RFC 1403 (rfc1403) - Page 2 of 17

BGP OSPF Interaction

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RFC 1403                  BGP OSPF Interaction              January 1993


1.  Introduction

   This document defines the various criteria to be used when designing
   an Autonomous System Border Routers (ASBR) that will run BGP
   [RFC 1267] with other ASBRs external to the AS, and OSPF [RFC 1247] as
   its IGP.

   This document defines how the following fields in OSPF and attributes
   in BGP are to be set when interfacing between BGP and OSPF at an
   ASBR:

           OSPF cost and type      vs. BGP INTER-AS METRIC
           OSPF tag                vs. BGP ORIGIN and AS_PATH
           OSPF Forwarding Address vs. BGP NEXT_HOP

   For a more general treatise on routing and route exchange problems,
   please refer to [ROUTE-LEAKING] and [NEXT-HOP] by Philip Almquist.

   This document uses the two terms "Autonomous System" and "Routing
   Domain".  The definitions for the two are below:

   The term Autonomous System is the same as is used in the BGP-3 RFC
   [RFC 1267], given below:

        "The use of the term Autonomous System here stresses the fact
        that, even when multiple IGPs and metrics are used, the
        administration of an AS appears to other ASs to have a single
        coherent interior routing plan and presents a consistent picture
        of what networks are reachable through it.  From the standpoint
        of exterior routing, an AS can be viewed as monolithic:
        reachability to networks directly connected to the AS must be
        equivalent from all border gateways of the AS."

   The term Routing Domain was first used in [ROUTE-LEAKING] and is
   given below:

          "A Routing Domain is a collection of routers which coordinate
          their routing knowledge using a single (instance of) a routing
          protocol."

     This document follows the conventions embodied in the Host
     Requirements RFCs [RFC 1122, RFC 1123], when using the terms "MUST",
     "SHOULD", and "MAY" for the various requirements.








Varadhan
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