote area. These shortcuts are used to send data that are in a remote area. These shortcuts are used to send data
to destinations that are external to the autonomous system and to destinations that are external to the autonomous system and
reachable via the ASBR. reachable via the ASBR.
5.0 Examples 7.0 Description Of ARA Packet Formats
5.1 Example 1: Intra-Area
Consider the sample single-area topology in Figure 1 below. In this
example RT1, RT2 and RT5 support the ARA option (by definition they
also support the Opaque LSA option) and RT4 supports the Opaque LSA
option only (this is necessary so that RT4 redistributes the ARAs ori-
ginated by RT1, RT2 and RT5). RT2 and RT5 have each originated a R-
ARA with an intra-area router association and RT5 has originated a N-
ARA with an intra-area network association for N5.
As a result of running the routing table calculation, RT1 has entries
for N1-N8 in its routing table. The entry for N2 references the
link-layer associations distributed in RT2's R-ARA, the entries for
N3, N4, N6, N7, N8 references the link-layer associations distributed
in RT5's R-ARA and the entry for N5 references the link-layer associa-
tions distributed in RT5's intra-area N-ARA.
Coltun, Heinanen [Page 9]
+ ARA
| +---+ N3 N5 (ARA)
N1|--|RT1|\ \ N4 /
| +---+ \ \ | /
+ \ \|/
\+---+ +---+
|RT4|------------|RT5|ARA
+---+ +---+
+ ARA / | N7
| +---+ / | /
N2|--|RT2|/ | /
| +---+ +---+ +---+/
+ |RT3|-----------|RT6|----N8
+---+ +---+
|
|
+---------+
N6
Figure 1: Sample Single-Area Toplogy
5.2 Example 2: Inter-Area
Consider the sample 2-area topology in Figure 2 below. In this exam-
ple RT1, RT2, RT3, RT4, RT6 and RT7 support the ARA option, and RT5
supports the Opaque option. N4 is an AS external route (which is
flooded to all areas) and RT6 is an ASBR. RT4 is an area-border
router and originates an LS Type-4 LSA on behalf of RT6 and a LS
Type-3 LSA for N5 into area 1.1.1.1.
Within area 1.1.1.1, RT1, RT2, RT3 and RT4 originate intra-area R-
ARAs. Within the backbone RT6 and RT7 originate intra-area R-ARAs and
R7 originates a N-ARA for N5. All backbone ARAs of have their the P-
bit set (this bit informs ABRs that the ARA may be propagated between
areas). RT4 originates an inter-area R-ARA for RT6 (which is an ASBR)
as well as an inter-area N-ARA for N5 into area 1.1.1.1 RT4 does not
originate an inter-area R-ARA for RT7 because it is not an ASBR.
As a result of running the routing table calculation, RT1 has entries
for N1-N5 in its routing table. The entry for N2 references the
link-layer associations distributed in RT3's R-ARA, the entry for N3
references the link-layer associations distributed in RT4's intra-area
R-ARA, the entry for N4 references the link-layer associations distri-
buted in RT4's inter-area R-ARA (indirectly referencing RT6's R-ARA)
and the entry for N5 references the link-layer associations
Coltun, Heinanen [Page 10]
distributed in RT4's inter-area N5 N-ARA.
+ ARA ARA |
| +---+ +---+ |
N1|--|RT1|----|RT2|\ | N3 N4<ASE
| +---+ +---+ \ | +-----+ /
+ \ ARA | ARA /
\+---+ +---+ +---+
|RT4|----|RT5|---|RT6|<ASBR
+---+ +---+ +---+
+ ARA / | |
| +---+ / | ARA +
N2|--|RT3|/ | +---+ |
| +---+ | |RT7|---|N5(ARA)
+ | +---+ |
------------------------|-------------------- +
Area 1.1.1.1 | OSPF Backbone
Figure 2: Sample Area Toplogy
5.3 Example 3: Multiple Logical Networks
The ARA option supports the existence of disjoint switched networks
within an OSPF domain. To accomplish this, an ARA may include an iden-
tifier (the logical network ID) for a specific switched network. When
associations are added to the routing table during the OSPF routing
table calculation (see the section 8.1 "Adding ARA Routing Table
Extensions") only the associations that include a logical network ID
that matches one of the router's configured logical network IDs are
added to the routing table. This function may also be used to support
a variation of closed user groups so that shortcuts are limited to
those routers that are configured to be in the same logical network.
The single-area topology described in Figure 3 below divides an OSPF
area into logical networks X and Y. In this example RT1, RT2 and RT4
support the ARA option and RT3 supports the Opaque LSA option only.
RT1 is connected to logical network (LN) X, RT2 is connected LN Y and
RT4 is connected to both LN X and LN Y. RT1, RT2 and RT4 all ori-
ginate R-ARAs.
As a result of running their routing table calculation, RT1 and RT2
have entries for N1-N5 in their routing table. In both routing
tables, the N3-N5 entries reference the link-layer associations dis-
tributed in RT4's R-ARA. However, RT1's routing table does not refer-
ence RT2's link-layer associations for N2 and RT2's routing table does
Coltun, Heinanen [Page 11]
not reference RT1's link-layer associations for N1 (i.e., they would
not be able to set up shortcuts to each other and would be forced to
use a hop-by-hop path to communicate).
+ ARA (LN=X)
| +---+ N3 N5
N1|--|RT1|\ \ N4 /
| +---+ \ \ | /
+ \ \|/
\+---+ +---+
|RT3|------------|RT4| ARA (LN=X,Y)
+---+ +---+
/
+ ARA (LN=Y)
| +---+ /
N2|--|RT2|/
| +---+
+
Figure 3: Sample Toplogy With Logical Networks
6.0 Description Of ARA Packet Formats
ARA LSAs (ARAs) include the information necessary to associate an IP ARA LSAs (ARAs) include the information necessary to associate an IP
entity (i.e., a router, network or host) with a link-layer address. entity (i.e., a router, network or host) with a link-layer address.
The ARA option allows further refinement so that an association may The ARA option allows further refinement so that an association may
additionally include information about QoS control services and link- additionally include information about QoS control services and link-
layer functionality (e.g., for Point-to-MultiPoint and MultiPoint-to- layer functionality (e.g., for Point-to-MultiPoint and MultiPoint-to-
point connections). ARA advertisements may also include a logical point connections). ARA advertisements may also include a logical
network identifier field, which is used when multiple switched net- network identifier field, which is used when multiple switched net-
works are present within the OSPF domain. works are present within the OSPF domain.
The ARA format allows more than one equivalent association to been The ARA format allows more than one equivalent association to be
advertised by a router for a specific vertex. Equivalent associations advertised by a router for a specific vertex. Equivalent associations
are ones that have identical link service type, integrated service are ones that have identical link service type, integrated service
type and logical network identifier fields, but have different resolu- type and logical network identifier fields, but have different resolu-
tion information. Associations can include a preference which identi- tion information. Associations can include a preference which identi-
fies the advertising router's relative preference for the equivalent fies the advertising router's relative preference for the equivalent
associations. associations (a higher numeric preference denotes a better choice).
ARA information is encapsulated in Opaque LSAs. Three LS Types (LS ARA information is encapsulated in Opaque LSAs. Three LS Types (LS
Type 9, 10 and 11) constitute the Opaque class of link-state adver- Type 9, 10 and 11) constitute the Opaque class of link-state adver-
tisements. Each of the three Opaque link-state types have a scope tisements. Each of the three Opaque link-state types have a scope
associated with them so that distribution may be limited appropriately associated with them so that distribution may be limited appropriately
Coltun, Heinanen [Page 12]
by the originator of the LSA. Opaque LSAs have a sub-type which iden- by the originator of the LSA. Opaque LSAs have a sub-type which iden-
tifies the specific information that is carried within the LSA. The tifies the specific information that is carried within the LSA. The
ARA Opaque types are Opaque-type 1 - 4. Because the flooding scope ARA Opaque types are Opaque-types 1 - 4. Because the flooding scope
for ARAs is always area local, ARAs are encapsulated in LS Type 10 for ARAs is always area local, ARAs are encapsulated in LS Type 10
LSAs. LSAs.
6.1 Vertex Types And Vertex Identifiers 7.1 Vertex Types And Vertex Identifiers
The Vertex Type identifies the piece of IP topology that the link- The Vertex Type identifies the piece of IP topology that the link-
layer information is being associated with. The Vertex Type may be a layer information is being associated with. The Vertex Type may be a
router or a network (a host is considered a network with a mask of router or a network (a host is considered a network with a mask of
255.255.255.255). 255.255.255.255).
