Subject: [mobile-ip] MIPv6 "granted lifetime" problem

From: Ra Chen <[email-masked]>
Date: Mon, 9 Jul 2001 15:23:40 +0800

Hi all:

In our attempt to implement Mobile IPv6,
we encounter the following problem.

In draft-ietf-mobileip-ipv6-14.txt, Sec. 10.13,
it's described that the reamining lifetime should be
         max((L_remain - (L_update - L_ack)), 0)

Here is an implementation problem.
To do the calculation, L_ack and L_update must be a pair.
That is, the BU of L_update and the BA of L_ack
must have identical sequence number.

However, according to Sec. 4.6, 
         for multiple Binding Updates sent to the same destination
         address, the Binding Update List contains only the most recent
         Binding Update (i.e., with the greatest Sequence Number value)
         sent to that destination.  
Now if the BA for the initial BU is received after a BU retransmission,
the mobile node has no information about L_update,
which has been overwritten by the BU retransmission,
and doing the calculation correctly is impossible.

To fully comply with the draft,
the mobile node has to record L_update for ALL its un-Acked BU,
in order to use the matching L_update once a BA is received.
This seems against the spirit of Sec.4.6.

Best Regards

==================================
Ra Chen
Siemens Telecommunication Systems Ltd.
R&D Engineer
E-mail: [email-masked]
Tel: 886-2-2518-6539
Fax: 886-2-2505-3866
==================================

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From: Keiichi SHIMA <[email-masked]>
Date: Mon, 09 Jul 2001 17:28:13 +0900

Hi,

> and doing the calculation correctly is impossible.

I have met the same problem. The problem is more serious when
de-registrating I think. 

0. MN sends BU with seqno n.
1. MN resends BU with seq n+1 bacause BA with seq n did not come
   in a BINDACK_TIMEOUT time.
2. HA receives BU with seq n. de-register, send back an BA with
   seqno n to MN.
3. MN receives BA with seq n but MN silently discards it because
   the seqno is not the same to the BU's seqno MN sent last time.
4. HA receives BU with seqno n+1. but discards it and send BA to MN
   with errcode NOT_A_HOMEAGENT

If we don't increment seqno when retransmitting BU, are there any
vulnerabilities? If seqno remains same until matching BA received,
those problem will not occur. and it is easier than holding all
sending BUs in a BU list.

---
Keiichi SHIMA <[email-masked]>
Internet Initiative Japan Inc.

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From: Vijay Devarapalli <[email-masked]>
Date: Tue, 10 Jul 2001 10:46:35 -0700

hi,

comments below

> Now if the BA for the initial BU is received after a BU

this BA is dropped. only the BA with the sequence number matching
the most recent BU is accepted.

so you need to store the state only for the most recent BU sent.

Vijay