Subject: On the use of multiple PA prefixes or a single PI prefix for IPv6 multihoming

From: Cedric de Launois <[email-masked]>
Date: Wed, 22 Sep 2004 15:23:25 +0200

Hi,

There has been discussions recently on the use of multiple
provider-dependent aggregatable (PA) prefixes instead of a single
provider-independent (PI) prefix as the proposed way to multihome in
IPv6.

It is widely known that the use of PA prefixes allows to preserve the
Internet routing tables, thanks to route aggregation.

There exists other advantages as well.

Here is a recent work that aims at evaluating the benefits yielded by
the proposed IPv6 multihoming method over traditional IPv4 multihoming,
in terms of resilience and traffic engineering possibilities. It is
available at :
  http://www.info.ucl.ac.be/people/delaunoi/diversity/index.html

SUMMARY:

This document shows that the use of multiple PA prefixes per sites not
only allows route aggregation but also can be used to reduce end-to-end
delay by leveraging the Internet path diversity.
It is shown that stubs that use multiple PA prefixes can exploit paths
that are otherwise unavailable. Thus, the use of multiple PA prefixes
increases the number of paths available, i.e. the Internet path
diversity. Simulations are used on various topologies to quantify the
path diversity benefits offered by the use of multiple PA prefixes.
The document shows that a dual-homed stub that uses multiple PA prefixes
has already a better Internet path diversity than any multihomed stub
that uses a single provider-independent (PI) prefix, whatever its number
of providers.

Next, it is shown that delays can be improved by leveraging this
Internet path diversity. The use of multiple PA prefixes increases the
number of paths available. Among the new paths, some of them offer
better delays. Simulations show that 60% of the paths can benefit from a
lower delay.

CONCLUSIONS:

These observations show that, from a performance point of view, IPv6
multihomed stubs get benefits from the use of multiple PA prefixes and
should use them instead of a single PI prefix as in IPv4 today.
This study thus strongly encourages the IETF to pursue the development
of IPv6 multihoming solutions relying on the use of multiple PA
prefixes.
The use of such prefixes reduces the size of the BGP routing tables, but
also provides lower delays, more diverse Internet paths, which in turn
yields to better possiblities to balance the traffic load and to support
quality of service.

Cedric