Re: draft-shirasaki-dualstack-service-02.txt CPE assigned Host Address Lifetime issue

[SHIRASAKI Yasuhiro <yasuhiro@nttv6.jp>]

On Mon, 16 Feb 2004 11:37:51 +0900,
JINMEI Tatuya / 神明達哉 <jinmei@isl.rdc.toshiba.co.jp> wrote:
> >> So now the hosts (PCs) will have an old  non-link-local IPv6 address, with
> >> its lifetime still valid for the next week or month, and receives a new
> >> non-link-local IPv6 address. When sending out packets, it will have to make
> >> a default address selection based on the two source addresses. It will have
> >> good chance of selecting the old address, which the BRAS doesn't have a clue
> >> when forwarding packet back to this (destination) address.
> 
> > I've just checked two implementations and noticed a different behavior
> > against prefix changes. When the CPE changed advertising prefixes
> > in a flash, one implementation did the things as you mentioned,
> > but the another one has revoked an old prefix immidiately and started
> > communications with a new prefix only. If all hosts behave as
> > the latter implementation, we don't need any special treatment
> > with prefix changes...
> 
> Please let me check, are you talking about a host that behaves like
> this?
> 
> - the host receives a prefix P via RA from a router, and configures an
>   address P:A.
> - then the router stops advertising the prefix P, and starts
>   advertising another prefix Q.
> - the host receives the new RAs with prefix Q, and configures a new
>   address Q:A.  At this stage, the preferred and valid lifetimes of
>   the old address does not expire.  However, the host never uses the
>   old address as the source address even if RFC3484 suggests the
>   old address be preferred.
> 
> If so, I'd say the host is not fully compliant (at least not compliant
> to RFC3484), and network operators should not assume such a behavior.

Exactly.

I got your point, but if so, in the situation where delegated prefix is
volatile (like PD with prefix-pool, as Green mentioned), how CPE should do?

- CPE sets preferred lifetime in RA with very small value (ex. 1 min)
  and advertises with a short period (20sec?).
- CPE has a stable storage and advertises an old prefix with pltime
  = 0, when CPE reboots accidentally and a delegated prefix is changed.

--
SHIRASAKI Yasuhiro @ NTT Communications
t: +81-3-6800-3262, f: +81-3-5365-2990