Vertex Type 1 ARAs advertise intra-area router resolution associa- Vertex Type 1 ARAs advertise intra-area router resolution associa-
tions. These associations distribute the router's link-layer attach- tions. These associations distribute the router's link-layer attach-
ments. A Vertex Type of 1 is identified by an Opaque type of 1. The ments. A Vertex Type of 1 is identified by an Opaque type of 1. The
Vertex Identifier for a R-ARA is the advertising router field in the Vertex Identifier for a R-ARA is the advertising router field in the
ARA header. ARA header.
Vertex Type 2 ARAs advertise intra-area IP network address resolution Vertex Type 2 ARAs advertise intra-area IP network address resolution
associations. These associations distribute the link-layer associa- associations. These associations distribute the link-layer associa-
tions for a router's directly connected network. A Vertex Type of 2 tions for a router's directly connected networks. A Vertex Type of 2
is identified by an Opaque type of 2. The Vertex Identifier (the net- is identified by an Opaque type of 2. The Vertex Identifier (the net-
work and mask) for a N-ARA is contained in the body of the advertise- work and mask) for a N-ARA is contained in the body of the advertise-
ment. N-ARAs may only contain a single network (i.e., lists of net- ment. N-ARAs may only contain a single network (i.e., lists of net-
works are not permitted). works are not permitted).
Vertex Type 3 ARAs advertise inter-area IP network address resolution Vertex Type 3 ARAs advertise inter-area IP network address resolution
associations. These associations are used to distribute link-layer associations. These associations are used to distribute link-layer
associations for networks into remote areas. A Vertex Type of 3 is associations for networks into remote areas. A Vertex Type of 3 is
identified by an Opaque type of 3. The Vertex Identifier (the network identified by an Opaque type of 3. The Vertex Identifier (the network
and mask) for a inter-area N-ARA is contained in the body of the and mask) for an inter-area N-ARA is contained in the body of the
advertisement. N-ARAs may only identify a single network (i.e., lists advertisement. N-ARAs may only identify a single network (i.e., lists
of networks are not permitted). Vertex Type 3 N-ARAs are originated of networks are not permitted). Vertex Type 3 N-ARAs are originated
by an area border router (ABR) into an area when 1) the ABR originates by an area border router (ABR) into an area when 1) the ABR originates
a type-3 LSA for the network into the target area, 2) the network is a type-3 LSA for the network into the target area, 2) the network is
not included in any of the area border router's configured area not included in any of the area border router's configured area
ranges, 3) there is a N-ARA for the network in the source area, 4) the ranges, 3) there is a N-ARA for the network in the source area, 4) the
source N-ARA may be an intra or inter-area N-ARA. If it is an intra- source N-ARA may be an intra or inter-area N-ARA. If it is an intra-
area N-ARA the P-bit must be set in its options field. The setting of area N-ARA the P-bit must be set in its options field. The setting of
the P-bit by the originator denotes that the associations contained in the P-bit by the originator denotes that the associations contained in
the N-ARA are allowed to be propagated into other areas. the N-ARA are allowed to be propagated into other areas. The default
setting for the P-bit is off.
Vertex Type 4 ARAs advertise inter-area router address resolution Vertex Type 4 ARAs advertise inter-area router address resolution
associations. These R-ARAs redistribute associations for ASBRs into associations. These R-ARAs redistribute associations for ASBRs into
remote areas. A Vertex Type of 4 is identified by an Opaque type of remote areas. A Vertex Type of 4 is identified by an Opaque type of
4. The Vertex Identifiers for an inter-area R-ARA are the advertising 4. The Vertex Identifiers for an inter-area R-ARA are the advertising
router field of the ARA header and the ASBR Router ID found in the router field of the ARA header and the ASBR Router ID found in the
Coltun, Heinanen [Page 13]
body of the ARA. Vertex Type 4 R-ARAs are originated by an area body of the ARA. Vertex Type 4 R-ARAs are originated by an area
border router (ABR) into a target area when 1) the ABR originates a border router (ABR) into a target area when 1) the ABR originates a
type-4 LSA for the ASBR into the target area, 2) there is a R-ARA for type-4 LSA for the ASBR into the target area, 2) there is a R-ARA for
the network in the source area, 3) the source R-ARA may be an intra or the network in the source area, 3) the source R-ARA may be an intra or
inter-area R-ARA. If the source R-ARA is an intra-area R-ARA its P- inter-area R-ARA. If the source R-ARA is an intra-area R-ARA its P-
bit must be set in the options field. The setting of the P-bit by the bit must be set in the options field. The setting of the P-bit by the
originator denotes that the associations contained in the R-ARA are originator denotes that the associations contained in the R-ARA are
allowed to be propagated into other areas. allowed to be propagated into other areas. The default setting for
the P-bit is off.
If a router wishes to advertise several associations for a single ver- If a router wishes to advertise several associations for a single ver-
tex it has two options. It may originate multiple (N or R) ARAs each tex it has two options. It may originate multiple (N or R) ARAs each
containing different associations or it may originate a single (N or containing different associations or it may originate a single (N or
R) ARA containing a list of associations. An implementation must not R) ARA containing a list of associations. An implementation must not
include identical associations in more than one ARA. include identical associations in more than one ARA.
7.0 Distribution Of ARA Information 8.0 Distribution Of ARA Information
In general, OSPF is composed of two components. It's transport com- In general, OSPF is composed of two components. It's transport com-
ponent handles adjacency formation and reliable distribution of topol- ponent handles adjacency formation and reliable distribution of topol-
ogy information. The second component tracks topology changes and ogy information. The second component tracks topology changes and
organizes the topology information that has been gathered from other organizes the topology information that has been gathered from other
routers into to a topology map. This map is used to build the router's routers into to a topology map. This map is used to build the router's
routing table. The ARA option uses both the OSPF transport component routing table. The ARA option uses both the OSPF transport component
and of the topology map component. and the topology map component.
ARA uses the OSPF Opaque LSA as defined in [OPAQ] for distribution of ARA uses the OSPF Opaque LSA as defined in [OPAQ] for distribution of
resolution information. The Opaque LSA is an optional mechanism to resolution information. The Opaque LSA is an optional mechanism to
allow for distribution of opaque information which may be used allow for distribution of information which may be used directly by
directly by OSPF or by other protocols and mechanisms. Opaque LSAs OSPF or by other protocols and mechanisms. Opaque LSAs use the stan-
use the standard OSPF link-state database flooding mechanisms for dis- dard OSPF link-state database flooding mechanisms for distribution.
tribution. Each of the three Opaque types (LS Types 9, 10 and 11) Each of the three Opaque types (LS Types 9, 10 and 11) have a scope
have a scope associated with them (link-local, area-local or domain- associated with them (link-local, area-local or domain-wide, respec-
wide, respectively). Scoping provides an application with a method to tively). Scoping provides an application with a method to limit the
limit the range of information distribution. ARA information is dis- range of information distribution. ARA information is distributed
tributed with area-local scope (i.e., ARA information is encapsulated with area-local scope (i.e., ARA information is encapsulated in LS
in LS Type 10 LSAs). Type 10 LSAs).
The ARA option uses the topology map component of OSPF to validate the The ARA option uses the topology map component of OSPF to validate the
information that is received by the distribution mechanism and to information that is received by the distribution mechanism and to
install the associations into the ARA routing table extensions. Vali- install the associations into the ARA routing table extensions. Vali-
dation is necessary because topology information contained in the OSPF dation is necessary because topology information contained in the OSPF
link-state database may be stale (e.g., the originator of the informa- link-state database may be stale and therefore unusable (e.g., the
tion is no longer reachable). originator of the information is no longer reachable).
It is envisioned that an implementor designs an ARA user application It is envisioned that an implementor designs an ARA user application
interface which facilitates 1) flooding of ARA information to other interface which facilitates 1) flooding of ARA information to other
routers in the OSPF network, 2) receiving ARA information from other routers in the OSPF network, 2) receiving ARA information from other
Coltun, Heinanen [Page 14]
routers in the OSPF network and 3) determines the validity (and change routers in the OSPF network and 3) determines the validity (and change
of validity) of ARA information. of validity) of ARA information.
