Subject: [mobile-ip] Sub: Identifying link changes

From: [email-masked]
Date: Wed, 19 Jun 2002 09:54:43 +0530

> > Now the selected router turns to Host, by advertising with router
lifetime
> > set to Zero. But the router is still advertising the prefixes for
> > autoconfiguration (not acting as default router).
> > MN selects the next default router in the same link. But MN is unaware
a
> > router change or network change in the same link or a different link.
So it
> > forms primary care-of address and registers with Previous HA (Smooth
> > Handoff). In this case, the BU with 'D' bit set is sent to HA in the
same
> > link.

Samita wrote :

> How do you mean by "previous" HA ? Why does it need to change HA ?
> Your scenario does not describe that. How do you mean by "HA in the
> same link" ?

Probably, I may not have explained it properly in my previous mail.
                __
  --           |MN|                 --
 |R1|----------------------------- |R2|
  --       (Foreign Link)  |         --
3ffe:1::0                  --      2ffe:1::0
3ffe:2::0             |HA|    2ffe:2::0
                           --

Assume that MN has selected R1, has default router which advertises the
prefixes,
3ffe:1::0, 3ffe:2::0. Now, this has changed to Host. So, MN is switching to
another default router on the same link which is advertising with
2ffe:1::0,
2ffe:2::0. As far as MN is concerned, it is unaware whether it is a router
change
from the same link or from a different link.

MN forms primary care-of address and registers with HA in its Home link
(which performs DAD on the Home link for its Home addresses, not shown
in the diagram).

Since, the prefixes are different there is a network change.  Hence MN will
send
a BU to previous network HA (which is in our case, nothing but the HA in
the same
link as the MN is currently in).

My question is, can MN avoid sending BU to HA when there is no link change?
If so, how to identify the link changes?

> The above scenario does not seem to be valid.
> DAD is performed on the home-address by the home-agent on the home-link.
The
> assumption is home-link is separate from the foreign link.

Is DAD, not performed by the HA in the foreign link?

Srinivasan

---

From: Jari Arkko <[email-masked]>
Date: Wed, 19 Jun 2002 19:45:23 +0300

>  |R1|----------------------------- |R2|

Ah, OK, now I see...

> If so, how to identify the link changes?

I'm still not sure there's a problem. Let's discuss two cases:

1. R1 turns into a real host. In other words, it no longer sends
    any Router Advertisements. It will therefore not answer any Binding
    Updates or defend anyone's addresses either.

    In this case the end result is similar to the case when R1 would
    simply die. The old CoA becomes unavailable. The MN would use a new
    one. If there were packets on their way to R1 from the CNs, those
    will be dropped.

2. R1 declares that it is no longer a default router. It will still
    be a router, and send Router Advertisements.

    Is this harmful? Only if (a) R1 performs DAD and (b) MN answers
    the DAD. But how can we get into such a situation? R1 will of
    course perform DAD if it still works as a home agent, and the
    Binding Update has the 'D' bit on. But why would the MN answer
    DAD? If the MN believes it is on foreign link, why would it
    respond to a DAD on an old CoA?

    Come to think of it, I'm not even sure why the MN would
    respond to NS on its own HoA before it has determined that
    it is on the home link (11.6.7).

In conclusion I think we should state the following in the
specification. The MN SHOULD NOT respond to NS on its home
address until it has determined that it is on the home link
and has successfully deregistered its binding from the home
agent.

Jari