Subject: RE: [netlmm] Multiple Interface support in PMIPv6

From: "Mohana Jeyatharan" <[email-masked]>
Date: Tue, 13 Nov 2007 15:53:25 +0800

Hi Vijay,

Thanks for posting your draft: analysis of multiple interface attachment
over PMIP. It is really good that you have analyzed all possible ways of
achieving multihoming in PMIP and I think it is always good to think in
this line when one considers possible techniques of achieving host
multihoming in PMIP domain.

I have some comments or feedback on this draft.
Your draft has primarily concentrated on a multi-prefix model and
analyzed the possible issues that may have to be dealt if the
multiprefix model is implemented as specified in PMIPv6-v7.

In section 3.1 where you have analyzed a horizontal hand-off scenario,
it seems you have identified that when interface identifier is not
available, the LMA may assign a different prefix if hand-off indicator
flag is set to "4" (meaning do not know the hand-off type). Also it is
mentioned that the hand-off type has to be known to MAG3 to get the
correct prefix allocated by LMA. But, IMO it seems the IF-ID given MN at
L2 attachment to MAG3 is sufficient to get the correct prefix allocated
at LMA. Is the hand-off state to be known by MAG3 important? Bcos, when
I read the draft, you have mentioned context transfer and AAA providing
informarion on hand-off state. I was thinking, since MAG3 does not know
IF-ID, MN giving it as you stated is sufficient. The hand-off state need
not be notified.  

I have another general query. From base draft v7, the general
understanding is that for horizontal hand-off, the prefix will be
allocated to new MAG based on matching the If-ID in PBU to the existing
IF-ID cache at LMA. The basic assumption for this to happen is that the
de-reg should not arrive before the hand-off PBU. If the de-reg arrives,
then there is a possibility a new prefix may be allocated. I am not sure
how the base spec will handle this? Any thoughts?

In section 3.1.2, to solve the same prefix to be assigned during
hand-off between interfaces (vertical hand-off), you have mentioned that
either If-ID, prefix or MAG address of the handed over interface needs
to be sent to get the correct prefix to be assigned. I thought this is
already covered in the base draft. Correct me if I am wrong. Pg. 26,
bullet 5 has a scenario, where during vertical hand-off the previous
interfaces's assigned prefix is sent in the PBU. I felt that this issue
is already covered. 

Now, in section 3.2, you have mentioned of achieveing multihoming using
a single prefix model. But, the question I have is, why should the
binding cache be such that the addresses are used to differentiate the
simultaneous bindings. Can't prefixes and some other interface specific
identifiers be used. Restricting to addresses means, that a flow
addressed to a single address cannot be traversed via all attchments of
a MN to PMIP.

Furthermore, I have another question on the multilink subnet issue you
have mentioned for a single prefix model. When MN sees the same prefix
via both interfaces it resembles a multi-link scenario. I perfectly
understand this. In a multi-link subnet scenario, to avoid duplicate
addresses being assigned, DAD may need to be done. And as you have
mentioned in the draft, in a point-to-point link model, neighbour
discovery cannot be run between two distinct point-to-point links. I
have some clarification on this. First of all, since each prefix on MN
interface is unique to a MN, a duplicate address configuration as in the
case of general multi-link subnets does not arise here as long as the MN
is notified not to respond to DAD message from its some other interface.
Ofcourse a host modification is essential. Moreover, since the links are
Point-to-point, I don't see why a DAD will fail even if duplicate
addresses are configured across the interfaces of a MN. DAD in one link
may not be heard by another interface of MN. This is my thinking and
your comments are most welcome.

Finally, I would like to thank you for this draft since you have kind of
highlighted the pros and cons of both model(multi prefix and single
prefix model).

Lastly, I request you to read our draft called:multiple interfaces in
PMIP.
 
A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-jeyatharan-netlmm-multi-interf
ace-ps-00.txt

This draft is a problem statement draft. Basically looked at multihoming
issue when PMIP employs a single prefix assignement per MN. The draft
highlights, if single prefix model is used, what will be the problem
like. The problem is stated for MN which can be a MIPv6 host or an IPv6
host. The problem is further analysed in various PMIP and CMIP roaming
scenarios when the MN has Monami6 functionality incorporated. Basically,
the objective is to understand the problem in various scneraios and to
identify appropriate solutions for this issue. 

Please take a look and would really appreciate some comments and
feedback.

Thanks in advance.

BR,
Mohana
-----Original Message-----
From: Vijay Devarapalli [mailto:[email-masked]] 
Sent: Tuesday, November 13, 2007 6:08 AM
To: Netlmm
Subject: [netlmm] Multiple Interface support in PMIPv6

Hello folks,

Here is a draft that analyzes various scenarios when a mobile node with
multiple interfaces attaches to a PMIPv6 domain.

http://www.ietf.org/internet-drafts/draft-devarapalli-netlmm-multihoming
-01.txt

It talks about three cases, 1) Unique prefix per interface, 2) Unique
address per interface and 3) Shared address across interfaces. It also
addresses inter-access technology handovers.

Comments/reviews are welcome.

Vijay

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