For the realization of 1 above, an implementation must provide an API For the realization of 1 above, an implementation must provide an API
to facilitate the ARA user application's "hand off" of resolution to facilitate the ARA user application's "hand off" of resolution
information to its local OSPF entity which will then be distributed information to its local OSPF entity who will then distribute the
throughout the OSPF topology. In addition, the API must support the information throughout the OSPF topology. In addition, the API must
purging of associations that were previously originated by the router support the purging of associations that were previously originated by
if they are no longer valid and send out new versions when the associ- the router if they are no longer valid and send out new versions when
ation information has changed. the association information has changed.
For the realization of 2 and 3 above, this document extends the rout- For the realization of 2 and 3 above, this option extends the rout-
ing table to include the associations that have been advertised by the ing table to include the associations that have been advertised by the
ARA capable routers (i.e,. the routing table provides the API for the ARA capable routers (i.e,. the routing table provides the API for the
ARA user application). That is, in addition to the standard informa- ARA user application). That is, in addition to the standard informa-
tion fields contained in the routing table (i.e., IP network number, tion fields contained in the routing table (i.e., IP network number,
IP mask, next-hop interface, etc.), the routing table is extended to IP mask, next-hop interface, etc.), the routing table is extended to
contain link-layer associations. The associations are added to the contain link-layer associations. The associations are added to the
routing table during the OSPF routing table calculation. Section 8.0 routing table during the OSPF routing table calculation. Section 8.0
defines the mechanism to calculate the ARA routing table extensions. defines the mechanism to calculate the ARA routing table extensions.
The use of the extensions are ARA user application specific and beyond The use of the extensions are ARA user application specific and beyond
the scope of this document. See [HEIN] for an example of an ARA user the scope of this document. See [HEIN] for an example of an ARA user
application. application.
7.1 Originating Inter-Area ARAs 8.1 Originating Inter-Area ARAs
Inter-area ARAs provide a mechanism to distribute link-layer associa- Inter-area ARAs provide a mechanism to distribute link-layer associa-
tions to other areas. Inter-area ARAs (consisting of Vertex Type-3 tions to other areas. Inter-area ARAs (consisting of Vertex Type-3
and Type-4 ARAs) have a one-to-one correspondence to Summary LSAs (LS and Type-4 ARAs) have a one-to-one correspondence to Summary LSAs (LS
type-3 and type-4 LSAs). Vertex Type-3 ARAs advertise the link-layer type-3 and type-4 LSAs). Vertex Type-3 ARAs advertise the link-layer
associations of IP networks whereas Vertex Type-4 ARAs advertise the associations of IP networks whereas Vertex Type-4 ARAs advertise the
link-layer associations of autonomous system boundary routers (ASBR). link-layer associations of autonomous system boundary routers (ASBR).
As with Summary LSAs, inter-area ARAs are originated by area border As with Summary LSAs, inter-area ARAs are originated by area border
routers into a target area based on a set of conditions in the source routers into a target area based on a set of conditions in the source
area. For both intra and inter-are ARAs, there may be more than one area. For both intra and inter-are ARAs, there may be more than one
skipping to change at page 36, line ? skipping to change at page 17, line 32
tions (recall that an implementation must not include identical asso- tions (recall that an implementation must not include identical asso-
ciations in more than one ARA). Inter-area ARAs must include, in one ciations in more than one ARA). Inter-area ARAs must include, in one
or more ARA, all of the link-layer associations contained in their or more ARA, all of the link-layer associations contained in their
'trigger' ARAs (see below for a description of the conditions for ABRs 'trigger' ARAs (see below for a description of the conditions for ABRs
to trigger inter-area ARAs). to trigger inter-area ARAs).
The link-layer associations that comprise the 'trigger' ARAs (in the The link-layer associations that comprise the 'trigger' ARAs (in the
source area) may include logical network IDs that are not in the ABR's source area) may include logical network IDs that are not in the ABR's
configured list of logical network IDs (i.e., the ABR itself may not configured list of logical network IDs (i.e., the ABR itself may not
be able to set up a shortcut because it may be connected to a disjoint be able to set up a shortcut because it may be connected to a disjoint
set of logical networks). Despite the ABR's logical network set of logical networks). Despite the ABR's logical network affilia-
tion, all trigger ARAs' link-layer associations are included in the
Coltun, Heinanen [Page 15] newly originated inter-area ARAs.
affiliation, all trigger ARAs' link-layer associations are included in
the newly originated inter-area ARAs.
The origination process for type-3 and type-4 Summary LSAs (as dis- The origination process for type-3 and type-4 Summary LSAs (as dis-
cussed in section 12.4.3 of [OSPF]) consists of an ABR evaluating each cussed in Section 12.4.3 of [OSPF]) consists of an ABR evaluating each
entry in the routing table. If an entry satisfies a set of condi- entry in the routing table. If an entry satisfies a set of condi-
tions, the ABR originates a Summary LSA into the target area. tions, the ABR originates a Summary LSA into the target area.
This process is extended for inter-area ARA origination so that when a This process is extended for inter-area ARA origination so that when a
Summary LSA is originated into an area by an ABR, the conditions for Summary LSA is originated into an area by an ABR, the conditions for
the origination of inter-area ARAs are also evaluated. When these con- the origination of inter-area ARAs are also evaluated. When these con-
ditions are satisfied, an inter-area ARA is originated into the target ditions are satisfied, an inter-area ARA is originated into the target
area. Conversely, when a Summary route is withdrawn from an area by area. Conversely, when a Summary route is withdrawn from an area by
an ABR and a corresponding ARA was previously originated into the an ABR and a corresponding ARA was previously originated into the
area, the ARA must be withdrawn from the target area. The following area, the ARA must be withdrawn from the target area. The following
skipping to change at page 36, line ? skipping to change at page 18, line 35
the 'trigger' network's IP network number and mask. The Vertex the 'trigger' network's IP network number and mask. The Vertex
Originator is the router ID of the trigger network's originator. Originator is the router ID of the trigger network's originator.
o The set of link-layer associations that are to be included in o The set of link-layer associations that are to be included in
the advertisement are contained in the ARA Association Table the advertisement are contained in the ARA Association Table
entry. However, if the network that triggered the origination of entry. However, if the network that triggered the origination of
the type-3 LSA is an intra-area route, only the link-layer asso- the type-3 LSA is an intra-area route, only the link-layer asso-
ciations whose ARA's P-bit were set may be advertised. (if no ciations whose ARA's P-bit were set may be advertised. (if no
associations have their P-bit set the inter-area N-ARA must not associations have their P-bit set the inter-area N-ARA must not
be originated). The setting of the P-bit in the N-ARA by its be originated). The setting of the P-bit in the N-ARA by its
Coltun, Heinanen [Page 16]
originator gives the ABRs permission to propagate the resolution originator gives the ABRs permission to propagate the resolution
information into other areas. information into other areas.
Inter-area R-ARAs redistribute link-layer associations for ASBRs to Inter-area R-ARAs redistribute link-layer associations for ASBRs to
other areas. Inter-area R-ARAs have a Vertex Type of 4. The Vertex other areas. Inter-area R-ARAs have a Vertex Type of 4. The Vertex
Identifiers for an inter-area R-ARA are 1) the advertising router Identifiers for an inter-area R-ARA are 1) the advertising router
field of the ARA header and 2) the ASBR's Router ID which is found in field of the ARA header and 2) the ASBR's Router ID which is found in
the body of the ARA. Vertex Type-4 R-ARAs are originated by an area the body of the ARA. Vertex Type-4 R-ARAs are originated by an area
border router (ABR) into an area if the following conditions are met. border router (ABR) into an area if the following conditions are met.
skipping to change at page 36, line ? skipping to change at page 19, line 23
the advertisement are contained in the ARA Association Table the advertisement are contained in the ARA Association Table
entry. However, if the router advertisement that triggered the entry. However, if the router advertisement that triggered the
origination of the type-3 LSA is an intra-area route, only the origination of the type-3 LSA is an intra-area route, only the
link-layer associations whose ARA's P-bit are set may be adver- link-layer associations whose ARA's P-bit are set may be adver-
tised in the newly originated inter-area R-ARA (if no associa- tised in the newly originated inter-area R-ARA (if no associa-
tions have their P-bit set the inter-area N-ARA must not be ori- tions have their P-bit set the inter-area N-ARA must not be ori-
ginated). The setting of the P-bit in the R-ARA by its origina- ginated). The setting of the P-bit in the R-ARA by its origina-
tor gives the ABRs permission to propagate the resolution infor- tor gives the ABRs permission to propagate the resolution infor-
mation into other areas. mation into other areas.
