Subject: Re: DHCPv6 address model proposal...

From: Thomas Narten <[email-masked]>
Date: Fri, 22 Sep 2000 08:07:35 -0400

Ted,

Sorry to be so long in following up, but it sounds like we're
basically in sync, except that terminology threw things off. Cool.

One thing in your posting though has me thinking.

> > In the mobile IP scenario, you will likely have *two* global
> > addresses. One for your home address, and a temporary care of
> > address. Both will need to be global in order for arbitrary sites to
> > send packets to them. Note, however, that in this case the client will
> > be interacting with two different DHCP servers in two different
> > contexts. The care-of address comes from the local site that is being
> > visited, the home address comes from the home site. So it's not clear
> > you need to identity associations separately here (though you might
> > want to), since two servers are involved and that is enough to
> > distinguish which addresses one is talking about (i.e., care-of
> > vs. home).

> Right.   So you have two identity associations.

Then later:

> > I hope not. If a client moves to a new link/subnet, it should just
> > request that the DHCP server "give me the set of addresses that I'm
> > supposed to have on the new link I just joined".

> This sounds like the client is making a different request depending on
> it's perception of the status of the link.  Is there any particular
> reason why the client can't just say "please renew this IA" and have
> the server say "okay, because you're on a new link, here are your new
> addresses?"  I.e., the client asks the same question, rather than
> having to be clever and decide which question to ask?   The client
> might be stimulated to ask for an early renewal because it noticed
> that the router advertisements it was seeing had changed, but I don't
> think it needs to explicitly tell the server "hey, I'm on a new
> subnet."

My assumption has been that when a node moves to a new link, it would
ask for addresses using the *same* IA. I.e., the client doesn't want
to know that it is on a new link and therefore needs to use a
different IA when asking for new addresses (but that might be in
conflict with your first point above). However, thinking about it, a
mobile client *will* need to know its on a new link, as all sorts of
things change for it if it moves to a new link (i.e, it needs a new
first-hop router). So having it send a different IA when moving
probably probably isn't a big deal either. But is it really necessary
or desirable?

Thoughts?

Thomas

---

From: Ted Lemon <[email-masked]>
Date: Fri, 22 Sep 2000 10:38:25 -0700

> However, thinking about it, a mobile client *will* need to know its
> on a new link, as all sorts of things change for it if it moves to a
> new link (i.e, it needs a new first-hop router). So having it send a
> different IA when moving probably probably isn't a big deal
> either. But is it really necessary or desirable?

Yes, the highly-mobile client has to notice the link transition.   No,
it doesn't need to use a different IA on each link - indeed, it should
not.   The IA that notices link state changes is for its care-of
address.   The second IA is for its home address, if it's using DHCP
to allocate that.

			       _MelloN_