11. Do we expect ISPs to provide reachability for a new and old
prefix concurrently when changing prefixes or do ISPs provide
long-time stable prefixes to IPv6 customers? If "no" on both, then
how do we avoid disconnected sessions on prefix changes?
Personally I like the model of providing reachability for both old
and new during renumbering. But... since an ISP only gets a few
thousand /48 at a time, they may be faced with resource scarcity,
and not have the space (GROAN!!!!).
On the whole, ISPs assign addresses for the period during which you
pay them for a service. I doubt there will be any resource scarcity
leading to revoked assignments while end-sites continue to pay for
service from their ISPs. I don't think an alternative where random /
48s move around between different ASs is a good model to promote.
Well, the scenerio I'm thinking of does not involve a new AS. For
example, if your ISP opens a new site closer to your home, they may
want to route your connectivity into the new site, which could very
well involve renumbering.
So, Ilijtsch's question is important.
I am told that today the best way to do such a migration in IPv4 is
for ISPs to pick a time to move customers to the new numbers, and use
ever-decreasing DHCP lease times to insure that users renumber as
close to that time as possible - but not to overlap the address spaces
for any time.