8.0 ARA Routing Table Extensions 9.0 ARA Routing Table Extensions
OSPF determines reachability and topology changes by performing the OSPF determines reachability and topology changes by performing the
algorithms described in the section 16 of [OSPF] entitled "Calculation algorithms described in the Section 16 of [OSPF] entitled "Calculation
of the routing table". ARAs are included in this calculation for the of the routing table". ARAs are included in this calculation for the
purpose of binding link-layer associations to IP routing table purpose of binding link-layer associations to IP routing table
entries. entries.
A link-layer association consists of the list of link-layer addresses, A link-layer association consists of the list of link-layer addresses,
link-layer service types and other link-layer objects such as Point- link-layer service types and other link-layer objects such as Point-
Coltun, Heinanen [Page 17]
to-MultiPoint call identifiers and QoS service specific information to-MultiPoint call identifiers and QoS service specific information
(see Appendix A for a more complete description of the specific link- (see Appendix A for a more complete description of the specific link-
layer information distributed in ARAs). The associations that are layer information distributed in ARAs). The associations that are
bound to a routing table entry are the associations that are 1) bound to a routing table entry are the associations that are 1)
closest to the destination and 2) are on the same logical network as closest to the destination and 2) are on the same logical network as
the calculating router (as identified by the logical network ID). The the calculating router (as identified by the logical network ID). The
closest associations are determined during to the construction of the closest associations are determined during to the construction of the
OSPF topology map. The associations that are bound to the routing OSPF topology map. The associations that are bound to the routing
table entries are subsequently used by the ARA user application to table entries are subsequently used by the ARA user application (e.g.,
setup shortcut paths. a shortcut manager) to setup shortcut paths.
Multiple link-layer associations may be bound to a single routing
table entry when multiple link-layer association are advertised by the
source or when the routing table calculation discovers equal cost
paths. These may be used as alternate entries (e.g., when a call set
up to a one association fails another may be used) or may be used to
set up equal-cost shortcuts.
Because a link-layer association may be bound to more than one entry Because a link-layer association may be bound to more than one entry
in the routing table, an ARA implementation keeps a table of ARA in the routing table, an ARA implementation keeps a table of ARA
derived link-layer associations which is referenced by the routing derived link-layer associations which is referenced by the routing
table entry. Each area has its own ARA Association table. An entry table entry. Each area has its own ARA Association table. An entry
in the ARA Association Table consists of a list of all association for in the ARA Association Table consists of a list of all associations
a specific vertex and vertex type by a specific originator; the lookup for a specific vertex and vertex type by a specific originator; the
keys for an entry in the table include the Vertex Type, Vertex ID and lookup keys for an entry in the table include the Vertex Type, Vertex
the Vertex Originator. ID and the Vertex Originator.
8.1 Adding ARA Routing Table Extensions 9.1 Adding ARA Routing Table Extensions
Section 16 of the OSPF specification is modified for the purpose of Section 16 of the OSPF specification is modified for the purpose of
adding the ARA routing table extensions. Transit vertex data struc- adding the ARA routing table extensions. Transit vertex data struc-
tures and the internal representation of Type-3, Type-4 and Type-5 tures and the internal representation of Type-3, Type-4 and Type-5
LSAs are extended to be able to reference a list of link-layer associ- LSAs are extended to be able to reference a list of link-layer associ-
ations (i.e., they have a reference to the ARA Association Table). ations (i.e., they have a reference to the ARA Association Table).
The vertex and LSA's list of link-layer associations are added to the The vertex and LSA's list of link-layer associations are added to the
routing table along with the entry. routing table along with the entry.
Prior to running the intra-area route calculation the ARA Association Prior to running the intra-area route calculation the ARA Association
Table is examined. Associations containing a logical network ID that Table is examined. Associations containing a logical network ID that
matches an entry in the router's list of logical network IDs are matches an entry in the router's list of logical network IDs are
marked 'active'. marked 'active'.
8.1.1 Modifications To The Intra-Area Route Calculation 9.1.1 Modifications To The Intra-Area Route Calculation
The intra-area route calculation is enhanced (specifically section The intra-area route calculation is enhanced (specifically Section
16.1 step 3) as follows. 16.1 step 3 of [OSPF]) as follows.
o Call the vertex that is about to be added to the SPF tree ver- o Call the vertex that is about to be added to the SPF tree ver-
tex M. If vertex M was originated by the calculating router skip tex M. If vertex M was originated by the calculating router skip
this procedure. this procedure.
o If vertex M is a transit network vertex lookup the link-layer o If vertex M is a transit network vertex lookup the link-layer
association entry in the ARA Association Table. This entry's association entry in the ARA Association Table. This entry's
Coltun, Heinanen [Page 18]
Vertex Type will be 2, the Vertex Identifier will be vertex M's Vertex Type will be 2, the Vertex Identifier will be vertex M's
network and mask, the Vertex Originator will be vertex M's Router network and mask, the Vertex Originator will be vertex M's Router
ID and its area ID will be the one that is associated with the ID and its area ID will be the one that is associated with the
shortest-path calculation. shortest-path calculation.
o If an active entry is found, reference this entry in vertex M's o If an active entry is found, copy this entry to vertex M's
link-layer association field. link-layer association list.
o If vertex M is a router vertex lookup the an entry in the ARA o If vertex M is a router vertex lookup the an entry in the ARA
Association Table. This entry's Vertex Type will be 1, the Ver- Association Table. This entry's Vertex Type will be 1, the Ver-
tex Identifier will be vertex M's advertising router, the Vertex tex Identifier will be vertex M's advertising router, the Vertex
Originator will be vertex M's advertising router and its area ID Originator will be vertex M's advertising router and its area ID
will be the one that is associated with the shortest-path calcu- will be the one that is associated with the shortest-path calcu-
lation. lation.
o If an an active entry is found, reference this entry in vertex o If an an active entry is found, add this entry to vertex M's
M's link-layer association field. link-layer association list.
o If no active link-layer association entries are found, and ver- o If no active link-layer association entries are found, and ver-
tex M's parent vertex has link-layer association information, tex M's parent vertex has link-layer association information,
vertex M inherits it's parent vertex's information (else the vertex M inherits it's parent vertex's information (else the
information field is left blank). information field is left blank).
o When vertex M is added to the routing table, copy the active o When vertex M is added to the routing table, copy the active
associations from vertex M's link-layer association list into the associations from vertex M's link-layer association list into the
routing table entry's link-layer association field. routing table entry's link-layer association field.
The following describes the enhancements to section 16.1 step 2 of The following describes the enhancements to Section 16.1 step 2 of
[OSPF] which adds intra-area stub networks to the routing table. [OSPF] which adds intra-area stub networks to the routing table.
o Before adding the stub network to the routing table lookup the o Before adding the stub network to the routing table lookup the
entry in the ARA Association Table. This entry's Vertex Type entry in the ARA Association Table. This entry's Vertex Type
will be 2, the Vertex Identifier will consist of the network and will be 2, the Vertex Identifier will consist of the network and
mask of the stub network, the Vertex Originator will be the mask of the stub network, the Vertex Originator will be the
advertising router's Router ID and its area ID will be the one advertising router's Router ID and its area ID will be the one
that is associated with the shortest-path calculation. that is associated with the shortest-path calculation.
o If an active entry is found copy the entry's active association o If an active entry is found copy the entry's active association
information into the routing table entry's link-layer association information into the routing table entry's link-layer association
field. field.
o If an entry is not found and the stub network's advertising o If an entry is not found and the stub network's advertising
router vertex has link-layer association information, the routing router vertex has link-layer association information, the routing
table entry will inherit the advertising router's information table entry will inherit the advertising router's information
(else the information field is left blank). (else the information field is left blank).
