Re: [v6ops] A common problem with SLAAC in "renumbering" scenarios

[Philip Homburg <[e-mail]>]

>So while I am generally sympathetic to this draft and what it tries to 
>achieve (especially the part where it ties the router announcing something 
>to what it's later announcing, and lack of something means it's implicitly 
>zero preferred time for that), we need to figure out a few more things 
>first. RFC7084 was informational which made it fairly easy to get through, 
>now you're proposing a standards track document so we need to make sure 
>everything works. Changing all hosts is a big thing.

I think changing host behavior is good in this case if we can make hosts more
robust. I prefer the network to do the right thing, but reality is that that
will not always happen, so it is good to have robust hosts.

That said, I don't like playing games with the valid lifetime. Changes to 
preferred lifetime are relatively benign, setting the valid lifetime of a
prefix to zero may have more serious consequences.

I think the algorithm can be simplified to:
- When a RA is received that contains a PIO with the A bit set, then set the
  preferred lifetime to zero for all addresses derived from prefixes that were
  announced by the same router and that are not covered by the current RA.

In extreme cases this may cause the preferred lifetime to ping-pong. But that
just causes source address selection to become more random, which should be
fine.