--- 1/draft-ietf-idr-route-reflect-v2-01.txt 2006-02-04 23:31:51.000000000 +0100 +++ 2/draft-ietf-idr-route-reflect-v2-02.txt 2006-02-04 23:31:51.000000000 +0100 @@ -1,37 +1,38 @@ - INTERNET-DRAFT Tony Bates - Ravi Chandra + Ravi Chandra Enke Chen Cisco Systems - April 1999 + September 1999 - BGP Route Reflection - An alternative to full mesh IBGP - + BGP Route Reflection - + An Alternative to Full Mesh IBGP + Status of this Memo - This document is an Internet Draft. 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. + 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 obsoleted by - other documents at any time. It is not appropriate to use Internet - Drafts as reference material or to cite them other than as a "working - draft" or "work in progress". + Internet-Drafts are draft documents valid for a maximum of six months + and may be updated, replaced, or obsoleted by other documents at any + time. It is inappropriate to use Internet-Drafts as reference + material or to cite them other than as "work in progress." - Please check the I-D abstract listing contained in each Internet - Draft directory to learn the current status of this or any other - Internet Draft. + 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 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]. @@ -52,20 +53,24 @@ 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. + 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 @@ -78,24 +83,25 @@ 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 | @@ -110,21 +116,21 @@ 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 advertise IBGP learned routes to IBGP peers, 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. - +------ + +-------+ + +-------+ +-------+ | | | | | RTR-A | | RTR-B | | | | | +-------+ +-------+ \ / IBGP \ ASX / IBGP \ / +-------+ | | | RTR-C | @@ -234,42 +241,42 @@ defines the following attributes to detect and avoid routing information loops: ORIGINATOR_ID ORIGINATOR_ID is a new optional, non-transitive BGP attribute of Type code 9. This attribute is 4 bytes long and it will be created by a RR in reflecting a route. This attribute will carry the ROUTER_ID of the originator of the route in the local AS. A BGP speaker should not create an ORIGINATOR_ID attribute if one already exists. A router - should ignore a route received with its ROUTER_ID as the - ORIGINATOR_ID. + which recognizes the ORIGINATOR_ID attribute should ignore a route + received with its ROUTER_ID as the ORIGINATOR_ID. CLUSTER_LIST Cluster-list is a new optional, non-transitive BGP attribute of Type code 10. It is a sequence of CLUSTER_ID values representing the reflection path that the route has passed. It is encoded as follows: 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Attr. Flags |Attr. Type Code| Length | value ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where Length is the number of octets. When a RR reflects a route, it must prepend the local CLUSTER_ID to the CLUSTER_LIST. If the CLUSTER_LIST is empty, it must create a new one. Using this attribute an RR can identify if the routing information is looped back to the same cluster due to mis- configuration. If the local CLUSTER_ID is found in the cluster-list, - the advertisement received will be ignored. + the advertisement received should be ignored. 8. Implementation Considerations Care should be taken to make sure that none of the BGP path attributes defined above can be modified through configuration when exchanging internal routing information between RRs and Clients and Non-Clients. Their modification could potential result in routing loops. In addition, when a RR reflects a route, it should not modify the @@ -323,44 +330,50 @@ is the POP-based reflection, in which each POP maintains its own route reflectors serving clients in the POP, and all route reflectors are fully meshed. In addition, clients of the reflectors in each POP are often fully meshed for the purpose of optimal intra-POP routing, and the intra-POP IGP metrics are configured to be better than the inter-POP IGP metrics. 10. Security This extension to BGP does not change the underlying security issues - inherent in the existing IBGP. + inherent in the existing IBGP [5]. 11. Acknowledgments - The authors would like to thank Dennis Ferguson, John Scudder, Paul Traina and Tony Li for the many discussions resulting in this work. This idea was developed from an earlier discussion between Tony Li and Dimitri Haskin. In addition, the authors would like to acknowledge valuable review and suggestions from Yakov Rekhter on this document, and helpful - comments from Tony Li, Rohit Dube, and John Scudder on Section 9. + comments from Tony Li, Rohit Dube, and John Scudder on Section 9, and + from Bruce Cole. 12. References [1] Rekhter, Y., and Li, T., "A Border Gateway Protocol 4 (BGP-4)", RFC1771, March 1995. [2] Haskin, D., "A BGP/IDRP Route Server alternative to a full mesh routing", RFC1863, October 1995. [3] Traina, P. "Limited Autonomous System Confederations for BGP", RFC1965, June 1996. + [4] Bates, T., and Chandra, R., "BGP Route Reflection An alternative + to full mesh IBGP", RFC1966, June 1996. + + [5] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 Sig- + nature Option", RFC2385, August 1998. + 13. Author's Addresses Tony Bates Cisco Systems 170 West Tasman Drive email: tbates@cisco.com Ravishanker Chandrasekeran (Ravi Chandra)