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+Network Working Group                                          D. Haskin
+Request for Comments: 1397                 Bolt Beranek and Newman, Inc.
+                                                            January 1993
+
+
+                     Default Route Advertisement In
+         BGP2 And BGP3 Versions Of The Border Gateway Protocol
+
+Status of this Memo
+
+   This RFC specifies an IAB standards track protocol for the Internet
+   community, and requests discussion and suggestions for improvements.
+   Please refer to the current edition of the "IAB Official Protocol
+   Standards" for the standardization state and status of this protocol.
+   Distribution of this memo is unlimited.
+
+Abstract
+
+   This document specifies the recommendation of the BGP Working Group
+   on default route advertisement support in BGP2 [1] and BGP3 [2]
+   versions of the Border Gateway Protocol.
+
+   This recommendation only applies to BGP2 and BGP3 versions of the
+   Border Gateway Protocol since starting with the BGP4 [3] version a
+   default route advertisement capability is built in the protocol.
+
+1. Overview
+
+   The purpose of the default route advertisement capability is to
+   advertise the IP address of a border gateway which can be used as the
+   default next hop to destinations that are not listed explicitly in
+   the BGP peer's routing table.
+
+   This capability will allow routers, that are unable to maintain a
+   complete routing table (e.g., due to its size) to learn a border
+   gateway that is ready to handle the default traffic.  Also, in
+   contrast to static defaults, if there is more than one default
+   gateway, this would make it possible for a BGP speaker to express a
+   preference for one over the other.  It also reduces the need to
+   configure default routes in routers.
+
+2. Default Route Advertisement
+
+   A default route is advertised in an UPDATE message that carries
+   reachability information for network 0.0.0.0.  A Network field of
+   such an UPDATE message must contain the IP address 0.0.0.0 as the
+   indication that it carries a default route.  The NEXT_HOP path
+   attribute of such a message provides the IP address of a border
+
+
+
+Haskin                                                          [Page 1]
+
+RFC 1397               Default Routes in Old BGPs           January 1993
+
+
+   gateway that can be used as a default next hop to destinations that
+   are not listed in the BGP peer's routing table.  The value of the
+   ORIGIN attribute should be 2 (INCOMPLETE).  The AS_PATH attribute
+   should be constructed according to the same rules that apply to a
+   conventional network advertisement.
+
+   If multiple default routes are advertised by a BGP speaker,  the
+   INTER-AS-METRIC path attribute can be included in the corresponding
+   UPDATE messages to express  preference levels for entry points to the
+   same AS.
+
+   The UNREACHABLE path attribute is used to indicate that a previously
+   advertised default route has become unreachable.
+
+   UPDATE messages containing the default route advertisements should be
+   handled according to the rules that apply to all other UPDATE
+   messages.  If multiple default route are acquired by a BGP speaker, a
+   route is selected according to the local policies adopted by this BGP
+   speaker.
+
+References
+
+   [1] Lougheed, K., and Y. Rekhter, "A Border Gateway Protocol (BGP)",
+       RFC 1163, cisco Systems, T.J. Watson Research Center, IBM Corp.,
+       June 1990.
+
+   [2] Lougheed, K., and Y. Rekhter, "A Border Gateway Protocol 3 (BGP-
+       3)", RFC 1267, cisco Systems, T.J. Watson Research Center, IBM
+       Corp., October 1991.
+
+   [3] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
+       Work in Progress, T.J. Watson Research Center, IBM Corp., cisco
+       Systems, December 1992.
+
+Security Considerations
+
+   Security issues are not discussed in this memo.
+
+Author's Address
+
+   Dimitry Haskin
+   Bolt, Beranek & Newman
+   150 Cambridge Park Drive
+   Cambridge, MA 02140
+
+   Phone: 617-873-8609
+   Email: dhaskin@bbn.com
+
+
+
+
+Haskin                                                          [Page 2]
+
+\ No newline at end of file