RFC 1102 (rfc1102) - Page 2 of 22
Policy routing in Internet protocols
Alternative Format: Original Text Document
RFC 1102 Policy Routing in Internet Protocols May 1989 to reduce the amount of global information. The problem of adding structure to the space of ARs is an exercise for later study.) Before a PR can be used, however, it must be reduced to more concrete terms; a series of gateways which connect the sequence of ARs. These gateways will be called Policy Gateways. Presently, the closest mechanism to policy routing in the Internet is EGP, the Exterior Gateway Protocol. EGP was constructed to permit regions of the Internet to communicate reachability information, even though they did not totally share trust. In this respect, the regions hooked together by EGP could each be viewed as Administrative Regions. However, the mechanisms of EGP imposed a topological restriction on the interconnection of the Administration Regions. In practice, this has proved unsatisfactory. Policy matters are driven by human concerns, and these have not turned out to be amenable to topological constraints, or indeed to constraints of almost any sort. The proposals in this memo are designed to permit as wide a latitude as possible in the construction and enforcement of policies. In particular, no topological restrictions are assumed. In general, the approach taken in this memo is driven by the belief that since policies reflect human concerns, the system should primarily be concerned with enforcement of policy, rather than synthesis of policy. The proposal permits both end points and transit services to express and enforce local policy concerns. 3. Policy Routes Almost all approaches to policy control share, to some degree, the idea of a Policy Route. The distinguishing component of a policy approach is the procedure by which the Policy Route is synthesized. One approach to synthesizing routes is to associate with each distinct policy a subset of all the gateways in the system, and then run a routing algorithm across the subset of the gateways. This approach has several drawbacks. It requires a distinct routing computation for every policy, which may be prohibitively expensive. It requires the global agreement on the nature and scope of each policy, which is at odds with the desire of Administrative Regions to establish their own independent policy assertions. Finally, it almost inevitably implies a topological restriction on the interconnection of regions. Another synthesis approach is to have each Policy Gateway examine incoming packets and determine, based on local policy constraints, the most appropriate next AR. This approach might possibly work, but again has several drawbacks. First, it implies a substantial amount of computation at each Policy Gateway. More importantly, it removes the route selection from the location where it would most naturally Clark