Coltun, Heinanen [Page 19] 9.1.2 Modifications To The Inter-Area Route Calculation
8.1.2 Modifications To The Inter-Area Route Calculation
The following describes the enhancements to OSPF sections 16.2, 16.3, The following describes the enhancements to OSPF Sections 16.2, 16.3,
16.5 which calculate inter-area routes. Before the destination associ- 16.5 which calculate inter-area routes. Before the destination associ-
ated with the LSA is added to the routing table the following is per- ated with the LSA is added to the routing table the following is per-
formed. formed.
o If the LSA is a Type-3 Summary LSA, lookup the entry in the ARA o If the LSA is a Type-3 Summary LSA, lookup the entry in the ARA
Association Table. This entry's Vertex Type will be 3, the Vertex Association Table. This entry's Vertex Type will be 3, the Vertex
Identifier will be the Summary LSA's network and mask, the Vertex Identifier will be the Summary LSA's network and mask, the Vertex
Originator will be the advertising router's Router ID and its Originator will be the advertising router's Router ID and its
area ID will be the one that is associated with the shortest-path area ID will be the one that is associated with the shortest-path
calculation. If an active entry is found copy the entry's active calculation. If an active entry is found copy the entry's active
skipping to change at page 36, line ? skipping to change at page 22, line 28
association field. association field.
o If an active entry was not found for the type-3 or type-4 LSA, o If an active entry was not found for the type-3 or type-4 LSA,
locate the area border router (ABR) that originated the adver- locate the area border router (ABR) that originated the adver-
tisement. If link-layer association information is available for tisement. If link-layer association information is available for
the ABR entry, copy the contents of the ABR's link-layer associa- the ABR entry, copy the contents of the ABR's link-layer associa-
tion information field into the routing table entry's link-layer tion information field into the routing table entry's link-layer
association field. If no active entry was found for the ABR the association field. If no active entry was found for the ABR the
routing table entry's information field will be left blank. routing table entry's information field will be left blank.
8.1.3 Modifications To The AS External Route Calculation 9.1.3 Modifications To The AS External Route Calculation
The following describes the enhancements to OSPF sections 16.4 and The following describes the enhancements to OSPF Sections 16.4 and
16.6 which calculate AS external routes. Before the destination asso- 16.6 which calculate AS external routes. Before the destination asso-
ciated with the LSA is added to the routing table the following is ciated with the LSA is added to the routing table the following is
performed. performed.
o If the LSA has a forwarding address, look up the forward o If the LSA has a forwarding address, look up the forward
address in the routing table (this will be an internal OSPF address in the routing table (this will be an internal OSPF
route). Copy the contents of the route's link-layer association route). Copy the contents of the route's link-layer association
information field into the external route's routing table entry's information field into the external route's routing table entry's
link-layer association field. The forwarding address' link-layer link-layer association field. The forwarding address' link-layer
Coltun, Heinanen [Page 20]
association information may have been added as a result of pro- association information may have been added as a result of pro-
cessing intra-area or inter-area N-ARAs. cessing intra-area or inter-area N-ARAs.
o If the LSA does not have a forwarding address, copy the con- o If the LSA does not have a forwarding address, copy the con-
tents of the advertising ASBR's link-layer association informa- tents of the advertising ASBR's link-layer association informa-
tion field into the routing table entry's link-layer association tion field into the routing table entry's link-layer association
field. The ASBR's link-layer association information may have field. The ASBR's link-layer association information may have
been added as a result of processing intra-area or inter-area R- been added as a result of processing intra-area or inter-area R-
ARAs. ARAs.
9.0 Receiving ARAs 9.2 Routing Table Extension Completion
After the ARA has been processed according to section 13 of [OSPF] the Upon completing the calculation of ARA routing table extensions the
entity that manages shortcuts must be informed so that it can reevalu-
ate existing shortcuts and determine if new shortcuts are to be setup.
Reevaluation of existing shortcuts is necessary so that the router can
determine if shortcuts that it has previously set up are no longer on
the path to their target destinations. Packets that are sent on these
invalid shortcuts may result in packet loss or forwarding loops.
Reevaluating existing shortcuts requires comparing the shortcut's
currently active link-layer associations with the link-layer associa-
tions that have just been derived. If a destination is no longer in
the routing table or no longer has an association, the shortcut must
be terminated. If there is a mismatch between the associations
currently being used by an active shortcut (for a specific target net-
work) and the associations that have just been derived, the currently
active shortcut must be terminated and if warranted, a new shortcut
must be set up.
An implementation may want to consider methods for dampening the
number of existing shortcuts that are terminated and set up immedi-
ately following a route calculation. One dampening model would be to
configure a maximum number of changes per time period. If the number
of changes exceeds the maximum number, the router must either stop
forwarding on invalid paths (dropping all packets for the destinations
unsing invalid shortcuts) or revert to hop-by-hop forwarding until the
invalid shortcuts are terminated and new ones have been set up.
An enhancement to this model would be to allow "pretty good" shortcuts
to exist for a some time after a route calculation has completed.
That is, the list of associations for a destination would be extended
to include both the associations that are closest to the target net-
work and ones that are on the path towards the destination. To imple-
ment this, during the calculation of the ARA routing table extensions,
the list of associations for a specific target network would be
extended to inherit all associations from it's parents (in addition to
the associations that it has determined to be closest to the target
network). After running the calculation the shortcut manager would
check each the of the currently active shortcut's associations:
o If the associations currently being used by the shortcut is the
closest one to the target network, evaluate the next shortcut.
o If the associations currently being used by the shortcut are
not the closest ones to the target network but are on the path to
the target network the shortcut may remain.
o If the associations currently being used by the shortcut are
not on the path to the target network, forwarding must cease on
the shortcut and the shortcut must be terminated.
10.0 Receiving ARAs
After the ARA has been processed according to Section 13 of [OSPF] the
ARA has been determined to be 1) a new ARA, 2) a newer instance of an ARA has been determined to be 1) a new ARA, 2) a newer instance of an
existing ARA with the same contents, 3) a newer instance with dif- existing ARA with the same contents, 3) a newer instance with dif-
ferent contents, or 4) an ARA that is being withdrawn by it's origina- ferent contents, or 4) an ARA that is being withdrawn by it's origina-
tor. Actions need to be taken if the ARA is new, the contents of the tor. If the ARA is new, the contents of the ARA have changed or the
ARA have changed or the ARA is being withdrawn. ARA is being withdrawn, the following actions must be taken.
o Lookup the entry for the ARA in the ARA Association Table. If o Lookup the entry for the ARA in the ARA Association Table. If
there is no existing entry, create one which contains the associ- there is no existing entry and the ARA has determined to be new,
ations found in the ARA. The newly added associations should create an entry in the ARA Association Table which contains the
reflect the state of the ARA's P-bit. associations found in the ARA. The newly added associations
should reflect the state of the ARA's P-bit.
o If the there is an existing entry and the newly received ARA o If the there is an existing entry and the newly received ARA
contents have changed modify the entry to reflect the associa- contents have changed modify the entry to reflect the associa-
tions found in the newly received ARA. The changed associations tions found in the newly received ARA. The changed associations
should reflect the state of the ARA's P-bit. should reflect the state of the ARA's P-bit.
o If the ARA is being withdrawn and there is an existing entry, o If the ARA is being withdrawn and there is an existing entry,
remove the associations from the link-layer entry that were pre- remove the associations from the link-layer entry that were pre-
viously included in the ARA. If the contents of the table entry viously included in the ARA. If the contents of the table entry
is now empty remove the entry from the table. is now empty remove the entry from the table.
If the above process has resulted in a modification to the ARA table, If the above process has resulted in a modification to the ARA table,
the SPF calculation must be rescheduled. (see section 8.1 entitled the SPF calculation must be rescheduled (see Section 8.1 entitled
"Adding ARA Routing Table Extensions"). If the receiving router is an "Adding ARA Routing Table Extensions"). If the receiving router is an
ABR the inter-area origination process must be scheduled to be run ABR the inter-area origination process must be scheduled to be run
following the SPF calculation (see section 7.1 entitled "Originating following the SPF calculation (see Section 8.1 entitled "Originating
Inter-area ARAs"). Inter-area ARAs").
