Subject: [Mip6] [issue101] A problem in setting SQN in the BA with status 135 which may cause Collision

From: Ahmad Muhanna <[email-masked]>
Date: Tue, 15 May 2007 04:29:20 +0000

New submission from Ahmad Muhanna <[email-masked]>:

In response to a BU which contains an out of range sequence number, as per 
sections 9.5.1 and 11.7.1, the CN or HA is allowed to send a BA with a status 
of 135 after inserting the last accepted sequence number received in the last 
valid BU in the sequence number field (Different from the sequence number 
received in the outstanding BU)

According to MN processing of the BA as specified under section 11.7.3., the 
MN will silently discard the received BA rather than picking the last accepted 
sequence number and then generate a new sequence number. 

I think the intention was to allow the HA or CN to communicate back to the MN 
the last accepted sequence number, however, we are breaking the protocol by 
using this mechanism.

This issue becomes critical in the case of PMIPv6 since the PMIP client would 
have thousands of outstanding P-BU and the recieved P-BA most probably will 
collide with another outstanding P-BU causing the PMIP client to drop the P-BA 
and contuinue to styay out of sync with the LMA/HA.

Solution:
I believe the most straightforward solution for this issue is to enable the 
original intention opf RFC3775. i.e. by communicating back the last successful 
sequenmce number in a option:

Las Valid Sequence Number Mobility Option:
6.2.x.  Last Valid Sequence Number

   The Last Valid Sequence Number option has an alignment requirement of 2n.
   Its format is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |   Type=TBD    |   Length = 2  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Last Valid Sequence Number  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Last Valid Sequence Number option is only valid in a BA, sent from the 
mobile node's home agent in reply to a home registration, with a status of 
135. The Last Valid Sequence Number is the last sequence number that the Home 
Agent received in the last successful Binding Update for the specified 
session. In case the Home Agent receives a Binding Update with a sequence 
number outside the valid sequence number range, the Home Agent sends a BA with 
a status of 135. HA must copy the sequence number from the BU into the 
sequence number field of the BA. HA must include the last Valid Sequence 
Number into the Last valid Sequence Number Mobility option.

----------
category: Technical
draft: RFC3775
messages: 354
nosy: ahmad, bpatil, charles.perkins, sri, vijay
priority: Must fix
status: Pending
title: A problem in setting SQN in the BA with status 135 which may cause Collision

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