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Versions: 00

Network Working Group                             Robert Raszuk (Editor)
Internet Draft                                           Chandra Appanna
Category: Standards Track                             Cisco Systems, Inc
Expires: December 2003                               Pedro Roque Marques
                                                   Juniper Networks, Inc
                                                               June 2003
                             IBGP Auto Mesh
                 draft-raszuk-idr-ibgp-auto-mesh-00.txt


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet Drafts are working documents of the Internet Engineering
   Task Force (IETF), its Areas, and its Working Groups. Note that other
   groups may also distribute working documents as Internet Drafts.

   Internet Drafts are draft documents valid for a maximum of six
   months.  Internet Drafts may be updated, replaced, or obsolete by
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   draft" or "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


Abstract

   The distribution of BGP routing information within an autonomous
   system requires all border routers to be fully meshed. This
   constitutes a significant operational problem in terms of
   configuration management.

   This has led to the wide-spread adoption of route reflection
   [RFC2796], primarily in order to reduce the number systems which
   configuration must be modified in order to introduce or remove a new
   internal BGP speaker. Route reflection, however, implies with it
   information reduction which is not always desired.

   This document defines a discovery mechanism that is designed to
   address the problem of introducing (or removing) a BGP speaker into
   an iBGP mesh without implying any other behavior change when compared



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   to manual configuration.


1. Specification of Requirements

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].


2. Introduction

   One of the most common complains received from operators is the
   comment on complexities associated with configuration of BGP meshes.

   This draft attempts to make this claim a history by proposing auto
   discovery of internal BGP peers via configuration information
   flooding as well as a set of procedures which would allow to
   establish IBGP sessions automatically.

   It should be noted that for easy and fast deployment flooding of
   information is piggybacked on top of existing IGP mechanisms. This
   feature is designed with flooding mechanism transparency in mind.
   When new and more effective flooding protocol is introduced and
   deployed into production networks it should be with no additional
   effort on the BGP component to migrate the flooding from IGPs to such
   a new protocol.

   Unlike other attempts in this area it does not relay on any
   management station. Also it keeps all BGP functional and transport
   mechanism unchanged.

   The particular piece of functionality this draft addresses is
   distribution of related local configuration to all routers within
   flooding scope as well as usage of this information in establishment
   of IBGP peering.

   Today we can observe a number of network topologies where IBGP is
   being used to distribute routing information between BGP speakers:

   A - Full iBGP mesh between all routers in the AS
   B - Full iBGP mesh between all members of confederation
   C - Route reflectors clusters peering
   D - Full iBGP mesh between all PEs/ASBRs and BGP free core

   In the operation section we will describe how this draft can automate
   IBGP peering in all of the above scenarios.




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   Another very important observation is that today BGP often play other
   roles than just distribution of IPv4 reachability information. With
   introduction of multiprotocol BGP extensions [RFC2858] BGP speakers
   may be configured to keep and maintain data belonging to multiple
   address families.

   In multiprotocol environments, the IBGP mesh for one address family
   may not match the mesh for a different address family as in the case
   where different route reflectors are used for different applications.
   This draft will also automate IBGP session establishment with
   matching AFIs taken into consideration of the auto discovered peers.

   Historically introduction of route reflection drastically removed the
   need for full mesh manual configuration of all BGP speakers in a
   domain. It also reduced the number of TCP session each BGP speakers
   needed to handle.

   Another characteristics of route reflection is their ability to
   eliminate number of advertised paths to a given peer to only best
   path from reflector's point of view.

   While this last point was originally thought of a benefit (at least
   from the perspective of best effort ipv4 reachability) today's
   applications require a bit more granular path's classification and
   features like IBGP multipath is becoming already a production
   requirement. To keep the former benefit of reduced configuration or
   low number of TCP sessions approaches like add-paths draft [ADD-PATH]
   are being currently under investigation.

   It should be noticed that idea presented in this draft eliminates any
   manual configuration for full mesh BGP peering. Also modern operating
   systems implementations can hold and maintain much more TCP sessions
   that their predecessors could. Therefore by auto meshing all or
   selected address families on BGP speakers the need for route
   reflection becomes obsolete in some cases.

   In order to reduce amount of information distributed across IBGP
   sessions to only a required subset outbound route filtering
   techniques could be employed [IDR-ORF].

