BGP Route Reflection An alternative to full mesh IBGP (RFC1966)
Original Publication Date: 1996-Jun-01
Included in the Prior Art Database: 2019-Feb-12
Internet Society Requests For Comment (RFCs)
T. Bates: AUTHOR [+1]
This document describes the use and design of a method known as "Route Reflection" to alleviate the the need for "full mesh" IBGP. This memo defines an Experimental Protocol for the Internet community.
Network Working Group T. Bates Request for Comments: 1966 cisco Systems Category: Experimental R. Chandra cisco Systems June 1996
BGP Route Reflection An alternative to full mesh IBGP
Status of this Memo
This memo defines an Experimental Protocol for the Internet community. This memo does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
The Border Gateway Protocol  is an inter-autonomous system routing protocol designed for TCP/IP internets. 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. This "full mesh" requirement clearly does not scale when there are a large number of IBGP speakers as is common in many of todays internet networks.
For n BGP speakers within an AS you must maintain n*(n-1)/2 unique IBGP sessions. With finite resources in both bandwidth and router CPU this clearly does not scale.
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". It represents a change in the commonly understood concept of IBGP and the addition of two new
Bates & Chandra Experimental [Page 1]
RFC 1966 BGP Route Reflection June 1996
optional transitive BGP attributes.
2. Design Criteria
Route Reflection was designed to satisfy the following criteria.
Any alternative must be both simple to configure as well as understand.
o Easy Migration
It must be possible to migrate 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 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.
+------ + +-------+ | | IBGP | | | RTR-A |--------| RTR-B | | | | | +-------+ +-------+ \ / IBGP \ ASX / IBGP \ / +-------+ | | | RTR-C | | | +-------+
Figure 1: Full Mesh IBGP
Bates & Chandra...