Subject: [mobile-ip] regional registration MIPv4

From: Ayman A Abdel Hamid <[email-masked]>
Date: Tue, 9 Apr 2002 13:50:00 -0400 (EDT)

Hello,

I have  a question about internet draft 
Mobile IPv4 Regional Registration
draft-ietf-mobileip-reg-tunnel-06.txt

in section B.2 handling Binding Updates and B.3 regional registration

assume the following scenario

                            GFA
                            /
                           RFA3
                           / 
                         RFA0
                       /    \
                   RFA1     RFA2
                    /         \
                 FA1          FA2

the MH is handing off regionally from FA2 to FA1 (cross-over FA is RFA0),
then according to my understanding MH uses PFANE and FA1 sends a BU to FA2
with coa FA1. In this case FA2 relays the BU upwards to RFA2 with coa FA2,
which does the same and relays it to RFA0 with coa RFA2. now if this
message reaches RFA0  before the registration request from the new path,
RFA0 relays the BU to RFA3 with coa RFA0. in this case RFA0 and
maybe (RFA3,GFA) will mistakingly delete their visitor list entry for MH
and replace it with a binding cache entry. The same can happen if this
is a home registration which is actually a local handoff. 

Is my analysis right?

The draft specifies the following in section B.2
   "In the unlikely event that the crossover FA receives the Binding
   Update before it receives the Registration Request, it doesn't
   know that it is the crossover FA yet, and therefore relays the
   Binding Update to the next Foreign Agent.  When the crossover FA
   later receives the Registration Request, it will know that it is
   the crossover FA, and will send a Binding Acknowledge message to
   the mobile node (via the old route).  The foreign agents above the
   crossover FA in the hierarchy that also got the Binding Update will
   see that the Binding Update does not supply any new care-of address
   information.  so they and will ignore the Binding Update."

 The condition that "the coa supplied by the BU from child RFA to
father RFA is the same as the coa stored in the visitor list entry"
is satisfied for all RFAs in the old path?  

and later in B.3
   "The Previous Foreign Agent Notification Extension, Binding Updates
   and Binding Acknowledge messages are used for Regional Registrations
   in the same way as for Home Registrations."

so the draft is stating that the handling is the same whether it is a home
or regional registration 
although the processing is OK for the Home registration (even if RFAs
replace the visitor list entries with binding caches, the MH is renewing
his home binding anyway) , the same processing is not applicable to
regional registration (if my analysis is right).

Am i missing something? 

regards,