Subject: [Mip6] Reposting: Using the last Accepted Sequence Number in BA

From: "Ahmad Muhanna" <[email-masked]>
Date: Mon, 13 Nov 2006 15:15:55 -0600

Hi All,

After discussing this issue with some folks at IETF67, I am reposting it
one more time hoping that we will get consensus to address it
fundamentally.

The way that RFC3775 addresses this issue is by allowing HA to insert
the last accepted sequence number in the BA sequence number field, where
this field should have been populated by copying the sequence number
from the corresponding BU. However, some of the logics behind not fixing
this issue at the time was as follows:

*	MN has only one outstanding BU at a time.
*	Only happens in a rare scenario when the MN reboots,
*	IPsec is mandatory and its replay protection suffices in this
case.

On the other hand, I believe the proper way of handling this issue is to
copy the sequence number from the BU to the sequence number field in the
BA and at the same time to communicate the last accepted sequence number
via a new option "Last accepted sequence number" for example. In my
opinion, this issue becomes critical when using Proxy MIPv6, since the
Proxy agent will have many outstanding BUs at the a time and the
sequence number in the BA is used to find the matching BU.

Please let me know of your thoughts.

Many thanks in advance.

Regards,
Ahmad

> _____________________________________________ 
> From: 	Muhanna, Ahmad [RICH2:2Q30:EXCH]  
> Sent:	Thursday, May 18, 2006 9:27 AM
> To:	[email-masked]'
> Cc:	[email-masked]'; 'Charles E. Perkins';
> [email-masked]'; Khalil, Mohamed [RICH2:2S20:EXCH];
> 'Basavaraj Patil'; 'Gopal Dommety'
> Subject:	MIPv6: Using the last Accepted Sequence Number in BA
> 
> 
> Hi all,
> 
> In response to a Binding Update 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 Binding Acknowledgement with a status of 135 after
> inserting the last accepted sequence number received in the last valid
> Binding Update in the sequence number field (Different from the
> sequence number received in the outstanding BU)
> 
> According to MN processing of the Binding Acknowledgement 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.
> 
> Could you please comment on this and let me know if I am on the right
> track.
> Thanks.
> 
> Regards,
> Ahmad
> 
_______________________________________________
Mip6 mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/mip6

---

From: Vijay Devarapalli <[email-masked]>
Date: Sun, 26 Nov 2006 18:18:40 -0800

hi Ahmad,

section 11.7.1 of RFC 3775 says

    If the sending mobile node has
    no knowledge of the correct Sequence Number value, it may start at
    any value.  If the home agent rejects the value, it sends back a
    Binding Acknowledgement with a status code 135, and the last accepted
    sequence number in the Sequence Number field of the Binding
    Acknowledgement.  The mobile node MUST store this information and use
    the next Sequence Number value for the next Binding Update it sends.

>       According to MN processing of the Binding Acknowledgement 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.

the latter has been the intention always. I agree
that the text describing this is kind of "hidden"
in RFC 3775. :)

Vijay