Subject: RE: Fast Handovers for MIPv6 - new Draft -comments BU+SA

From: George Tsirtsis <[email-masked]>
Date: Fri, 9 Feb 2001 08:13:07 -0500

-----Original Message-----
From: Erik Anderlind [mailto:[email-masked]]
Sent: Wednesday, February 07, 2001 10:36 PM
To: George Tsirtsis; IP Routing for Wireless/Mobile Hosts (mobile-ip)
Subject: Fast Handovers for MIPv6 - new Draft -comments BU+SA

Hi George,
Comment on Draft

page 3:
  The mobile node sends a
   Binding Update using its newly formed COA as the last message before
   it executes the handover.  The mobile node then receives a Binding
   Acknowledgement either through the oldAR or the newAR indicating that
   the binding was complete. 
Why allow the BU-ACK to be sent to either the old or the new address? 
I think the text should say: The BU-ACK is received on the COA used in
the BU
message. 

GT> That is correct but...the above statement only says that this message
may be delivered *by way* of newAR or directly from the oldAR. We expect the
oldAR to send it the BUACK both ways so we ensure that the message will be
received by the mobile. Ideally we would like to deliver the BUACK to the MN
before it moves but this can not be certain due to the degrading old link...

Security considerations:
THe assumption seems to be that the oldAR and newAR share the same
security association,
or the scheme is flawed.

GT> Yes, the Fast Handover we describe can only be supported if there is an
SA between old and newAR. We also assume an SA between MN and oldAR.

There seems to be a need for establishing new direct SAa in the
following scenario:

Start: Mobile and AP_1 share an SA.

GT> I assume that by AP you actually mean Access Routers...in which case
yes.

Step 1: Mobile initiates Handover to AP_2. 
(Draft states it is sufficient to have the following SAs: MS<->AP_1,
AP_1<->AP_2)

GT> Yes.

Step 3: Mobile initiates handover from AP_2 to AP_3.
THe draft does not require establishment of an SA betwen MS and AP_2, so
there 
seems to be a transitive association 
{MS<->AP_1, AP_1<->AP_2, AP2<->AP_3} -> can verify MS <-> AP_3.

The draft should state the mobile MUST negotiate an SA with AP_2 before
it 
can perform a handoff to AP_3.

GT> Yes, that is what we assume. SA between MN and AP_2 (or better AR_2) IS
required but only when the MN handsoffs to AR_3...it is NOT, however,
required for the MN to move from AR_1 to AR_2.

George