BGP Route Reflection An alternative to full mesh IBGP
RFC 1966
Document | Type |
RFC - Experimental
(June 1996; No errata)
Obsoleted by RFC 4456
Updated by RFC 2796
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Authors | Ravi Chandra , Tony Bates | ||
Last updated | 2013-03-02 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | WG state | WG Document | |
Document shepherd | No shepherd assigned | ||
IESG | IESG state | RFC 1966 (Experimental) | |
Consensus Boilerplate | Unknown | ||
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
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. Abstract The Border Gateway Protocol [1] 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. 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. 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. o Simplicity 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 [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. +------ + +-------+ | | IBGP | | | RTR-A |--------| RTR-B | | | | | +-------+ +-------+ \ / IBGP \ ASX / IBGP \ / +-------+ | | | RTR-C | | | +-------+ Figure 1: Full Mesh IBGP Bates & Chandra Experimental [Page 2] RFC 1966 BGP Route Reflection June 1996 In ASX there are three IBGP speakers (routers RTR-A, RTR-B and RTR- C). With the existing BGP model, if RTR-A receives an external route and it is selected as the best path it must advertise the external route to both RTR-B and RTR-C. RTR-B and RTR-C (as IBGP speakers) will not re-advertise these IBGP learned routes to other IBGP speakers. If this rule is relaxed and RTR-C is allowed to reflect IBGP learned routes, then it could re-advertise (or reflect) the IBGP routes learned from RTR-A to RTR-B and vice versa. This would eliminate the need for the IBGP session between RTR-A and RTR-B as shown in Figure 2 below. +------ + +-------+ | | | |Show full document text