Subject: [mobile-ip] Cisco mobile networks move detection question

From: John Wells <[email-masked]>
Date: 08 May 2002 17:55:19 -0400

Hi all,

I have a question on Cisco's v4 mobile network implementation's move
detection algorithm.  If a Cisco mobile router is registered with one
foreign agent and hears an advertisement from another foreign agent, it
automatically registers with the new foreign agent and uses the new
address, as far as I can tell.  This would seem to contradict the Mobile
IP RFC, which provides for two move detection algorithms (RFC 2002, s
2.4.2):  one based on router advertisement expirations, the other based
on the prefix-length extension.  Cisco routers do not broadcast
prefix-length extensions, so the latter is not possible.

It would seem that Cisco's algorithm might result in oscillation in the
case of two foreign agents on the same subnet, for example in wireless
scenarios.  Any thoughts?

Thanks,
John

-- 
John Wells, Virginia Tech Networking Lab
(tel) +1 540 231-8347 (web) http://www.ee.vt.edu/~wells

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From: kleung <[email-masked]>
Date: Thu, 09 May 2002 08:05:00 -0700

Hi John.

> prefix-length extensions, so the latter is not possible.

Cisco routers can append prefix-length extension to agent advertisements.
It is enabled on the interface by "ip mobile prefix-length" command.

> case of two foreign agents on the same subnet, for example in wireless

The mobile router will not oscillate between 2 FAs on same subnet.

Kent