10.0 Additional Data Structures And APIs 11.0 Additional Data Structures And APIs
Coltun, Heinanen [Page 21]
This section lists the additional data structures and APIs needed to This section lists the additional data structures and APIs needed to
support the OSPF ARA option. support the OSPF ARA option.
o The implementation must support the Opaque LSA option as o The implementation must support the Opaque LSA option as
defined in [OPAQ]. defined in [OPAQ].
o A configuration flag to enable the OSPF ARA option. o A configuration knob to enable the OSPF ARA option.
o A router implementing the ARA option maintains a table of o A router implementing the ARA option maintains a table of
link-layer associations for each of its OSPF areas. The ARA link-layer associations for each of its OSPF areas. The ARA
Association Table is used in calculating the ARA routing table Association Table is used in calculating the ARA routing table
extensions and in the inter-area ARA origination process. The extensions and in the inter-area ARA origination process. The
indexes for an entry in this table entry are the Vertex Type, indexes for an entry in this table are the Vertex Type, Vertex
Vertex ID and the Vertex Originator. The Vertex Type identifies ID and the Vertex Originator. The Vertex Type identifies the
the type of IP topology element that the link-layer information type of IP topology element that the link-layer information
is being associated with (i.e., a router or a network). The Ver- is being associated with (i.e., a router or a network). The Ver-
tex ID identifies a piece of a specific OSPF network's topology tex ID identifies a piece of a specific OSPF network's topology
(i.e., a router ID or an IP network number). The Vertex Origina- (i.e., a router ID or an IP network number). The Vertex Origina-
tor is the originator of the ARA's router ID. Entries in this tor is the originator of the ARA's router ID. Entries in this
table may be either active or non-active. Active entries are table may be either active or non-active. Active entries are
ones whose Logical Network IDs match one of the router's config- ones whose Logical Network IDs match one of the router's config-
ured (and currently active) Logical Network IDs. ured (and currently active) Logical Network IDs.
o Transit vertex data structures and the internal representation o Transit vertex data structures and the internal representation
of Type-3, Type-4 and Type-5 LSAs are extended to contain a of Type-3, Type-4 and Type-5 LSAs are extended to contain a
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o A router running the ARA option may be configured with a list o A router running the ARA option may be configured with a list
of logical network IDs. This list is used when the router calcu- of logical network IDs. This list is used when the router calcu-
lates the link-layer associations for its routing table and when lates the link-layer associations for its routing table and when
receiving ARAs to determine the change in active status for its receiving ARAs to determine the change in active status for its
ARA Association Table entries. Status information is kept for ARA Association Table entries. Status information is kept for
each of the router's attached logical network so that a router each of the router's attached logical network so that a router
can determine which logical networks are active at a given point can determine which logical networks are active at a given point
in time. To insure that ARA reachability is up-to-date, a change in time. To insure that ARA reachability is up-to-date, a change
in status of one of the router's connected logical networks must in status of one of the router's connected logical networks must
Coltun, Heinanen [Page 22]
result in the SPF calculation being rerun. result in the SPF calculation being rerun.
The absence of entries in the router's list of Logical Network The absence of entries in the router's list of Logical Network
IDs means that the router will only activate ARA Association IDs means that the router will only activate ARA Association
Table entries with the default Logical Network ID which is Logi- Table entries with the default Logical Network ID which is Logi-
cal Network ID 0. cal Network ID 0.
A router may originate ARAs with Logical Network IDs that are not A router may originate ARAs with Logical Network IDs that are not
contained in its list of Logical Network IDs. This may be used, contained in its list of Logical Network IDs. This may be used,
for example, to enable shortcuts to be set up from any router to for example, to enable shortcuts to be set up from any router to
any server but to disable shortcuts from being set up between any server but to disable shortcuts from being set up between
routers that are not associated with a server. routers that are not associated with a server.
12.0 Security Considerations
There are two types of issues that need be addressed when looking at
protecting routing protocols from misconfigurations and malicious
attacks. The first is authentication and certification of routing
protocol information. The second is denial of service attacks result-
ing from repetitive origination of the same router advertisement or
origination a large number of distinct advertisements resulting in
database overflow. Note that both of these concerns exist indepen-
dently of a router's support for the ARA option.
To address the authentication concerns, OSPF protocol exchanges may be
authenticated. OSPF supports multiple types of authentication; the
type of authentication in use can be configured on a per network seg-
ment basis. One of OSPF's authentication types, namely the Crypto-
graphic authentication option, is believed to be secure against pas-
sive attacks and provide significant protection against active
attacks. When using the Cryptographic authentication option, each
router appends a "message digest" to its transmitted OSPF packets.
Receivers then use the shared secret key and received digest to verify
that each received OSPF packet is authentic.
The quality of the security provided by the Cryptographic authentica-
tion option depends completely on the strength of the message digest
algorithm (MD5 is currently the only message digest algorithm speci-
fied), the strength of the key being used, and the correct implementa-
tion of the security mechanism in all communicating OSPF implementa-
tions. It also requires that all parties maintain the secrecy of the
shared secret key. None of the standard OSPF authentication types
provide confidentiality. Nor do they protect against traffic analysis.
For more information on the standard OSPF security mechanisms, see
Sections 8.1, 8.2, and Appendix D of [OSPF].
[DIGI] describes the extensions to OSPF required to add digital
signature authentication to Link State data and to provide a certifi-
cation mechanism for router data. [DIGI] also describes the added LSA
processing and key management as well as a method for migration from,
or co-existence with, standard OSPF V2.
Repetitive origination of advertisements are addressed by OSPF by man-
dating a limit on the frequency that new instances of any particular
LSA can be originated and accepted during the flooding procedure. The
frequency at which new LSA instances may be originated is set equal to
once every MinLSInterval seconds, whose value is 5 seconds (see Sec-
tion 12.4 of [OSPF]). The frequency at which new LSA instances are
accepted during flooding is once every MinLSArrival seconds, whose
value is set to 1 (see Section 13, Appendix B and G.5 of [OSPF]).
Proper operation of the OSPF protocol requires that all OSPF routers
maintain an identical copy of the OSPF link-state database. However,
when the size of the link-state database becomes very large, some
routers may be unable to keep the entire database due to resource
shortages; we term this "database overflow". When database overflow
is anticipated, the routers with limited resources can be accommodated
by configuring OSPF stub areas and NSSAs. [OVERFLOW] details a way of
gracefully handling unanticipated database overflows.
Appendix A: ARA Packet Formats Appendix A: ARA Packet Formats
This document defines four different types of Address Resolution This document defines four different types of Address Resolution
Advertisements. Each type of ARA begins with a standard 20-byte Opaque Advertisements. Each type of ARA begins with a standard 20-byte Opaque
LSA header [OPAQ]. This header is described in section A.1. Subsequent LSA header [OPAQ]. This header is described in section A.1. Subsequent
sections describe the specific advertisements and their content sections describe the specific advertisements and their content
including the formats of the resolution information. An ARA capable including the formats of the resolution information. An ARA capable
router may use the ARAs to build shortcut paths to other ARA capable router may use the ARAs to build shortcut paths to other ARA capable
routers. routers.
skipping to change at page 36, line ? skipping to change at page 28, line 4
ARAs. These ARAs advertise address resolution information for routers ARAs. These ARAs advertise address resolution information for routers
and networks within the local area and are advertised locally (they and networks within the local area and are advertised locally (they
have an area-local scope). have an area-local scope).
Area border routers may originate inter-area network and router ARAs. Area border routers may originate inter-area network and router ARAs.
These ARAs advertise address resolution to areas that are beyond the These ARAs advertise address resolution to areas that are beyond the
source local area. Inter-area network and router ARAs correspond to LS source local area. Inter-area network and router ARAs correspond to LS
Type-3 and LS Type-4 advertisements. Type-3 and LS Type-4 advertisements.
A.1 The ARA Header A.1 The ARA Header
All ARAs begin with a common 20-byte header. This header contains All ARAs begin with a common 20-byte header. This header contains
enough information to uniquely identify the ARA. The header, which is enough information to uniquely identify the ARA. The header, which is
a subset of the standard LSA header, includes the ARA Vertex Type and a subset of the standard LSA header, includes the ARA Vertex Type and
distribution scope. The Vertex Type is derived from the Opaque Type distribution scope. The Vertex Type is derived from the Opaque Type
field; the distribution scope is derived from the LS type field. ARAs field; the distribution scope is derived from the LS type field. ARAs
have an area-local scope (LS Type = 10). have an area-local scope (LS Type = 10).
The Vertex Identifier for an intra-area Router ARA is the advertising The Vertex Identifier for an intra-area Router ARA is the advertising
router field of the ARA header; for inter-area Router ARAs the vertex router field of the ARA header; for inter-area Router ARAs the vertex
Coltun, Heinanen [Page 23]
is identified by the advertising router field and the ASBR Router ID is identified by the advertising router field and the ASBR Router ID
field which is in the body of the advertisement. field which is in the body of the advertisement.
The Vertex Identifier for both intra and inter-area Network ARAs is The Vertex Identifier for both intra and inter-area Network ARAs is
contained in the network and mask field (which is in the body of the contained in the network and mask field (which is in the body of the
advertisement). A N-ARA may only identify a single network (i.e., advertisement). A N-ARA may only identify a single network (i.e.,
lists of networks are not permitted). lists of networks are not permitted).
