Subject: [mobile-ip] section 11.3.6 MN requirement, needs additional clarification?

From: "Ed Remmell" <[email-masked]>
Date: Thu, 3 Apr 2003 14:13:08 -0800

I ran across an optional "MAY" requirement for the MN that I almost didn't
implement because it seemed unnecessary, and then I independently (i.e.
w/out this requirement in mind) came up with a reasonable race condition
that would cause the same symptoms, and since the end result in this
scenario causes the MN to remove a perfectly good BUL entry, I changed my
mind that this is a fairly important requirement that I need to implement
(perhaps a little differently - I'm using hysteresis since I'm not too
concerned about the "spoofing" scenario that the MIPv6 specification
mentions). Here is the section 11.3.6 requirement:

"   Otherwise, if the message Status field was 1 (unknown binding for
   Home Address destination option), the mobile node should perform one
   of the following two actions:

   o  If the mobile node has recent upper layer progress information
      that indicates communications with the correspondent node are
      progressing, it MAY ignore the message.  This can be done in order
      to limit the damage that spoofed Binding Error messages can cause
      to ongoing communications."

The race condition is:
If a MN detects movement very quickly, and quickly updates the CN with its
new care-of address on a new link (i.e. executes a fast handover taking < 60
msec), it is quite possible (since packets the MN sends on the old and new
links involve different access routers, and can therefore take different
paths through the network, also the access routers themselves can introduce
different delays) that packets that the MN sent to that CN on the old link
(with the old care-of address) arrive out-of-sequence at the CN after the BU
with the new care-of address sent by the MN on the new link is accepted by
the CN. This will cause the CN to respond with the BE status=1 (unknown
binding for Home Address destination option) when it receives and processes
out-of-sequence those old packets sent by the MN on the old link. If the
above requirement is not implemented in some fashion, this results in the MN
removing a perfectly good BUL entry that it has just successfully updated
with its new care-of address.

How I'm implementing this requirement is I'm having the MN insert a little
hysteresis between the WaitA (wait for BA from CN after creating new binding
or updating care-of address of existing binding) and the Bound states, and
during this period of time the MN ignores this type of BE message from the
CN.

Thanks.
- Ed Remmell
Elmic Systems, USA

---

From: "Ed Remmell" <[email-masked]>
Date: Thu, 3 Apr 2003 14:34:15 -0800

Ahhh, never mind. Upon further consideration, perhaps this isn't really an
issue because the CN will send the BE to the old care-of address on the old
link, and the MN is no longer there? What about interaction with forwarding
from old care-of address (not in the base spec)? Or, there is the
requirement that the MN needs to support receiving packets on its old
primary CoA (to smooth handovers), but I think that is a different scenario.
OK, I guess this was a false alarm.

Thanks.
- Ed

> -----Original Message-----
> From: [email-masked]
> [mailto:[email-masked]]On Behalf Of Ed Remmell
> Sent: Thursday, April 03, 2003 2:13 PM
> To: Mobile IPv6 mailling list
> Subject: [mobile-ip] section 11.3.6 MN requirement, needs additional
> clarification?
>
>