Network Working Group D. Haskin
Request For Comments: 1863 Bay Networks, Inc.
Category: Experimental October 1995
A BGP/IDRP Route Server alternative to a full mesh routing
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.
This document describes the use and detailed design of Route Servers
for dissemination of routing information among BGP/IDRP speaking
The intention of the proposed technique is to reduce overhead and
management complexity of maintaining numerous direct BGP/IDRP
sessions which otherwise might be required or desired among routers
within a single routing domain as well as among routers in different
domains that are connected to a common switched fabric (e.g. an ATM
Current deployments of Exterior Routing protocols, such as the Border
Gateway Protocol [BGP4] and the adaptation of the ISO Inter-Domain
Routing Protocol [IDRP], require that all BGP/IDRP routers, which
participate in inter-domain routing (border routers) and belong to
the same routing domain, establish a full mesh connectivity with each
other for purpose of exchanging routing information acquired from
other routing domains. In large routing domains the number of intra-
domain connections that needs to be maintained by each border route
can be significant.
In addition, it may be desired for a border router to establish
routing sessions with all border routers in other domains which are
reachable via a shared communication media. We refer to routers that
are directly reachable via a shared media as adjacent routers. Such
direct peering allows a router to acquire "first hand" information
about destinations which are directly reachable through adjacent
routers and select the optimum direct paths to these destinations.
Establishment of BGP/IDRP sessions among all adjacent border routers
would result in a full mesh routing connectivity. Unfortunately for
Haskin Experimental [Page 1]RFC 1863 A BGP/IDRP Route Server October 1995
a switched media as ATM, SMDS or Frame Relay network which may
inter-connect a large number of routers, due to the number of
connections that would be needed to maintain a full mesh direct
peering between the routers, makes this approach impractical.
In order to alleviate the "full mesh" problem, this paper proposes to
use IDRP/BGP Route Servers which would relay external routes with all
of their attributes between client routers. The clients would
maintain IDRP/BGP sessions only with the assigned route servers
(sessions with more than one server would be needed if redundancy is
desired). All routes that are received from a client router would be
propagated to other clients by the Route Server. Since all external
routes and their attributes are relayed unmodified between the client
routers, the client routers would acquire the same routing
information as they would via direct peering. We refer to such
arrangement as virtual peering. Virtual peering allows client
routers independently apply selection criteria to the acquired
external routes according to their local policies as they would if a
direct peering were established.
The routing approach described in this paper assumes that border
routers possess a mechanism to resolve the media access address of
the next hop router for any route acquired from a virtual peer.
It is fair to note that the approach presented in this paper only
reduces the number of routing connection each border router needs to
maintain. It does not reduce the volume of routing information that
needs to maintained at each border router.
Besides addressing the "full mesh" problems, the proposal attempts
to achieve the following goals:
- to minimize BGP/IDRP changes that need to be implemented in client
routers in order to inter-operate with route servers;
- to provide for redundancy of distribution of routing information to
route server clients;
- to minimize the amount of routing updates that have to be sent to
route server clients;
- to provide load distribution between route servers;
- to avoid an excessive complexity of the interactions between Route
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