Subject: [mobile-ip] FMIPv6 prehandover signaling timing (was Re: [Seamoby] CARD - FMIPv6 protocol interworking)

From: "James Kempf" <[email-masked]>
Date: Fri, 20 Dec 2002 14:04:04 -0800

Rajeev,

(discussion forwarded from the Seamboy List)

> > There has been a discussion in the MIP group about whether the FMIPv6
> > prehandover signaling should be completely decoupled from handover, but the
> > discussion has not reached any clear conclusion. One issue is whether
decoupling
> >
>
> On the [mobile ip] mailing list, I saw many folks favoring this "advance
signaling"
>
> prior toAtlanta IETF. During the fmip presentation at Atlanta on this issue, I
> didn't hear any objections. I am willing to say that this is recommended in
the
> spec,
> while the MN MAY also do it during handover if it so wishes (please see the
ATL
> slides).
>
> > the signaling would also decouple any signaling between the mobile's current
> > access router and other access routers (i.e. HI/HAck). If no signaling
occurs
> > between access routers when the FMIPv6 signaling occurs (that is, it is for
> > information only), then that would be the equivalent of CARD. If signaling
does
> > occur, perhaps to pre-configure a care of address on the new subnet, then it
> > would be different.
>
> The implication is that HI/HAck would take place upon receiving FBU. It
probably
> does not make sense to create and manage handover state without knowledge of
> when exactly the MN is undergoing handover (again, see the ATL slides).
>

There is an issue with not coupling the prehandover signaling to the handover.
The issue is that if the intent is to do anticipated care of address
configuration, as has been the case in the past, there would have to be a
HI/HAck exchanged prior to the handover in order for the address to be
confirmed. If the HI/HAck is only done after handover, then address
preconfiguration cannot be reliably done.

If we want to continue to support anticipated care of address configuration and
decouple the signaling, the result would have the MN with care of addresses
reserved in multiple subnets around the current one, based on link information
about the quality of the wireless signal. It would be up to the MN to figure out
which subnets where it should reserve an address. While IPv6 addresses aren't as
precious as IPv4, this will still result in some amount of resource consumption
(an IPv6 care of address) that the MN may never use.

            jak

---

From: Rajeev Koodli <[email-masked]>
Date: Fri, 20 Dec 2002 18:29:28 -0800

> preconfiguration cannot be reliably done.

Good point. The purpose of prehandover signaling is twofold. First, learn the
MAC address of the router prior to moving in order to be able to send
packets immediately upon establishing a new link. Second, learn the new router
prefix information in order to be able to configure a prospective new CoA.
The latter cannot be confirmed without HI/HAck. So, with the new changes,
the MN knows about the prefix and hence a new CoA it could use, but it needs
to confirm that upon attaching to new AR. It did such a thing in the current spec
anyway when it didn't get an FBack (by sending FNA). I think we can make sending
something like FNA (or an option) a default.
Finally, not confirming new CoA won't be an issue for FBU, since it binds previous
CoA with new AR's address.

-Rajeev

ps. I will be away next couple of weeks.