EGP and policy based routing in the new NSFNET backbone (RFC1092)
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2019-Feb-15
Internet Society Requests For Comment (RFCs)
This memo discusses implementation decisions for routing issues in the NSFNET, especially in the NSFNET Backbone. Of special concern is the restriction of routing information to advertize the best route as established by a policy decision.
Network Working Group J. Rekhter Request for Comments: 1092 T. J. Watson Research Center February 1989
EGP and Policy Based Routing in the New NSFNET Backbone
Status of this Memo
This memo discusses implementation decisions for routing issues in the NSFNET, especially in the NSFNET Backbone. Of special concern is the restriction of routing information to advertize the best route as established by a policy decision. Distribution of this memo is unlimited.
The NSFNET backbone routes packets between the Regionals Networks to which it is connected, (i.e., the packets arriving at a backbone entry node are routed to an exit node). How they travel through the network is determined by two components:
the NSFNET backbone routing protocol/algorithm, and
additional information about the externally connected networks.
This paper is concerned with how reachability information between the external networks and the NSFNET backbone is exchanged so that packets can be routed to the correct destination by using a reasonable path.
EGP as reachability protocol
The EGP (Exterior Gateway Protocol) routing method will be used to exchange reachability information between the NSFNET backbone and the regional networks.
There are several problems with using EGP as a reachability protocol for routing in a meshed environment. Some EGP components require further definitions for the NSFNET backbone - regional network interactions. It should be noted that the use of EGP is only viewed as an interim measure until better inter autonomous system protocols are defined and widely deployed for gateways used by regional networks.
The following is a list of some EGP problems and issues:
The EGP model assumes an engineered spanning tree topology,
Rekhter [Page 1]
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. Thi...