ARAs make use of the P-bit in the same as the NSSA option [NSSA]. ARAs make use of the P-bit in the same as the NSSA option [NSSA].
That is, ARAs may not be advertised beyond area borders unless the P- That is, ARAs may not be advertised beyond area borders unless the P-
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| LS age | Options | LS Type | | LS age | Options | LS Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opaque Type | Opaque ID | | Opaque Type | Opaque ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router | | Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number | | LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length | | LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LS age LS age
The time in seconds since the ARA was originated. The time in seconds since the ARA was originated.
Options Options
The optional capabilities supported by the described portion The optional capabilities supported by the described portion
of the routing domain. The ARA uses two option bits. of the routing domain. The ARA uses two option bits.
O-bit O-bit
This bit describes the router's willingness to This bit describes the router's willingness to
Coltun, Heinanen [Page 24]
receive and forward Opaque-LSAs as specified in receive and forward Opaque-LSAs as specified in
[OPAQ]. All routers supporting the ARA option as [OPAQ]. All routers supporting the ARA option as
described in this document support the Opaque described in this document support the Opaque
option. option.
P-Bit P-Bit
ARAs make use of the P-Bit in a manner consistent ARAs make use of the P-Bit in a manner consistent
with [NSSA]. An ARA may not be advertised beyond with [NSSA]. An ARA may not be advertised beyond
an area border unless the P-bit is set in the ori- an area border unless the P-bit is set in the ori-
ginal intra-area ARA. ginal intra-area ARA.
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tions for the advertising router. These ARAs are advertised tions for the advertising router. These ARAs are advertised
throughout the local area. throughout the local area.
Opaque Type-2 advertisements are intra-area Network Address Opaque Type-2 advertisements are intra-area Network Address
Resolution Advertisements and contain link-layer associa- Resolution Advertisements and contain link-layer associa-
tions for a router's directly connected IP networks (or tions for a router's directly connected IP networks (or
hosts). These ARAs are advertised throughout the local hosts). These ARAs are advertised throughout the local
area. area.
Opaque Type-3 advertisements are inter-area Network Address Opaque Type-3 advertisements are inter-area Network Address
Resolution Advertisements and contain link-layer associa- Resolution Advertisements and contain link-layer
tions for IP networks that reside in other areas. Inter- associations for IP networks that reside in other areas.
area N-ARAs are coordinated with inter-area network (LS Inter-area N-ARAs are coordinated with inter-area network
Type-3) advertisements. (LS Type-3) advertisements.
Opaque-type 4 advertisement are inter-area Router Address Opaque-type 4 advertisement are inter-area Router Address
Resolution Advertisements and contain link-layer associa- Resolution Advertisements and contain link-layer associa-
tions for ASBR that reside in other areas. Inter-area R- tions for ASBR that reside in other areas. Inter-area R-
ARAs are coordinated with inter-area ASBR (LS Type-4) adver- ARAs are coordinated with inter-area ASBR (LS Type-4) adver-
tisements. tisements.
Coltun, Heinanen [Page 25]
Opaque ID Opaque ID
A 24-bit semantic-less LSA identifier which serves to dif- A 24-bit semantic-less LSA identifier which serves to dif-
ferentiate between multiple LSAs originated by the same ferentiate between multiple LSAs originated by the same
router. The Opaque ID must be unique for an advertising router. The Opaque ID must be unique for an advertising
router within the advertising scope of the LSA. router within the advertising scope of the LSA.
Advertising Router Advertising Router
The Router ID of the router that originated the ARA. For The Router ID of the router that originated the ARA. For
intra-area R-ARAs the Advertising Router also serves as the intra-area R-ARAs the Advertising Router also serves as the
ARA Vertex Identifier. ARA Vertex Identifier.
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an inter-area R-ARA), the R-ARA must have the P-bit set in its Options an inter-area R-ARA), the R-ARA must have the P-bit set in its Options
field. field.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 10 | | LS age | Options | 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | Opaque ID | | 1 | Opaque ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Coltun, Heinanen [Page 26]
| Advertising Router | | Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number | | LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length | | LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+ Vertex Association +-+ +-+ Vertex Association +-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 36, line ? skipping to change at page 32, line 11
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 10 | | LS age | Options | 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | Opaque ID | | 2 | Opaque ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router | | Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number | | LS Sequence Number |
Coltun, Heinanen [Page 27]
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | Length | | LS checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Network Number | | IP Network Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Network Mask | | IP Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+ Vertex Association +-+ +-+ Vertex Association +-+
| | | |
skipping to change at page 36, line ? skipping to change at page 32, line 45
ing on a single IP network/subnet/supernet. ing on a single IP network/subnet/supernet.
The body of the N-ARA consists of a list of associations for this IP The body of the N-ARA consists of a list of associations for this IP
Network Number. Each Vertex Association begins with a common 6-byte Network Number. Each Vertex Association begins with a common 6-byte
header (described in Section A.6) followed by association-specific header (described in Section A.6) followed by association-specific
resolution information (described in Section A.7). resolution information (described in Section A.7).
A.4 Inter-Area Network ARAs A.4 Inter-Area Network ARAs
Opaque Type-3 advertisements are inter-area Network Address Resolution Opaque Type-3 advertisements are inter-area Network Address Resolution
Advertisements and contain associations for a remote area's IP net- Advertisements and contain associations for a remote area's IP
works (or hosts). Inter-area N-ARAs are coordinated with LS type-3 networks (or hosts). Inter-area N-ARAs are coordinated with LS type-3
advertisements. advertisements.
Inter-area network ARAs are originated by an area border router into a Inter-area network ARAs are originated by an area border router into a
target area if 1) the ABR originates a type-3 LSA for the network into target area if 1) the ABR originates a type-3 LSA for the network into
the target area, 2) the network is not included in any of the area the target area, 2) the network is not included in any of the area
border router's configured area ranges, 3) there is an N-ARA for the border router's configured area ranges, 3) there is an N-ARA for the
Coltun, Heinanen [Page 28]
network in the source area and 4) the source N-ARA is an intra-area network in the source area and 4) the source N-ARA is an intra-area
N-ARA with a P-bit set in the options field (which denotes that the N-ARA with a P-bit set in the options field (which denotes that the
originator of the N-ARA will allow the N-ARA to be propagated into originator of the N-ARA will allow the N-ARA to be propagated into
other areas) or the source N-ARA is an inter-area N-ARA. other areas) or the source N-ARA is an inter-area N-ARA.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 10 | | LS age | Options | 10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 36, line ? skipping to change at page 34, line 11
IP Network Number IP Network Number
One of the router's directly connect network. This number One of the router's directly connect network. This number
represents an IP network/subnet/supernet. represents an IP network/subnet/supernet.
IP Network Mask IP Network Mask
A 32-bit number indicating the range of IP addresses resid- A 32-bit number indicating the range of IP addresses resid-
ing on a single IP network/subnet/supernet. ing on a single IP network/subnet/supernet.
The body of the N-ARA consists of a list of associations for this IP The body of the N-ARA consists of a list of associations for this IP
Coltun, Heinanen [Page 29]
Network Number. Each Vertex Association begins with a common 6-byte Network Number. Each Vertex Association begins with a common 6-byte
header (described in Section A.6) followed by association-specific header (described in Section A.6) followed by association-specific
resolution information (described in Section A.7). resolution information (described in Section A.7).
A.5 Inter-Area Router ARAs A.5 Inter-Area Router ARAs
Opaque Type-4 advertisements are inter-area Router Address Resolution Opaque Type-4 advertisements are inter-area Router Address Resolution
Advertisements and contain associations for the an autonomous system Advertisements and contain associations for the an autonomous system
boundary router. Inter-area R-ARAs are coordinated with LS type-4 boundary router. Inter-area R-ARAs are coordinated with LS type-4
advertisements. advertisements.
skipping to change at page 36, line ? skipping to change at page 35, line 11
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+ Vertex Association +-+ +-+ Vertex Association +-+
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+-+ Vertex Association +-+ +-+ Vertex Association +-+
| | | |
Coltun, Heinanen [Page 30]
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
ASBR Router ID ASBR Router ID
The router ID of the ASBR being advertised. This field The router ID of the ASBR being advertised. This field
corresponds to the link-state ID of the LS type-4 advertise- corresponds to the link-state ID of the LS type-4 advertise-
ment. ment.