   Another operational benefit of using IBGP auto mesh is the ease of AS
   renumbering or merges/migrations. It is generally very difficult to
   manually change the AS number on all BGP speakers in a short
   maintenance window. With the automation such task would be much
   easier to accomplish.






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3. The BGP Auto Discovery TLV

   This section proposes an encoding to be used in IPv4 & IPv6 networks.

   The BGP Auto Discovery TLV is defined as follows:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TLV Type    |    Length     |     FLOODING RESERVED     |F|D|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        BGP Identifier                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  FRAG |     BGP  RESERVED     |        16 bit CHECKSUM        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Autonomous System(s) or confederation sub-AS(s) sub-TLV    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             IPv4/IPv6  Peering Address sub-TLV                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             AFI/SAFI for mesh topologies sub-TLV              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          AFI/SAFI for reflection topologies sub-TLV           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Old BGP Identifier sub-TLV (opt)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 1. BGP Auto Discovery TLV

3.1. TLV Type

   BGP Auto Discovery TLV is proposed to be carried in OSPF Router
   Information LSA [LINDEM1] with area scope or domain wide scope
   depending on the configuration. Details describing OSPF specifics and
   encoding will be described in [OSPF-BGP].

   In ISIS BGP Auto Discovery TLV is proposed to be carried as a new TLV
   with flooding scope local to the intra area or domain wide. Details
   describing ISIS specific encoding will be described in [ISIS-BGP].

   The selection of ISIS and OSPF for flooding is mostly based on the
   fact that those protocols already have a flooding mechanism which can
   be reused for the purpose of required in this proposal information
   distribution.

   It is a strong design goal that flooding of BGP Auto Discovery TLV
   can be realized over any other protocol when such is deployed and
   when it can provide further benefits. For example: selective groups
   of destinations or disjoined information distribution trees per



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   AFI/SAFI.

   In cases of multiple bgp processes running on a router each BGP
   process should send it's own BGP Auto Discovery TLV with a different
   BGP Identifier.

3.2. TLV Length

   Length  - Total length in octets of this TLV

   The minimum TLV length can be 10 octets.

   When a size of the TLV reaches 255 octets TLV fragmentation needs to
   occur. A special "FRAG" 4 bit counter has been allocated in the BGP
   Control Information's first octet for unlikely cases where BGP Auto
   Discovery TLV needs to be splitted across multiple TLVs for a given
   BGP speaker.

   It is estimated that the average size of BGP Auto Discovery TLV in
   today's production environments will be anywhere from 30-50 octets.

3.3. Global flooding flags

   This comprises of one or more global for given BGP Auto Discovery TLV
   flags related to flooding. Currently defined are the following flags:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   TLV Type    |    Length     |     FLOODING RESERVED     |F|D|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 2. Value field of global flags

   Symbol          Definition

   F               Flooding scope
   D               Down Bit

   "F" {flooding} flooding scope of this TLV. When set domain wide
       flooding scope is required, when not set TLV should not be
       flooded into other areas or levels. Default not set
       indicating area/level wide flooding only.

   "D" {down} down bit set by ISIS when leaked to other areas/levels.

   When advertised BGP Auto Discovery TLV for a given BGP Identifier
   does not contain any sub-TLVs it should be interpreted as an implicit



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   withdraw of any previously advertised BGP Auto Discovery TLV for a
   given BGP Identifier.

   This is intentional not to duplicate BGP capabilities in this
   message. BGP operation in session establishment to auto discovered
   peers should remain without any changes as compared to today's
   operation.

   All reserved flags and not defined yet should be set to zeros.

3.4. BGP Identifier

   4 octet value set to BGP ID [IDR-BGP4]. When BGP ID is being changed
   on a BGP speaker next BGP Auto Discovery TLV announced should contain
   "Old BGP ID sub-TLV". Presence of this sub-TLV is an indication that
   the received BGP Auto Discovery TLV is being related to previously
   flooded BGP information with the contained in this sub-TLV BGP
   Identifier.

3.5. BGP Control Information

   The below 4 octets with BGP specific control information has been
   defined:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  FRAG |     BGP  RESERVED     |        16 bit CHECKSUM        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 3 BGP Control Information

3.6. Fragmentation counter

   When a size of the BGP Auto Discovery TLV reaches 255 octets TLV
   fragmentation needs to occur. A special "FRAG" 4 bit counter has been
   allocated for unlikely cases where BGP Auto Discovery TLV needs to be
   splitted across multiple TLVs for a given BGP speaker.

