RFC 1092 (rfc1092) - Page 2 of 5
EGP and policy based routing in the new NSFNET backbone
Alternative Format: Original Text Document
RFC 1092 IP EGP and Policy Based Routing February 1989 however, the NSFNET (due to the presence of backdoor routes) does not fit into this model. In the NSFNET the same network may be advertized as reachable by more than one regional network. Besides the fact that the overall NSFNET does not fit into a spanning tree model there are serious concerns with the concept of the "core" (central to the EGP) and its obvious deficiencies. While EGP is going to isolate intra-Regional routing from the intra-NSFNET-Backbone routing, it does not address the issue of false information which may be supplied by regional networks. EGP by itself does not protect a particular network from unwanted and unsolicited representation by some regional network. As an example, if network N1 is reachable through regional network R1 as well as through regional network R2, EGP has no provisions to specify one of these paths as a primary and one as a secondary, since there is not generally accepted interpretation of EGP metrics today. Also, there is nothing in EGP which can prevent one or more regional networks from advertizing other networks (in particular, networks which belong to other regional networks) as reachable with zero distance. This could result in the creation of a "black hole" or at least in suboptimal IP routing. EGP by itself has no provisions to guarantee that routes through the NSFNET Backbone will be preferred over routes through the backdoor routers or vice versa. Policy Based Routing Looking at the problems listed above the appearance of the new factors like autonomy and mutual trust becomes obvious. While trying to achieve the routing functionality required for the new NSFNET backbone we should realize that one of our primary concerns has to be the accommodation of those new factors. This means that some kind of a rudimentary Policy Based Routing method becomes imperative. We would like to emphasize, however, that we are not talking about complete Policy Based Routing, but that we are rather concerned about supporting a minimum subset of a policy functionality to be an initial solution to the above mentioned problems. This requires support and cooperation between the management of each of the networks connected to the NSFNET backbone. We need to support the ability of a particular network N, which belongs to one of the regional networks, to establish a bilateral agreement with one or more regional networks of the type "network N can be reached via one or more regional networks (RN1, RN2, ... RNx)". This allows each network to select one or more representatives at the regional network level. Once this agreement Rekhter
