--- 1/draft-ietf-idr-route-reflect-01.txt 2006-02-04 23:31:50.000000000 +0100 +++ 2/draft-ietf-idr-route-reflect-02.txt 2006-02-04 23:31:50.000000000 +0100 @@ -1,20 +1,20 @@ INTERNET-DRAFT Tony Bates - MCI + MCI Ravi Chandra cisco Systems - March 1996 + April 1996 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. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by @@ -34,26 +34,26 @@ 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 today, 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. + 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 @@ -108,21 +108,21 @@ 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-C as shown in Figure + need for the IBGP session between RTR-A and RTR-B as shown in Figure 2 below. +------ + +-------+ | | | | | RTR-A | | RTR-B | | | | | +-------+ +-------+ \ / IBGP \ ASX / IBGP \ / @@ -185,43 +185,43 @@ the following depending on the type of the peer it is receiving the best path from: 1) A Route from a Non-Client peer Reflect to all other Clients. 2) A Route from a Client peer Reflect to all the Non-Client peers and also to the - Client peers (Hence the Client peers are not required - to be fully meshed). + Client peers other than the originator. (Hence the + Client peers are not required to be fully meshed). 3) Route from an EBGP peer Send to all the Client and Non-Client Peers. An Autonomous System could have many RRs. A RR treats other RRs just like any other internal BGP speakers. A RR could be configured to have other RRs in a Client group or Non-client group. In a simple configuration the backbone could be divided into many clusters. Each RR would be configured with other RRs as Non-Client peers (thus all the RRs will be fully meshed.). The Clients will be configured to maintain IBGP session only with the RR in their cluster. Due to route reflection, all the IBGP speakers will receive reflected routing information. It is normal in a Autonomous System to have BGP speakers that do not - understand the concept of Route-Reflectors (let us call them as + understand the concept of Route-Reflectors (let us call them conventional BGP speakers). The Route-Reflector Scheme allows such conventional BGP speakers to co-exist. Conventional BGP speakers - could be either members of Non-Client group or Client group. This + could be either members of a Non-Client group or a Client group. This allows for an easy and gradual migration from the current IBGP model to the Route Reflection model. One could start creating clusters by configuring a single router as the designated RR and configuring other RRs and their clients as normal IBGP peers. Additional clusters can be created gradually. 6. Redundant RRs Usually a cluster of clients will have a single RR. In that case, the cluster will be identified by the ROUTER_ID of the RR. However, this @@ -236,22 +236,23 @@ configuration to form route re-distribution loops. The Route Reflection method 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. 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 If routing information - comes back to the originator, it must be ignored. + ORIGINATOR_ID attribute if one already exists. A route reflector + must never send routing information back to the router specified in + 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 ... @@ -269,27 +270,27 @@ 8. Implementation and Configuration 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. This could result is looping of routes. In some implementations, modification of the BGP path attribute, NEXT_HOP is possible. For example, there could be a need for a RR to modify NEXT_HOP for EBGP learned routes sent to its internal peers. - However, this must not be possible for an RR to set on reflected IBGP + However, it must not be possible for an RR to set on reflected IBGP routes as this breaks the basic principle of Route Reflection and - will result in potential black holes. + will result in potential black holeing of traffic. An RR should not modify any AS-PATH attributes (i.e. LOCAL_PREF, MED, - DPA)that could change consistent route selection. This could - resulting in potential loops. + DPA)that could change consistent route selection. This could result + in potential loops. The BGP protocol provides no way for a Client to identify itself dynamically as a Client to an RR configured BGP speaker and the simplest way to achieve this is by manual configuration. 9. Security Security considerations are not discussed in this memo. 10. Acknowledgments