Policy routing in Internet protocols
RFC 1102

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Network Working Group                                           D. Clark
Request for Comments: 1102        M.I.T. Laboratory for Computer Science
                                                                May 1989

                  Policy Routing in Internet Protocols

1. Status of this Memo

   The purpose of this RFC is to focus discussion on particular problems
   in the Internet and possible methods of solution.  No proposed
   solutions in this document are intended as standards for the
   Internet.  Distribution of this memo is unlimited.

2. Introduction

   An integral component of the Internet protocols is the routing
   function, which determines the series of networks and gateways a
   packet will traverse in passing from the source to the destination.
   Although there have been a number of routing protocols used in the
   Internet, they share the idea that one route should be selected out
   of all available routes based on minimizing some measure of the
   route, such as delay.  Recently, it has become important to select
   routes in order to restrict the use of network resources to certain
   classes of customers.  These considerations, which are usually
   described as resource policies, are poorly enforced by the existing
   technology in the Internet.  This document proposes an approach to
   integrating policy controls into the Internet.

   I assume that the resources of the Internet: networks, links, and
   gateways, are partitioned into Administrative Regions or ARs.  Each
   AR is governed by a somewhat autonomous administration, with distinct
   goals as to the class of customers it intends to serve, the qualities
   of service it intends to deliver, and the means for recovering its
   cost.  To construct a route across the Internet, a sequence of ARs
   must be selected that collectively supply a path from the source to
   the destination.  This sequence of ARs will be called a Policy Route,
   or PR.  Each AR through which a Policy Route passes will be concerned
   that the PR has been properly constructed.  To this end, each AR may
   wish to insure that the user of the PR is authorized, the requested
   quality of service is supported, and that the cost of the service can
   be recovered.

   In the abstract, a Policy Route is a series of ARs, which are assumed
   to be named with globally distinct identifiers.  (The requirement for
   global names for ARs suggests that the name space of ARs is flat.
   That simplifying assumption is made in this RFC, but it should be
   possible to extend the scheme described here to permit nesting of ARs

Clark                                                           [Page 1]
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