Subject: [mobile-ip] Improvement in Proxy DAD functionality for Mobility Support in IPv6

From: "Krishna Kumar" <[email-masked]>
Date: Mon, 20 Aug 2001 11:06:32 -0700

Hi all,

I am one of the contributors to the Mobile IP implementation on Linux,
along with the Main developers -  the HUT Team. While examining
the working of Proxy DAD, I would like to propose an improvement
in this functionality, which is not addressed in the draft.

Section 9.2 of the draft says that when the MN requests the HA to no
longer serve as it's HA (returns home) :

"In addition, the home agent MUST stop intercepting packets on the
mobile node's home link addressed to the mobile node (Section 9.3)."...

I feel this step should also apply for the HA when the binding cache
entry expires.

My reasoning behind this is :

1. The HA does not need to listen to expired entry's solicited multicast
   addresses after it's expiry. This way the list of multicast addresses
   doesn't become too large to manage on the HA. Basically if the HA is
   up for days/months/years and 100's (or more, futuristically) of MN's
   have moved from the Home Agent network during that time (and not
   returned to the HA but have shutdown or stopped using mobility), then
   the list of addresses in the multicast list can become very large.
   Searching, operating, adding or deleting an entry in this big list can
   take increasing times, as the uptime of the HA increases, leading to
   a performance hit.

2. If the MN goes to a foreign network and is shutdown or stops using the
   mobile service, the HA would still listen to all the MC addresses of
   each of these MN's home addresses. Then the HA would process the
   neighbor solicitation, and go through the binding cache as the spec
   says to see if a binding exists, and finds nothing.

   Basically we are doing a lot of processing when it is not necessary. The
   HA is not even serving as the HA for this MN if the entry has expired
   and there is no good reason to keep listening to the MC address.

3. From an implementation point (please bear with me!), another problem
   happens if the implementation of mobility is by using a loadable module.
   If the mobility module were to be 'unloaded' on the HA after the HA
   served many MN's (which moved to foreign networks and 'expired'), then
   potentially the HA would be listening to many multicast solicited
   addresses.

   So removing mobility support on the HA would not restore this system to
   it's ORIGINAL state before the module was loaded.

I would like to suggest that the draft be modified to say that when an
entry in the binding cache expires, the home agent MUST stop
intercepting packets on the mobile node's home link addressed to
the mobile node.

I would appreciate any comments on this issue.

Thanks,

- KK

Krishna Kumar
(503) 578-3602
[email-masked]

---

From: Francis Dupont <[email-masked]>
Date: Tue, 21 Aug 2001 18:16:29 +0200

=> I fully agree. I believe this was already in the text but between lines...

Regards

[email-masked]

PS: the HA should flush the whole context too, including keys.

---

From: "Charles E. Perkins" <[email-masked]>
Date: Tue, 21 Aug 2001 09:25:00 -0700

Hello Francis,

> => I fully agree. I believe this was already in the text but between lines...

Right.

> PS: the HA should flush the whole context too, including keys.

This would be bad for mobile nodes that want to sleep but use the same
security association when they wake up a few hours later.

Regards,
Charlie P.

---

From: Francis Dupont <[email-masked]>
Date: Wed, 22 Aug 2001 12:29:05 +0200

=> are HA supposed to have infinite (2^64 * sizeof(context)) memory?
BTW if keys have their own lifetime there is no issue (i.e. add
this as a requirement for key management with all the little details
like keys expire before the binding, etc).

Regards