Paul Jakma wrote:
We already have protocols for this, there is at least one
possibility, IPv6 RAs, so:
- Use IPv6 RAs to advertise both prefixes, with a preferred lifetime
set according to how quickly you want to switch, eg set it equal
to twice the RA interval, or even equal to it.
When the DSL router detects a link has gone down, it simply stops
advertising the relevant prefix.
- We may need to invent protocols to carry valid-source prefix
information across multiple routers in a site. (to update
prefix-advertisement information). I think that's a general IPv6 RA
problem though.
- Other stateful configuration protocols may be used, eg DHCPv6
the server would need to become multi-address aware, an
implementation detail.
Paul,
I had one minor comment on the above.
It might very well be a useful optimization for routers to be able to
express to hosts which prefixes are currently not working for going
outside the site. But I think it would be a mistake to overload the
preferred/deprecated notion for this purpose; if we want to do this we
can just as well add a "temporarily unavailable" bit to the prefix
information options, and that way avoid confusing any hosts that are
not shim6 aware.