RFC 2260 (rfc2260) - Page 2 of 12

Scalable Support for Multi-homed Multi-provider Connectivity

RFC 2260                      Multihoming                   January 1998


   to maintain a route for every multi-homed enterprise that is
   connected to multiple ISPs does not provide an adequate scaling.
   Moreover, given the nature of the Internet, this document assumes
   that any approach to handle routing for such enterprises should
   minimize the amount of coordination among ISPs, and especially the
   ISPs that are not directly connected to these enterprises.

   There is a difference of opinions on whether the driving factors
   behind multi-homing to multiple ISPs could be adequately addressed by
   multi-homing just to a single ISP, which would in turn eliminate the
   negative impact of multi-homing on the Internet routing system.
   Discussion of this topic is beyond the scope of this document.

   The focus of this document is on the routing and addressing
   strategies that could reduce the routing overhead due to multi-homed
   enterprises connected to multiple ISPs in the Internet routing
   system.

   The strategies described in this document are equally applicable to
   both IPv4 and IPv6.

4. Address allocation and assignment

   A multi-homed enterprise connected to a set of ISPs would be
   allocated a block of addresses (address prefix) by each of these ISPs
   (an enterprise connected to N ISPs would get N different blocks).
   The address allocation from the ISPs to the enterprise would be based
   on the "address-lending" policy [RFC 2008]. The allocated addresses
   then would be used for address assignment within the enterprise.

   One possible address assignment plan that the enterprise could employ
   is to use the topological proximity of a node (host) to a particular
   ISP (to the interconnect between the enterprise and the ISP) as a
   criteria for selecting which of the address prefixes to use for
   address assignment to the node. A particular node (host) may be
   assigned address(es) out of a single prefix, or may have addresses
   from different prefixes.

5. Routing information exchange

   The issue of routing information exchange between an enterprise and
   its ISPs is decomposed into the following components:

      a) reachability information that an enterprise border router
      advertises to a border router within an ISP

      b) reachability information that a border router within an ISP
      advertises to an enterprise border router



Bates & Rekhter              Informational