The body of the inter-area R-ARA consists of a list of associations The body of the inter-area R-ARA consists of a list of associations
for the advertising router. Each Vertex Association begins with a for the advertising router. Each Vertex Association begins with a
common 6-byte header (described in Section A.6) followed by common 6-byte header (described in Section A.6) followed by
skipping to change at page 36, line ? skipping to change at page 36, line 4
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Svc Type | IS Svc Name | Admin Weight | Assoc Length + | Link Svc Type | IS Svc Name | Admin Weight | Assoc Length +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Logical Network ID | Resolution Information + | Logical Network ID | Resolution Information +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ Remaining Octets of Resolution Information padded to 32-bits + + Remaining Octets of Resolution Information padded to 32-bits +
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link Svc Type Link Svc Type
Identifies the link-layer functionality for this associa- Identifies the link-layer functionality for this associa-
tion. Link Service Types 1, 2 and 3 are defined by this tion. Link Service Types 1, 2 and 3 are defined by this
specification. All other Link Service Types are reserved specification. All other Link Service Types are reserved
Coltun, Heinanen [Page 31]
for definition by the IANA (iana@isi.edu). The current list for definition by the IANA (iana@isi.edu). The current list
of Link Service Types is described below in Table 1. of Link Service Types is described below in Table 1.
Link Service Type Description Link Service Type Description
------------------------------------------------- -------------------------------------------------
1 ATM Point-To-Point 1 ATM Point-To-Point
2 ATM MultiPoint-To-Point 2 ATM MultiPoint-To-Point
3 ATM Point-To-MultiPoint 3 ATM Point-To-MultiPoint
Table 1 Table 1
skipping to change at page 36, line ? skipping to change at page 37, line 8
specific logical network identified in the resolution infor- specific logical network identified in the resolution infor-
mation. An ARA capable router is configured with a list of mation. An ARA capable router is configured with a list of
Logical Network IDs. The default value (i.e., only one Logical Network IDs. The default value (i.e., only one
overlay network or too lazy to care) for the ID is 0. overlay network or too lazy to care) for the ID is 0.
Resolution Information Resolution Information
The resolution information field includes link-layer and The resolution information field includes link-layer and
service-type specific information. The contents of this service-type specific information. The contents of this
field is defined in section A.7 of this document. The Ver- field is defined in section A.7 of this document. The Ver-
tex Association may include several resolution information tex Association may include several resolution information
Coltun, Heinanen [Page 32]
items. items.
A.7 Resolution Information A.7 Resolution Information
The resolution information field is an extensible field that includes The resolution information field is an extensible field that includes
link-layer and service-type specific information. link-layer and service-type specific information.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res Type | Res Length | Resolution Value | | Res Type | Res Length | Resolution Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 36, line ? skipping to change at page 38, line 8
2 ATM LIJ Call Identification 2 ATM LIJ Call Identification
Table 2 Table 2
Res Length Res Length
The total length in octets of this resolution information The total length in octets of this resolution information
field This value includes the Res Type and Res Length field This value includes the Res Type and Res Length
fields. fields.
Resolution Value Resolution Value
Coltun, Heinanen [Page 33]
The resolution type-specific data. The resolution type-specific data.
A.7.1 ATM Address A.7.1 ATM Address
An ATM address is the Resolution Type 1. This includes the type and An ATM address is the Resolution Type 1. This includes the type and
length of ATM number (8 bits), the type and length of ATM subaddress length of ATM number (8 bits), the type and length of ATM subaddress
(8 bits), the ATM number (x octets) and possibly the ATM subaddress (y (8 bits), the ATM number (x octets) and possibly the ATM subaddress (y
octets). octets).
8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1
skipping to change at page 36, line ? skipping to change at page 39, line 9
Bit(s) Description Bit(s) Description
------------------------------------------------- -------------------------------------------------
8 Reserved = 0 (for future use) 8 Reserved = 0 (for future use)
7 Type = 0 ATM Forum NSAPA format 7 Type = 0 ATM Forum NSAPA format
= 1 E.164 format = 1 E.164 format
6-1 Length = 6 bit unsigned octet length of 6-1 Length = 6 bit unsigned octet length of
address (MSB = bit.6, LSB = bit.1). address (MSB = bit.6, LSB = bit.1).
Value range is from 0 to 20 (decimal). Value range is from 0 to 20 (decimal).
Coltun, Heinanen [Page 34]
A non-existing ATM subaddress is indicated by setting the subaddress A non-existing ATM subaddress is indicated by setting the subaddress
length to zero. If the subaddress length is zero, the corresponding length to zero. If the subaddress length is zero, the corresponding
type field MUST be ignored and the ATM subaddress field MUST NOT con- type field MUST be ignored and the ATM subaddress field MUST NOT con-
sume any octets in the packet. sume any octets in the packet.
The ATM number and ATM subaddress fields are encoded as defined by the The ATM number and ATM subaddress fields are encoded as defined by the
ATM Forum UNI 3.1 [AF1] signalling specification. ATM Forum UNI 3.1 [AF1] signalling specification.
A.7.2 ATM LIJ Call Identification A.7.2 ATM LIJ Call Identification
skipping to change at page 36, line ? skipping to change at page 40, line 9
Format Of LIJ Call Identification Format Of LIJ Call Identification
The Leaf Initiated Join Call Identifier Value is encoded as defined in The Leaf Initiated Join Call Identifier Value is encoded as defined in
Section 6.1.2.1 of the ATM Forum UNI 4.0 [AF2] signalling specifica- Section 6.1.2.1 of the ATM Forum UNI 4.0 [AF2] signalling specifica-
tion. tion.
References References
[AF1] ATM Forum, "ATM User-Network Interface (UNI) Specification [AF1] ATM Forum, "ATM User-Network Interface (UNI) Specification
Version 3.1.", ISBN 0-13-393828-X, Prentice-Hall, Inc., Upper Version 3.1.", ISBN 0-13-393828-X, Prentice-Hall, Inc., Upper
Coltun, Heinanen [Page 35]
Saddle River, NJ, 07458, September, 1994. Saddle River, NJ, 07458, September, 1994.
[AF2] ATM Forum, "ATM User-Network Interface (UNI) Signalling [AF2] ATM Forum, "ATM User-Network Interface (UNI) Signalling
Specification", July 1996. Specification", July 1996.
[DIGI] S. Murphy, M. Badger, B. Wellington, "OSPF with Digital
Signatures", RFC 2154, Trusted Information Systems, June 1997.
[HEIN] Heinanen, J., "Intra-area IP unicast among routers over legacy ATM", [HEIN] Heinanen, J., "Intra-area IP unicast among routers over legacy ATM",
Internet Draft, July 1997, <draft-ietf-ion-intra-area-unicast-00.txt> Internet Draft, July 1997, <draft-ietf-ion-intra-area-unicast-00.txt>
[IS] S. Shenker and J. Wroclawski. "Network Element QoS Control [IS] S. Shenker and J. Wroclawski. "Network Element QoS Control
Service Specification Template". Internet Draft, July 1996, <draft- Service Specification Template". Internet Draft, July 1996, <draft-
ietf-intserv-svc-template-03.txt> ietf-intserv-svc-template-03.txt>
[OPAQ] Coltun, R., "The OSPF Opaque LSA Option", Internet Draft
May 1997, <draft-ietf-ospf-opaque-01.txt>
[OSPF] Moy, J., "OSPF Version 2", RFC 2178, July 1997
[NHRP] Luciani, J., Katz, D., Piscitello, D., Cole, B., "NBMA [NHRP] Luciani, J., Katz, D., Piscitello, D., Cole, B., "NBMA
Next-Hop Resolution Protocol", Internet Draft, March 1997, Next-Hop Resolution Protocol", Internet Draft, March 1997,
<draft-ietf-rolc-nhrp-11.txt> <draft-ietf-rolc-nhrp-15.txt>
[NSSA] Coltun, R. and V. Fuller, "The OSPF NSSA Option", RFC 1587, [NSSA] Coltun, R. and V. Fuller, "The OSPF NSSA Option", RFC 1587,
RainbowBridge Communications, Stanford University, March 1994. RainbowBridge Communications, Stanford University, March 1994.
[OPAQ] Coltun, R., "The OSPF Opaque LSA Option", Internet Draft
May 1997, <draft-ietf-ospf-opaque-04.txt>
[OSPF] Moy, J., "OSPF Version 2", RFC 2178, July 1997
[OVERFLOW] Moy, J., "OSPF Database Overflow", RFC 1765,
Cascade, March 1995.
 End of changes. 

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