3.7. Checksum

   Depending on the flooding protocol being utilized BGP may be
   receiving identical information periodically. To allow easy
   determination if the content of the TLV has changed for a given BGP
   Identifier 16 bit checksum has been defined. Checksum should be
   computed from the content of the entire BGP Auto Discovery TLV
   (before potential fragmentation) excluding first 4 octets of the TLV.




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4. The BGP Auto Discovery sub-TLVs

   In following subsections we will focus on describing each of the
   sub-TLVs directly related to BGP operation. The format of each sub-
   TLV will be following:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |            RESERVED           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Value(s)...                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 4. BGP Sub-TLV

4.1. BGP Autonomous System(s) sub-TLV

   Type        One octet field set to value of 1.
   Length      One octet field that indicates the length of the value
               portion in octets.
   Reserved    Two octet field reserved for flags and sub-TLV control
   Value       4 octet BGP Autonomous System Number(s) [IDR-BGP4]
               [IDR-AS4] or confederation sub-AS [RFC1965].

   Advertising multiple autonomous system numbers may be required during
   AS renumbering and merges with other ASes. Therefore this proposal
   does not limit advertisement to a single AS value per BGP speaker.

   The peering attempt should be made only to those peers which match
   locally configured AS number or numbers (multi-as migration case).

   When confederation is used sub-AS will limit the scope of full mesh
   peering only to a given sub-AS even if flooding scope is common to
   all sub-ASes. Usage of route reflectors within each confederation
   sub-AS is also supported.

4.2. IPv4 Peering Address sub-TLV

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |           RESERVED          |F|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      IPv4 Peering Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 5. BGP IPv4 Peering Sub-TLV



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   Type        One octet field set to value of 2.
   Length      One octet field that indicates the length of the value
               portion in octets.
   Reserved    Set to all zeros
   Flag        "F"   - Force new peering. Default not set.
   Value       4 octet ipv4 peering address

   This address will be used by BGP speakers as a destination in BGP
   Open message. Sending a BGP Auto Discovery TLV with new peering
   address is an explicit withdraw of the previously advertised one.

   When such a messages is received old peering should remain intact
   when "F" flag is not set (default). When session is cleared manually
   or IGP reachability to the old peering address disappears new peering
   address should be used.

   When "F" flag is set new peering address should be used immediately
   and current BGP session to the peer restarted.

4.3. IPv6 Peering Address sub-TLV

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |            RESERVED         |F|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                      IPv6 Peering Address                     |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 6. BGP IPv6 Peering Sub-TLV

   Type        One octet field set to value of 3.
   Length      One octet field that indicates the length of the value
               portion in octets.
   Reserved    Set to all zeros
   Flag        "F"   - Force new peering. Default not set.
   Value       16 octet ipv6 peering address

   This address will be used by BGP speakers as the destination in BGP
   Open message. Sending a BGP Auto Discovery TLV with new peering
   address is an explicit withdraw of the previously advertised one.

   When such a messages is received old peering should remain intact
   when "F" flag is not set (default). When session is cleared manually
   or IGP reachability to the old peering address disappears new peering



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   address should be used.

   When "F" flag is set new peering address should be used immediately
   and current BGP session to the peer restarted.

   When both IPv4 & IPv6 peering addresses are present it is up to the
   implementation to decide on the peering address selection.

4.4. AFI/SAFI for mesh topologies sub-TLV

   Type        One octet field set to value of 4.
   Length      One octet field that indicates the length of the value
               portion in octets.
   Reserved    Set to zero
   Value       2 octet Address Family Identifier(s) [RFC2858]
               1 octet Subsequent Address Family Identifier [RFC2858]
               1 octet Per AFI/SAFI Flags

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |            RESERVED           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Address Family Identifier 1 |     SAFI 1    |   RESERVED  |O|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                .....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Address Family Identifier 1 |     SAFI 2    |   RESERVED  |O|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 7. Value field of BGP AFI/SAFI mesh topologies sub-TLV

   Sub-TLV Value Flags:

   "O"  - Originator or EBGP speaker

   Originator flag:

   IBGP sessions in a full or partial mesh topology are required to
   directly peer with those BGP speakers which originate routes or which
   maintain EBGP sessions. This flag should be used to mark such a bgp
   speakers when advertising BGP Auto Discovery TLV. On reception this
   flag should be used for selection or required IBGP peering
   candidates.

