Subject: [mobile-ip] iessue 238: Send BAs via home to avoid special case

From: Pekka Savola <[email-masked]>
Date: Sat, 25 Jan 2003 07:15:13 +0200 (EET)

The issue 238:
=====
Pekka Savola writes:

   to the Source Address.  Unlike the treatment of regular packets, this
   addressing procedure does not use information from the Binding Cache.
   However, a routing header is needed in some cases.  If the Source
   Address is the home address of the mobile node, i.e., the Binding
   Update did not contain a Home Address destination option, then the
   Binding Acknowledgement MUST be sent to that address, and the routing
   header MUST NOT be used.  Otherwise, the Binding Acknowledgement MUST
   be sent using a type 2 routing header which contains the mobile
   node's home address.

==> the latter case seems strange.  Consider e.g. a BU with HAO option for
which CN replies with BA expired nonces (or something like that), 
what use is it to use routing header to send that back to the MN?  
Rather, it could be much more robust to
just by default push everything to the home address, and have them reverse
tunneled to the MN.

------------

Jari Arkko writes: I think we need them to go directly to the
sender. Otherwise, after a movement, it is very hard to see an error
response. Or?
=====

==>

My belief is that, _always_, the first thing after the movement, MN must 
send a BU to the home agent, updating its location.

So, this would only be a problem if the network latency between MN->HA is 
bigger than MN->CN->HA.

The optimization is arguably useful if MN is a long way from home, 
communicating with a CN which is close.  But in that case, I think CN is 
also about equally far off..

A lot of things break, I suspect, if HA does not have the new location 
updated..

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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From: Jari Arkko <[email-masked]>
Date: Sun, 26 Jan 2003 02:51:41 +0200

> A lot of things break, I suspect, if HA does not have the new location 

Yes.

What you propose would work well for the CNs, as we require a registration
in place before you can send BUs to them (and due to RR that would
be necessary anyway).

However, what Section 9.5.4 says is also used by home agents, see
Section 10.3.1. And for home agents, we do indeed have a problem;
this is the same BU that was supposed to be done already in order
for us to send the reply to the right place.

I agree that it would be cleaner to send always to the home address,
but I don't see a way around the above. Of course we could separate
the cases for CNs and HAs, but I think it would just introduce
additional special casing without removing the original problem
completely.

So my suggestion is to leave this as is.

Jari

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From: Pekka Savola <[email-masked]>
Date: Sun, 26 Jan 2003 15:33:58 +0200 (EET)

> additional special casing without removing the original problem

I can live with this, and agree that these two should probably not be 
separated.

Another option entirely would be to send BA's to the source address,
always -- regardless of the HAO if present.  That would seem rather a
simple operation to me.  (However, this might vary a bit depending on how
implementations process/replace source address with HAO.)

What worries me here is using this sending procedure for BU's that failed,
ie.  those BA's that have status code >= 128 (ie. the home address has not
been accepted yet, but we send a reply there anyway).  But I don't see
much use in separating these cases, as that would only create more
complexity and not uniformity.