Network Working Group T. Bates
Request for Comments: 2796 Cisco Systems
Updates: 1966 R. Chandra
Category: Standards Track E. Chen
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 (C) The Internet Society (2000). All Rights Reserved.
The Border Gateway Protocol  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.
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 , and it includes editorial
changes, clarifications and corrections based on the deployment
experience with route reflection. These revisions are summarized in
2. Design Criteria
Route Reflection was designed to satisfy the following criteria.
Any alternative must be both simple to configure as well as
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 .
It must be possible for non compliant IBGP peers to continue be
part of the original AS or domain without any loss of BGP
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 |