RFC 3178 (rfc3178) - Page 2 of 12


IPv6 Multihoming Support at Site Exit Routers



Alternative Format: Original Text Document



RFC 3178     IPv6 Multihoming Support at Site Exit Routers  October 2001


   o  Obtain a portable IPv4 address prefix, and announce it from
      multiple upstream providers.

   o  Obtain a single IPv4 address prefix from ISP A, and announce it
      from multiple upstream providers the site is connected to.

   Since the above two methodologies effectively inject additional
   routes to the worldwide routing table, they have negative impact on
   the worldwide routing table size issue.  They also are not compatible
   with current IPv6 operational practice.

   This document provides a way to configure site exit routers and ISP
   routers, so that the site can achieve better reachability from
   multihomed connectivity, without impacting worldwide routing table
   size issues.  The technique uses multiple distinct IPv6 address
   prefixes, assigned from multiple upstream ISPs.  The technique uses
   an already-defined routing protocol (BGP or RIPng) and tunneling of
   IPv6 packets; therefore, this document introduces no new protocol
   standard (the document describes how to operate the configuration).

   This document is largely based on RFC 2260 [Bates, 1998] by Tony
   Bates.

2.  Goals and non-goals

   The goal of this document is to achieve better packet delivery from a
   site to the outside, or from the outside to the site, even when some
   of the site exit links are down.

   Non goals are:

   o  Choose the "best" exit link as possible.  Note that there can be
      no common definition of the "best" exit link.

   o  Achieve load-balancing between multiple exit links.

   o  Cope with breakage of any of the upstream ISPs.

3.  Basic mechanisms

   We use the technique described in RFC 2260 section 5.2 in our
   configuration.  To summarize, for IPv4-only networks, RFC 2260 says
   that:

   o  We assume that our site is connected to 2 ISPs, ISP-A and ISP-B.






Hagino & Snyder              Informational