Subject: RE: [mobile-ip] Comments on Mobile IPv6 draft 14

From: "Venkata Jagana" <[email-masked]>
Date: Tue, 25 Sep 2001 18:08:58 -0700

>   Let us consider a scenario where MN moves from its home network 'A' to
>   foreign network 'B' and then to foreign network 'C'.
>
>   After moving from network 'A' to network 'B', MN should have registered
>   (i.e. BU sent)its primary CoA picked up at 'B' with the home agent at
> 'A'.
>   Now, the HA at 'A' has a binding cache entry marked home registration.
>
>   Next, the MN moves from 'B' to 'C', then, MN would send BU to the HA
>   at 'A' to request the change in cache entry with the new CoA just
> obtained
>   at 'C' and also to a home agent at 'B' to register its new CoA obtained
> at
>   'C' network. The registration with home agent at 'B' is required so
that
>   packets addressed to its old CoA at B will now be tunnelled to its new
>   CoA at 'C'. Effectively, the MN now has one home agent at 'A', which I
>   called 'Original Home - OH' (because that's where its home was) and
> another
>   home agent at 'B' which I called 'Foreign Home - FH' at 'B'.
>
>   Let us say that, after sometime, the MN came back from 'C' to 'B'
>   during its movement path and which means that MN can start reusing its
>   old COA at but before start using it there, it needs to deregister its
> CoA
>   at B with HA at 'B'; then sending a BU to its OH at 'A' with this CoA
>   at 'B'. Then, it will have to send a BU to HA at 'C' with the CoA at
'B'
>   to start tunnelling packets destined fro MN. In this case, the 'FH' is
>   effectively now moved 'B' to 'C'. In this case, it had to perform 3
> steps:
>   deregistration with 'B', registration with HA ('OH') at 'A' with CoA at
> 'B'
>   and registration with  HA ('FH') at 'C' with COA at 'B'.
>
>   Hope I made this clear without making it too complicated. So, my point
>   is that the draft didn't consider a scenario like this and hence never
>   talked about deregistration with home agent on the foreign networks the
>   MN visited.
>
           => I beleive that this is due to th fact that neither the data
structures
           => (Binding cache or BUL) nor the BUs distinguish between a
"foreign HA" or a
           => "real HA". So the section on deregistering when connecting to
the
           => Home network still applies to your scenario.

     Deregistering section, 9.4, applies to Home agent operation
     and it describes about what HA should do when deregistration
     (i.e. BU received) happens but what I am talking about is MN
     operation, sec 10.20 (MN returning home) and not HA. This scenario
     involves not just deregistration only but much more, sorry,
     I haven't made that very clear in my last mail.

     In a scenario, I have described here, MN should do the following
     things at a minimum:
          - deregister with home agent at 'B'
          - Binding update to home agent at 'A' to refresh its
            bcache entry with the CoA at 'B' now
          - registration with foreign home agent at 'C' to start
            tunnelling packets to CoA at 'B'

     At any time, a MN may have a single original/real Home Agent
     and single or multiple foreign Home Agents. At a given instance,
     the number of foreign home agents a MN may have, will depend upon
     how fast the MN is moving across the networks but it doesn't need to
     keep track of all those foreign home agents except for the last one.
     In a case where MN moves too quickly from one network to another,
     then it would have established registrations with each of those
     foreign home agents at the networks it visited earlier in order to
     have the packets tunnelled to its current CoA from the previous
     old CoA's.

     Section 10.20 simply talks about MN returning home (its original
     or real home) but it doesn't 'explicitly' talk about a MN moving
     back to a old network it just visited earlier and what MN
     should do (probably, I would consider this as a special case) and it
     is not covered at all in this section unless it is interpreted that
     it is left to the implementation, but I don't think that's a
     good idea to leave it that way.

Thanks,
Venkat

----------------------------------------------------------------
Venkata R Jagana
IBM Linux Technology Centre, Beaverton
[email-masked]
Tel: (503) 578 3430 T/L 775-3430

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From: "Peter Grimstrup (TED)" <[email-masked]>
Date: Wed, 26 Sep 2001 10:38:48 +0200

Hi Venkata,

If you for a moment view the MN as being CoA at 'B' (the first) visiting
network 'C' and then returning home to network 'B', the draft describes 
the procedure.
It might be a good idea though to add a bit in the draft explaining this.

However, I should like give another scenario almost similar to yours:
The MN returns to network 'B' but gets another (second) CoA at 'B'. In
this case, the "first CoA at 'B'" does not return home, and the 
deregistration at home agent at 'B' shouldn't be done.

Extending this scenario seems messy, but one should remember, that most
probably, the lifetime of "forwarding from a Previous Care-of Address"
is short.

Peter
--
Venkata Jagana wrote:
> ...