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

From: [email-masked]
Date: Tue, 18 Jun 2002 18:07:32 +0530

> First, is this a legal or useful scenario?

Let me explain the scenario clearly:

MN is in a foreign network, which has 2 default routers (which are Home
Agents also). Each default router, advertises 2 global unicast address
prefixes. Hence there are 4 global networks on a single link. MN has
selected one default router on that link and registered its primary CoA.

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.

Now, when HA performs DAD,  DAD fails, since MN defends the addres. MN is
notified of DAD failure. So, MN deletes the entry from the BUL assuming to
go without smooth handoff. But the address configured by MN are still
valid. Hence, MN can receive the packets sent by any nodes directly in that
link (Indirectly Smooth handoff is taken care).
> Since the MN is still on the link, it would be receiving packets destined
to it even at the old care-of
> address.

I fully agree with this.

> But if this is a useful scenarion, then the MN could leave the D bit to
zero.
> There is no text in the current draft, however, to describe this
particular
> reason for leaving it to zero.

When u set D bit to zero, HA will start perform proxy for a MN which is
also on the same link. IMHO, this is incorrect.

Is there any other way of identifying the link changes in an IPv6 network,
so that MN can avoid sending a BU to Previous HA when there is no link
change.

Srinivasan.D,

---

From: Samita Chakrabarti <[email-masked]>
Date: Tue, 18 Jun 2002 13:33:03 -0700 (PDT)

> selected one default router on that link and registered its primary CoA.

OK. This is regular IPv6 protocol. Here MN is using one of it's auto-conf
addresses as primary COA in the foreign network.

> Handoff). In this case, the BU with 'D' bit set is sent to HA in the same

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" ?

> to it even at the old care-of

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.

-Samita

---

From: Samita Chakrabarti <[email-masked]>
Date: Wed, 19 Jun 2002 16:22:45 -0700 (PDT)

>
> 
> 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?
> 

As per section 11.4 (movement detection) when a MN changes it's default-router
and acquire a new primary COA, it indicates that MN may send a binding update.

If the previous default router still stays as a router, MN would still continue
to receive packets from CN. If that router dies or becomes a non-router, then
MN will have to send BU to stay connected.

 While MN is on the link, it
should receive both prefixes from both the routers and it already keeps track
of list of COAs and default routers on the network. But it selects one of them
as it's primary default router and it also selects a corresponding COA.
So, when it switches to the backup router it should know that there is no
change in link has happened. 

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

No, assuming your HA link is separate than the foreign link.

-Samita