Subject: [mobile-ip] Dialogue problem in some particular cases between the Mobile Node and the Correspondent Node

From: Frédéric Roudaut <[email-masked]>
Date: Fri, 13 Dec 2002 11:55:50 +0100

Hi,

perhaps I misinterpreted something but I think there could be a dialogue problem 
in some particular cases between the Mobile Node and the Correspondent Node.
Consider the 3 extracts hereafter:

9.5.2. Requests to Cache a Binding
...
The lifetime for the Binding Cache entry is initialized from the
Lifetime field specified in the Binding Update, although this
lifetime MAY be reduced by the node caching the binding; the lifetime
for the Binding Cache entry MUST NOT be greater than the Lifetime
value specified in the Binding Update. 

9.3.1. Receiving Packets with Home Address Destination Option
...
Packets containing a Home Address option MUST also be dropped if
there is no corresponding Binding Cache entry for the given home
address.  A corresponding Binding Cache entry MUST have the currently
registered care-of address equal to the source address of the packet.
These tests MUST NOT be done for packets that contain a Binding
Update and a Home Address option.   
If the packet is dropped due the above tests, the correspondent node
SHOULD send the Binding Error message as described in Section 9.3.3.
The Status field in this message should be set to 1 (unknown binding
for Home Address destination option).

9.5.5. Sending Binding Refresh Requests
...
If the sender knows that the Binding Cache entry is still in active
use, it MAY send a Binding Refresh Request message to the mobile node
in an attempt to avoid this overhead and latency due to deleting and
recreating the Binding Cache entry.  The Binding Refresh Request
message is sent in the same way as any packet addressed to the mobile
node (Section 9.3.2).

With a little exemple it will be easier to understand. We consider a 
Mobile Node which has already an entry in the binding cache of a 
Correspondent Node. Nevertheless for a specific reason the Lifetime in 
the binding cache entry is reduced from the Lifetime sent in the 
corresponding Binding Update. When the Lifetime will be expired, the 
Mobile Node will not know this if the Correspondent Node don't send a 
Binding error Message or a Binding Refresh Request. So because it is not 
an obligation to send one of these messages, all packets sent from the 
Mobile Node to the Correspondent Node with a home address destination 
option will be dropped.

So I think there should be a MUST in one of these extracts (especialy 
concerning the sending of the Binding Error) or you have to add a 
specific part for the specific case where the correspondent Node decide 
to reduce the Lifetime. If people implementing a Correspondent Node with 
this particular feature are not aware about this, this Node could 
rejected all packets sent during the end of the Lifetime periode. 

Moreover I noticed an editorial mistake in the format of the Home 
Address Option p41. Because the alignement requirement for the Home 
Address Option is 8n+6, you must have 4 Bytes between the field "Header 
Ext Len" of the Destination Options Header and the field "Option Type" 
in the Home Address Option. The option format written in draft 19 was 
the following  :

 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Next Header | Header Ext Len  |  Option Type  | Option Length |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                          Home Address                         +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Regards,

-- 
Frédéric ROUDAUT
IRISA-INRIA, Campus de Beaulieu, 35042 Rennes cedex, France
Tél: +33 (0) 2 99 84 71 44, Fax: +33 (0) 2 99 84 71 71