RFC 1364 (rfc1364) - Page 2 of 14
BGP OSPF Interaction
Alternative Format: Original Text Document
RFC 1364 BGP OSPF Interaction September 1992
1. Introduction
This document defines the various criteria to be used when designing
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."
2. Route Exchange
This section discusses the constraints that must be met to exchange
routes between an external BGP session with a peer from another AS
and internal OSPF routes.
BGP does not carry subnet information in routing updates. Therefore,
when referring to a subnetted network in the OSPF routing domain, we
consider the equivalent network route in the context of BGP.
Varadhan