Subject: [Mip6] More comments on draft-ietf-mip6-dsmip-problem.00.txt

From: Alexandru Petrescu <[email-masked]>
Date: Mon, 24 Oct 2005 14:34:43 +0200

Dears, here are more comments on draft-ietf-mip6-dsmip-problem.00.txt

Overall, the document tries to motivate the need for v4 enhancements to
MIP6 and v6 enhancements to MIP4.  It achieves that mainly by using
'efficiency' arguments - it claims it's not efficient to run both MIP4
and MIP6 on a single MN.

'Efficiency' is something difficult to describe when so little context:
what's efficient for some is total waste for some other.  Argumenting
over efficiency is usually further supported with analysis data, and I
was expecting to see some tables with measurements, that would say that
a small PDA is very slow when running both MIP4 and MIP6, or similar.
These measurements are not provided.  From implementation experience, I
personally don't see a PDA being slowed because both MIP4 and MIP6 run;
that PDA doesn't run any faster when only MIP4 or only MIP6 runs.

The only quantified argument provided is that it's bad for MN to send
two messages whenever handover (a RegReq and a BU).  But this
immediately bears the question: why it's bad?  Is it taking too long?
With respect to what?

It also invites to counter-argument that an MN receiving FA
Advertisements does not necessarily receive RAs simultaneously, i.e. a
change in v4 CoA is not necessarily a change in v6 CoA.  This
'decoupled' change happens when the access network is v4 and v6 access
is through a tunnel.  So it is not true that every change in v4 CoA
demands both RegReq and v6 BU.

So, overall I think the draft has a valuable conclusion (motivate v6
enhancements to MIP4 and viceversa) but has a useless motivation.

For example, assuming that running both MIP4 and MIP6 is not
inefficient, it is possible to have a MIP4/MIP6 DS MN that connects to a
v4 access network, run the full MIP6, run the NAT Traversal part of
MIP4, and obtain an implementation that does not need neither v4
protocolar enhancements to MIP6 nor v6 protocolar enhancements to MIP4.

Alex

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