   It is important to note that the actual state of EBGP session or
   present or not in the routing table of redistribuited prefix is not
   relevant and this bit should be set always when EBGP session or local



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   route origination is configured.

4.5. AFI/SAFI for reflection topologies sub-TLV

   Type        One octet field set to value of 5.
   Length      One octet field that indicates the length of the value
               portion in octets.
   Reserved    Set to zero
   Value       2 octet Address Family Identifier(s) [RFC2858]
               1 octet Subsequent Address Family Identifier [RFC2858]
               1 octet Per AFI/SAFI Flags

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |            RESERVED           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Address Family Identifier N |     SAFI N    |  RESERVED |R|O|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Cluster ID  N                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                 ......
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Address Family Identifier X |     SAFI X    |  RESERVED |R|O|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Cluster ID X                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 8. Value field of AFI/SAFI reflection sub-TLV

   Sub-TLV Value Flags:

   "O"  - Originator or EBGP speaker
   "R"  - Route Reflector for given AFI-SAFI/Cluster_ID combination

   See section "AFI/SAFI for mesh topologies sub-TLV" for explanation of
   "O" flag.

   "R"  - Route reflector flag.

   When "R" flag is set BGP speaker announcing this TLV is configured
   for route reflection function for a given AFI/SAFI combination. In
   addition when "R" bit is set the following cluster ID 4 octet value
   [RFC2796] indicates cluster id assigned for a given reflection
   function.

   Clients of route reflection will send their cluster ID lists assigned
   to each AFI/SAFI without "R" bit set. When client wishes to indicate



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   the request to become a member of all possible cluster_ids for given
   AFI/SAFI combination within a flooding scope of his BGP Auto
   Discovery TLV the "R" bit should not be set and the value of
   cluster_id associated with the AFI/SAFI should be set to all zeros.

   To allow chain of route reflection (hierarchy) it is perfectly valid
   for a BGP speaker to have for a given AFI/SAFI a "R" bit set for one
   cluster IDs (ie to perform a route reflection function) and in the
   same time for other cluster ID values be a client of other route
   reflectors (R bit not set).

   Network designs of reflection within confederations are also
   supported.

   At this time of publication authors will also leave the implementor's
   freedom to allow single sided signaling only from route reflectors to
   the clients. When client receives the BGP Auto Discovery TLV which
   contains the interesting cluster ID and has R bit set it can initiate
   BGP Open without injecting any information about his own BGP
   configuration in the reflection topologies into the network.

4.6. Old BGP Identifier sub-TLV

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |    Length     |            RESERVED           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Old BGP Identifier                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 9. Old BGP Identifier Sub-TLV

   Type        One octet field set to value of 6.
   Length      One octet field that indicates the length of the value
               portion in octets.
   Reserved    Set to all zeros
   Value       4 octet BGP Identifier [IDR-BGP4].

   When BGP Identifier is being replaced with a new value the "Old BGP
   Identifier" sub-TLV must be present and contain a previously
   advertised BGP ID for this given BGP speaker.









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5. Operation

   Each BGP speaker configured to participate in an IBGP auto mesh
   should pass to flooding component BGP Auto Discovery TLV with it's
   own local configuration dependent information.

   On the receive side, a cache should be maintained by BGP with all
   received information from flooding component about other BGP speakers
   announcing their BGP Auto Discovery TLVs in a given area or domain.

   IBGP auto mesh configuration should allow for per address family and
   subsequent address family disjoint topologies granularity.

   When multiple AFI/SAFI pairs match on any two BGP speakers only one
   IBGP session should be attempted. Regular BGP capabilities will be
   used to negotiate given AFI/SAFI mutual set. Never less AFI/SAFI
   granularity is required to allow for very fine grade disjoint
   topologies for different types of distributed by BGP information.

5.1. Full mesh topologies

   When operator finds required to fully or partially mesh BGP speakers
   "AFI/SAFI for mesh topologies" sub-TLV should be utilized.

