Subject: [Mip6] Comments on draft-montavont-mobileip-multihoming-pb-statement-00.txt

From: "James Kempf" <[email-masked]>
Date: Fri, 7 Nov 2003 11:59:03 -0800

Though I had been looking forward to reading it, the draft was a bit
disappointing to me. The bottom line seems to be "there's a problem because
MIPv6 doesn't allow binding multiple CoAs to an HoA" but I didn't find any
real motivation as to why that is a problem. There's a few words in the
introduction about users being able to use various types of interfaces, but
the connection between these very high level desirables and the fairly low
level constraint imposed by the current MIPv6 design was not readily obvious
to me. The reasoning also seems to be circular, as if the solution - binding
multiple CoAs to an HoA - had already been decided upon.

Section 1, paragraph 2 seems to provide the high level motivation. It is
asserted that "users should thus be able to select the most appropriate set
of inetwork interface(s) depending on the visiting network environment..."
But I don't find this to be a problem with my new T40P IBM Thinkpad. It's
got two interfaces, 802.11a and 802.11b, and I can set up profiles that will
select one or the other depending on the SSID. Generalizing, interface
selection can be handled in this manner with Mobile IP too, so it is unclear
why multiple CoA binding to one HoA would help solve the problem. Secondly,
it is asserted that "users should be able to select the most appropriate
interface per communication type" and an example of using a different
interface for UDP and TCP is cited. Most users don't know and shouldn't care
whether TCP or UDP is used (for that matter, SCTP or
DCCP might be the protocol) so this example doesn't sound very motivating
either.

Section 3 on benefits seems a good start, but I think more is needed. In
particular, tying this down with a technical analysis of the problem might
be useful.

The taxonomy in Section 4 was only marginally useful, since I didn't find it
connected to any problem statement. I didn't understand what the definition
of an IPv6 Link is. It seems to mean a wireless local link connection, but
this was unclear since such a connection doesn't necessarily have to use
IPv6. Figure 1 and the discussion don't seem to consider the case where the
mobile node has multiple interface cards that are connected through the same
radio link, like having multiple 802.11b cards.

Section 5 on Open Issues again seems to have a presumed assumption of a
solution, namely multiple CoA bound to one HoA. It really doesn't consider
the problems that such a solution could solve. There are a few
considerations brought up at the end of the section about issues not related
to the presumed solution, e.g. multiple HoA management, flow redirection and
management, etc.

Finally, there is an issue with the presumed solution in that security on
MIPv6 signaling between the HA and MN is done using an IPsec SA and IPsec
typically ties the SA to one address on both sides. The same issue arises
with SCTP, and I believe some work is currently going on to solve it.

            jak

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