A multihomed site is a site that has more than one connection to the
public internet with those connections through either the same or
different ISPs. Sites choose to multihome for several reasons,
especially to improve fault tolerance, perform load balancing, etc.

Multihoming today is done largely by having a site obtain a dedicated
block of address space and then advertising a route for its prefix
through each of its ISP connections. The address block may be from the
so-called provider independent space, or may be a sub-allocation from
one of its ISPs. A site's ISPs in turn advertise the prefix to some or
all of their upstream connections and the route for the prefix may
propagate to all of the routers connected to the default-free zone
(DFZ). As the number of sites multihoming in this manner increase, the
number of routes propagated throughout the DFZ increases and overall
routing stability decreases because of the burden on convergence
time. This WG will seek alternative approaches with better scaling
properties. Specifically, the WG will prefer multihoming solutions
that tend to minimise adverse impacts on the end-to-end routing system
and limit the number of prefixes that need to be advertised in the
Default-Free Zone (DFZ). Just as sites have multiple reasons to choose
multihoming, they may have multiple reasons to want to provide these
benefits more directly to hosts within their sites, for instance,
because some of those hosts may have network stacks capable of
detecting and surviving a provider/prefix change. Phasing in hosts
with
capabilities of multihoming might be part of the Multi6 solution
space.
In the course of this work, the WG may also study the deeper
underlying
questions of identity and location of services, hosts and sites as
they
directly affect multihoming.However, the working group is not
chartered
to make significant changes to the nature of IP addresses or to
inter-domain routing.

This WG will consider the problem of how to multihome sites in
IPv6. The multihoming approaches currently used in IPv4 can of course
be used in IPv6, but IPv6 represents an opportunity for more scalable
approaches. IPv6 differs from IPv4 in ways that may allow for
different approaches to multihoming that are not immediately
applicable to IPv4. For example, IPv6 has larger addresses, hosts
support multiple addresses per interface, and relatively few IPv6
address blocks have been given out (i.e., there are no issues with
legacy allocations as in IPv4). Also, IPv6 deployment is at an early
stage, so modest enhancements to IPv6 could still be proposed.

The WG has already produced a document, RFC 3582, on goals for IPv6
site multihoming architectures. It is recognised that this set of goals
is ambitious and that some goals may conflict with others. The
solution or solutions adopted may only be able to satisfy some of the
goals presented there.

The WG will take on the following tasks:

Produce a document describing how multihoming is done today in IPv4,
including an explanation of both the advantages and limitations of the
approaches.

Produce a document outlining practical questions to be considered
when evaluating proposals meeting the RFC 3582 goals, including
questions concerning upper layer protocols.

Produce a document describing the security threats to be addressed
by multihoming solutions.

Solicit and evaluate specific proposals to multihoming in IPv6
(both existing and new), extract and analyse common architectural
features, and select one or a small number of proposals for further
development. The architectural analysis will include applications
layer
considerations and transport layer considerations, as well as lower
layer issues.

Development of specific solutions will require chartering of work
in the appropriate Area or Areas.