Re: slaac-renum: Valid Lifetimes

[Philip Homburg <[e-mail]>]

>However, after discussing this with a number of developers from 
>different OSes there seems to be agreement that this value Valid 
>Lifetime is still to large, and that it would be more sensible to use 
>something like: 2 * Router Lifetime  (which is still very conservative).

I think we should be extremely creaful with this. This a a host overriding
parameters provided by the network. So we effectively limit how people
can run their networks.

In particular, I can imagine that some people may want long lifetimes to
make sure that if a router dies, local communication remains possible.

So I think limiting the preferred lifetime is relatively safe. Maybe the
valid lifetime can be reduced to one day, but shorter is probably a bad idea.

That said, if we make valid lifetime a small multiple of router lifetime,
then people who want a long valid lifetime can increase router lifetime.
However, a long router lifetime may come back to bite us at other points.

So I would go for something like:
the limit on valid lifetime = max(1 day, 2 * router lifetime).

I assume that in most cases, the algorithm ill agressively limit the valid
lifetime of prefixes that are no longer announced. I.e., this blanked cap
is only for the cases where the algorithm fails.