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BGP Route Reflection - An Alternative to Full Mesh IBGP
RFC 2796

Document type: RFC - Proposed Standard (April 2000; No errata)
Obsoleted by RFC 4456
Updates RFC 1966
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: WG Document
Document shepherd: No shepherd assigned

IESG State: RFC 2796 (Proposed Standard)
Responsible AD: (None)
Send notices to: No addresses provided

Network Working Group                                           T. Bates
Request for Comments: 2796                                 Cisco Systems
Updates: 1966                                                 R. Chandra
Category: Standards Track                                        E. Chen
                                                        Redback Networks
                                                              April 2000

                         BGP Route Reflection -
                    An Alternative to Full Mesh IBGP

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   The Border Gateway Protocol [1] is an inter-autonomous system routing
   protocol designed for TCP/IP internets. Currently in the Internet BGP
   deployments are configured such that that all BGP speakers within a
   single AS must be fully meshed so that any external routing
   information must be re-distributed to all other routers within that
   AS. This represents a serious scaling problem that has been  well
   documented with several alternatives proposed [2,3].

   This document describes the use and design of a method known as
   "Route Reflection" to alleviate the the need for "full mesh" IBGP.

1.  Introduction

   Currently in the Internet, BGP deployments are configured such that
   that all BGP speakers within a single AS must be fully meshed and any
   external routing information must be re-distributed to all other
   routers within that AS.  For n BGP speakers within an AS that
   requires to maintain n*(n-1)/2 unique IBGP sessions.  This "full
   mesh" requirement clearly does not scale when there are a large
   number of IBGP speakers each exchanging a large volume of routing
   information, as is common in many of todays internet networks.

Bates, et al.               Standards Track                     [Page 1]
RFC 2796                  BGP Route Reflection                April 2000

   This scaling problem has been well documented and a number of
   proposals have been made to alleviate this [2,3]. This document
   represents another alternative in alleviating the need for a "full
   mesh" and is known as "Route Reflection". This approach allows a BGP
   speaker (known as "Route Reflector") to advertise IBGP learned routes
   to certain IBGP peers.  It represents a change in the commonly
   understood concept of IBGP, and the addition of two new optional
   transitive BGP attributes to prevent loops in routing updates.

   This document is a revision of RFC1966 [4], and it includes editorial
   changes, clarifications and corrections based on the deployment
   experience with route reflection. These revisions are summarized in
   the Appendix.

2.  Design Criteria

   Route Reflection was designed to satisfy the following criteria.

      o  Simplicity

         Any alternative must be both simple to configure as well as
         understand.

      o  Easy Transition

         It must be possible to transition from a full mesh
         configuration without the need to change either topology or AS.
         This is an unfortunate management overhead of the technique
         proposed in [3].

      o  Compatibility

         It must be possible for non compliant IBGP peers to continue be
         part of the original AS or domain without any loss of BGP
         routing information.

   These criteria were motivated by operational experiences of a very
   large and topology rich network with many external connections.

3.  Route Reflection

   The basic idea of Route Reflection is very simple. Let us consider
   the simple example depicted in Figure 1 below.

Bates, et al.               Standards Track                     [Page 2]
RFC 2796                  BGP Route Reflection                April 2000

                   +-------+        +-------+
                   |       |  IBGP  |       |
                   | RTR-A |--------| RTR-B |
                   |       |        |       |
                   +-------+        +-------+
                         \            /
                     IBGP \   ASX    / IBGP
                           \        /
                            +-------+
                            |       |
                            | RTR-C |
                            |       |

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