   BGP speakers may be eligible for origination of routes or may be
   configured for EBGP peering. We will call them "O" flag eligible (see
   section "AFI/SAFI for mesh topologies sub-TLV").

   BGP speakers "O" flag eligible may establish session with any other
   BGP speaker if passing all peering criteria for a given AFI/SAFI.

   BGP speakers "O" flag not eligible (ex: P routers) should not
   establish IBGP peering to any other "O" flag not eligible BGP
   speakers.

   One possible example of such a configuration could be vpnv4 AF
   connecting all PEs in a domain into a full IBGP mesh.

   After reception of peers BGP Auto Discovery TLV BGP speaker should
   check for autonomous system numbers match as well as AFI/SAFI
   identifiers match. Positive results from the above actions should
   trigger a standard process of connection establishment attempt with
   the peer.

   It is also highly recommened that a local range of allowed peering
   addressed be also maintained and consulted at each attempt to
   establish a new IBGP peering.




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   BGP Auto Discovery TLV may be area/level or domain wide in full mesh
   topologies. The default should be area/level wide flooding.

5.2. Confederations

   To automate iBGP full mesh establishment in each confederation sub-AS
   each confederation member should advertise it's confederation sub-AS
   instead of main AS (confederation_id) it is a member of in BGP
   Autonomous System(s) sub-TLV.

   There could be two cases here:

   A) Confederation sub-ASes strictly contained within flooding scope
   B) Confederation sub-ASes unrelated to flooding topology

   Case (A) BGP auto discovery TLV flooding scope should be limited to
   one area/level.

   Case (B) BGP auto discovery TLV flooding scope should be domain wide
   and use of Auto Peering Range(s) sub-TLV is highly recommended.

   In the cases where reflectors are used within each confederation
   rather then direct peering "AFI/SAFI for reflection topologies sub-
   TLV" should be used instead of "AFI/SAFI for mesh topologies sub-
   TLV".

5.3. Route Reflectors

   When operator wishes to automate establishment of BGP sessions to
   route reflectors the only additional information required is
   configuration of at least one identical cluster id on both route
   reflector as well as on route reflector client. As mentioned earlier
   even this requirement could be relaxed by implementation supporting
   single sided signaling of reflector capabilities. The drawback in
   such a case is that route reflector injecting his BGP Auto Discovery
   TLV would also need to be configured with an additional information
   allowing to distinguish BGP Open requests coming from clients as well
   as those coming from non clients based on the peering address range
   and mark such a peering accordingly.

   Routers or devices designated to serve route reflector function shall
   advertise their "AFI/SAFI for reflection topologies" sub-TLV with "R"
   flag set as well as with their cluster id(s) attached.

   If IBGP session will be established between route reflector ("R" flag
   set) and non route reflector BGP speaker ("R" flag not set) who's
   specific AFI/SAFI cluster ID matches on at least one entry with given
   route reflector cluster id it should be marked as route reflector



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   client.

   BGP speakers which are not to act as route reflectors ("R" flag not
   set) and do not have configured cluster id value(s) indicating their
   designation as route reflector clients would attempt to establish
   regular IBGP peering to other BGP speakers in the domain (per rules
   described in section "Full mesh topologies").

   An implementation may also allow the additional route reflection
   client to client full mesh. This is left for the implementor's choice
   to be enabled with a configuration option.

   Route reflection chaining (reflector hierarchy) is fully supported.
   Route reflector server may advertise for a given AFI/SAFI his ability
   to reflect routes for one set of cluster ID(s) ("R" bit set) and in
   the same time for the same AFI/SAFI value submit a list of cluster
   IDs without "R" bit set indicating the willingness to become a
   regular client on servers eligible to reflect those cluster ID(s).

   When client wishes to indicate the request to become a member of all
   possible cluster_ids for given AFI/SAFI combination within a flooding
   scope of his BGP Auto Discovery TLV the "R" bit should not be set and
   the value of cluster_id associated with the AFI/SAFI should be set to
   all zeros.


6. Local peering verification

   It is highly recommended for an implementation to support local
   configuration of all possible remote peering address ranges expected
   to be received via BGP Auto Discovery TLV messages.

   In particular this can protect from configuration mistakes when
   peering in a full or partial mesh and setting flooding scope
   accidentally to domain wide.

