On Oct 26, 2009, Andrew G. Malis wrote:
Note that IPv6 NAT makes multihoming to different ISPs much easier as
well.
One thing that IPv6 NAT has in advantage to IPv4 NAT is that it can be
stateless, isomorphic, and port transparent [...]
Right. There is one limitation, though: With stateless NAT'ing alone,
failover of active communication sessions between providers is not
possible. This is because statelessness requires one-to-one address
mappings, hence a separate internal prefix for every provider-assigned
external prefix. Many-to-one address mapping, such as by mapping a
single internal prefix onto multiple external prefixes, would require
stateful demultiplexing.
You can avoid above limitation with some support in the routing system.
[1] describes this. It comes at a cost, however: It requires selective
route announcements internally in lieu of a default route, as well as
redirects of incoming communication sessions.
- Christian
[1] http://christianvogt.mailup.net/pub/2008/vogt-2008-six-one-router-design.pdf
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