BGP4/IDRP for IP---OSPF Interaction
RFC 1745

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Network Working Group                                       K.  Varadhan
Request for Comments: 1745                                  OARnet & ISI
Category: Standards Track                                       S. Hares
                                                            NSFnet/Merit
                                                              Y. Rekhter
                                  T.J. Watson Research Center, IBM Corp.
                                                           December 1994

                  BGP4/IDRP for IP---OSPF Interaction

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This memo defines the various criteria to be used when designing an
   Autonomous System Border Router (ASBR) that will run either BGP4 or
   IDRP for IP with other ASBRs external to the AS and OSPF as its IGP.

Table of Contents

   1.  Introduction .................................................  2
   2.  Reachability Information Exchange ............................  4
   2.1.  Exporting OSPF information into BGP/IDRP  ..................  4
   2.2.  Importing BGP/IDRP information into OSPF ...................  6
   3.  BGP/IDRP Identifier and OSPF router ID .......................  7
   4.  Setting OSPF tags, ORIGIN and PATH attributes ................  8
   4.1.  Configuration parameters for setting the OSPF tag .......... 10
   4.2.  Manually configured tags ................................... 10
   4.3.  Automatically generated tags ............................... 11
   4.3.1. Tag = <Automatic = 1, Complete = 0, PathLength = 00> ...... 11
   4.3.2. Tag = <Automatic = 1, Complete = 0, PathLength = 01> ...... 11
   4.3.3. Tag = <Automatic = 1, Complete = 0, PathLength = 10> ...... 12
   4.3.4. Tag = <Automatic = 1, Complete = 1, PathLength = 00> ...... 12
   4.3.5. Tag = <Automatic = 1, Complete = 1, PathLength = 01> ...... 12
   4.3.6. Tag = <Automatic = 1, Complete = 1, PathLength = 10> ...... 13
   4.4.  Miscellaneous tag settings ................................. 14
   5.  Setting OSPF Forwarding Address and BGP NEXT_HOP attribute ... 14
   6.  Changes from the BGP 3 - OSPF interactions document .......... 15
   7.  Security Considerations ...................................... 16
   8.  Acknowledgements ............................................. 16
   9.  Bibliography ................................................. 16

Varadhan, Hares & Rekhter                                       [Page 1]
RFC 1745          BGP4/IDRP for IP - OSPF Interaction      December 1994

   10.  Appendix .................................................... 18
   11.  Authors' Present Addresses .................................. 19

1.  Introduction

   This document defines the various criteria to be used when designing
   an Autonomous System Border Router (ASBR) that will run BGP4
   [RFC1654] or IDRP for IP [IDRP] with other ASBRs external to the AS,
   and OSPF [RFC1583] as its IGP.

   All future references of BGP in this document will refer to BGP
   version 4, as defined in [RFC1654].  All reference to IDRP are
   references to the Inter-Domain Routing Protocol (ISO 10747) which has
   been defined by the IDRP for IP document [IDRP] for use in Autonomous
   Systems.

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

   IDRP came out of the same work as BGP, and may be consider a follow
   on to BGP-3 and BGP-4.  Most fields defined in the interaction
   between BGP and IDRP are named the same.  Where different, the IDRP
   fields are shown separately.

           BGP/IDRP MULTI_EXIT_DISC

           BGP ORIGIN and AS_PATH/AS_SET     vs. OSPF tag
           IDRP EXT_INFO and RD_PATH/RD_SET

           BGP/IDRP NEXT_HOP                 vs. OSPF Forwarding Address

           BGP/IDRP LOCAL_PREF               vs. OSPF cost and type

   IDRP contains RD_PATH and RD_SET fields which serves the same purpose
   as AS_PATH and AS_SET fields for IDRP for IP.  In this document, we
   will use the terms PATH and SET to refer to the BGP AS_PATH and
   AS_SET, or the IDRP RD_PATH and RD_SET fields respectively, depending
   on the context of the protocol being used.

   Both IDRP and BGP provide a mechanism to indicate whether the routing
   information was originated via an IGP, or some other means.  In IDRP,
   if route information is originated by means other than an IGP, then
   the EXT_INFO attribute is present.  Likewise, in BGP, if a route
   information is originated by means other than an IGP, then the ORIGIN
   attribute is set to <EGP> or <INCOMPLETE>.  For the purpose of this