   In this version of the draft the decision has been made not to flood
   this local peering range list to the remote peers. Such a flooding
   could further protect from even sending BGP Open message when given
   bgp speaker own peering address does not match received list from a
   peer.

   That decision can be revisited in the future versions of this work
   and new sub-TLV for flooding this information can be added.







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7. Deployment Considerations

   The idea described in this document should not present any deployment
   challenges. It is expected that all implementations would still allow
   manual neighbor establishments which in fact could be complimentary
   and co-existing to the IBGP auto mesh.

   In addition BGP Auto Discovery TLV exchange could be enabled just for
   informational purposes while provisioning would remain manual before
   operational teams get familiar with new functionality.

   Incremental deployment with enabling just a few routers to advertise
   BGP Auto Discovery TLV while maintaining manual configuration based
   peering with the rest of the network is supported. An implementation
   may also allow for mixed peering for example reflector client being
   configured automatically while reflector's clusters itself being
   interconnected manually.


8. IANA Considerations

   There are no IANA considerations required in this document.
   Extensions to ISIS [ISIS-BGP] & OSPF [OSPF-BGP] will have their own
   IANA consideration sections.


9. Security Considerations

   This document fully relies on authentication mechanism that an
   implementation of BGP MUST support as specified in [RFC2385]. The
   authentication provided by this mechanism could be done on a per peer
   basis.

   It also relies on security of flooding mechanism being used for
   information distribution.
















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10. Acknowledgments

   I would like to express our thanks to Alvaro Retana, Keyur Patel,
   Barry Friedman & Gargi Nalawade for their valuable comments.


11. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
       Requirement  Levels", RFC 2119, March 1997.

   [RFC2434]  Narten, T., Alvestrand, H., "Guidelines for Writing an
       IANA Considerations Section in RFCs", RFC2434, October 1998.

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
       Signature Option", RFC2385, August 1998.


12. Informative References

   [RFC1771]  Rekhter, Y., and T. Li, "A Border Gateway Protocol 4
       (BGP-4)", RFC 1771, March 1995.

   [IDR-BGP4] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4
       (BGP-4)", Work in Progress (draft-ietf-idr-bgp4-21.txt), April
       2003.

   [RFC1965]  Traina, P., "Autonomous System Confederations for BGP",
       RFC 1965, June 1996.

   [RFC2796]  Bates, T., Chandra, R., and Chen, E., "BGP Route
       Reflection An Alternative to Full Mesh IBGP", RFC 2796, April
       2000.

   [RFC2858]  Bates, T., Rekhter, Y., Chandra, R., Katz, D.,
       "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000

   [IDR-ORF]  Chen, E., Rekhter, Y., "Cooperative Route Filtering
       Capability for BGP-4", draft-ietf-idr-route-filter-08.txt

   [IDR-AS4]  Vohra, Q., Chen, E., "BGP support for four-octet AS number
       space" draft-ietf-idr-as4octets-06.txt, January 2003

   [LINDEM1]  Lindem, A. at all, "Extensions to OSPF for Advertising
       Optional Router Capabilities", draft-lindem-ospf-cap-00.txt, May
       2003

   [ADD-PATH] Walton, D.,at all, "Advertisement of Multiple Paths in



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       BGP" draft-walton-bgp-add-paths-01.txt

   [ISIS-BGP] Raszuk, R., "ISIS Extensions for BGP Peer Discovery" ,
       draft-raszuk-isis-bgp-peer-discovery-00.txt, June 2003 Work in
       progress

   [OSPF-BGP] Raszuk, R., "OSPF Extensions for BGP peer discovery",
       draft-raszuk-ospf-bgp-peer-discovery.txt, Work in Progress


13. Authors' Addresses

      Robert Raszuk
      Cisco Systems, Inc.
      Al. Jerozolimskie 146C
      02-305 Warsaw, Poland
      E-mail: rraszuk@cisco.com


      Pedro Marques
      Juniper Networks, Inc.
      1194 N. Mathilda Ave.
      Sunnyvale, CA 94089
      E-mail: roque@juniper.net


      Chandrashekhar Appanna
      Cisco Systems, Inc
      170 West Tasman Dr
      San Jose, CA 95134
      E-mail: achandra@cisco.com



14. IPR Notices

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   proprietary rights by implementors or users of this specification can



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   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
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