Subject: Re: [MOBILE-IP] Deregistration question...

From: [email-masked]
Date: Tue, 13 Jun 2000 11:39:57 -0500

I think the question was what happens if the deregistration HA  fails but the MN
would have
transmitted the gratuitous ARP before the HA begins the deregistration
process. Should the MN send another gratuitous ARP or am I missing
something ?

Cheers

Achari
---------------------- Forwarded by Umamaheswar Achari Kakinada/MW/US/3Com on
06/13/2000 05:44 PM ---------------------------

Steven Glass - Solaris Software <[email-masked]> on 06/13/2000
11:17:25 AM

Please respond to Steven Glass - Solaris Software <[email-masked]>

Sent by:  Steven Glass - Solaris Software <[email-masked]>

To:   [email-masked]
cc:    (Umamaheswar Achari Kakinada/MW/US/3Com)
Subject:  Re: [MOBILE-IP] Deregistration question...

> I was reading the latest draft revision of RFC2002 and I came across the
> part on the deregistration with HA.
>
> It was mentioned in the draft that the HA should transmit gratuitous ARP
> together with the (de)Registration Reply. The MN must transmit the
> gratuitous ARP before the HA begins the deregistration process.
>
> It was also mentioned later in the draft the if the HA rejects the
> (de)registration process, then no ARP processing is perform by the HA.
>
> Now, please correct me if I am wrong, if the MN sends the ARP packet before
> the deregistration process and the process fails, isn't there a possibility
> that some of the packets might be sent to this MN as their ARP tables might
> be updated with the gratutious ARP sent by the MN earlier?

    I suppose the ordering of most events is implimentation specific, but...

    The MN has to begins the deregistration process, as this is based on its
move detection.  The HA processes the deregistration requests, if it's
acceptable, removes the MN's binding, and sends a deregistration reply.  The
MN processes the deregistration reply, and if it's acceptable, sends its
address-claiming gratuitous arp.

     Yes, there is a non-zero amount of time between being removed from the
HA's binding, and reclaiming your address, but that's not really relavent.
One of the risks of roaming is not being where your traffic is going, and
happens everytime a MN roams, and many drafts specify FA's caching packets,
then delivering them to the new CoA upon getting binding updates.  To get a
clearer picture, try any that deal with fast handoff or route optimization.

                              Cheers,
                                  Steve

---

From: Steven Glass - Solaris Software <[email-masked]>
Date: Tue, 13 Jun 2000 14:04:27 -0400

> I think the question was what happens if the deregistration HA  fails but
> the MN would have

    Sorry - I've reread the relavent sections of d-i-m-rfc2002-bis-01.txt
(section  page 64 - 65 in particular) which does a lot to clarify and update
what 2002 says (said), so part of the ordering I said below is actually wrong
(!)  Specific to your question (in hopefully a more successful attempt to get
it right):

     Upon realizing it's on its home link:

        - The mobile node MUST reclaim it's address via gratuitous arp.  This
              updates the arp cache on the machines on the home link.
        - The MN generates a [de]registration request, and sends it to the HA.
        - The HA processes the [de]registration request.

            - If the HA rejects it, it generates a [de]registration reply with
                  the appropriate error, and sends it to the link address of
                  the MN.  The HA does NOT transmit any ARPs.

    In this way, the MN is receiving it's traffic despite the failed
[de]registration attempt since it has intercepted the traffic that would
otherwise have gone to the HA and into the tunnel.  There's no need for the MN
to retransmit that ARP, then again, there's no harm in it being retransmitting
when the MN is successfully deregistered, either.

    Sorry about [my addition to] the confusion!

    This is also probably where the disclaimer normally goes that this use of
ARP doesn't make the network less secure or chaotic than in the non-mobile
case; anyone can gratuitous arp an address if they so choose.

                              Cheers,
                                  Steve