Subject: [MOBILE-IP] Consensus for the extensions template defined in MIER

From: Basavaraj Patil <[email-masked]>
Date: Tue, 11 Jan 2000 20:58:48 -0600

The MIER draft (draft-ietf-mobileip-mier-00.txt) states that all new
extensions defined for Mobile IP in the future MUST follow the
template that is specified in the document.
The difference from the existing definition specified in RFC2002 is
that adds a subtype field and the length field is increased two
octets.

If you have concerns or disagree with this proposal, please express it
on the mailing list by the end of this week.

-Basavaraj Patil

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From: Jouni Malinen <[email-masked]>
Date: Wed, 12 Jan 2000 08:44:58 +0200

> on the mailing list by the end of this week.

Doesn't this break the compatibility with RFC 2002 compliant
implementations completely as far as new skippable extensions are
concerned? The two octet length field could be used in non-skippable
extensions as they should cause the whole message to be silently
discarded (if the receiver does not recognize them), but I didn't see
that kind of requirement in the draft.

This would mean that all the new extensions (even skippable) would be
required to use the proposed extension format. An old implementation
not knowing of the MIER draft would be unable to parse the extensions
as the length field would be in a different place and of different
size. So messages with a new _skippable_ extension would be dropped.

Is this kind of compatibility breaking approach all right? Are we
trying to make a need for some complicated method of finding out
whether each MN, FA, and HA on the path support MIER before an agent
could send any new skippable extensions? Or should the agent try once
and after some time try again without the MIER type extension? I'm not
welcoming this kind of complexity. It would be easier to change the
extension format in RFC 2002bis and forget about the compatibility,
but I don't think it is acceptable to break the compatibility this way
with RFC 2002.

I do, however, think, that subtyping of extensions would be a good
thing. Subtyping can be done with one byte length field in the
original place for the skippable extensions so that the compatibility
is maintained. In addition, I don't see any good enough reason for
requiring that every new extension must use subtyping.

--
Jouni Malinen

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From: Wolfgang Schoenfeld <[email-masked]>
Date: Wed, 12 Jan 2000 11:16:26 +0100

> Basavaraj Patil wrote:

I disagree with the proposal, for the following reasons.

Let me view types and subtypes as a means of multiplexing a control channel.
Adding a subtype field to the type field of Mobile IP has two effects.
First, there are more bits,
hence more channels can be multiplexed.
Second, these bits are partitioned in two groups,
hence implementations may use a two-layer nesting of switches (if-statements).
Neither from the discussion in this mailing list
nor from the extensive tests we carried out with current Mobile IP
can I conclude that Mobile IP needs more channels
or a two-layer arrangement of these channels.

Though this should suffice as a justification (I think that
the necessity of adding something should be proved,
not the necessity of not adding it),
I'd like to repeat some known arguments with which I agree.
First, existing software would have to be re-implemented.
Second, existing proposals for protocol extensions would have to be re-worked.
Third, there is some chance that future proposals are hard to fit
into the MIER format, anyhow.
Fourth, having more bits for the type field might entail
the temptation to overburden Mobile IP.

-- Wolfgang Schoenfeld
GMD-IPSI, Dolivostr. 15, Room 128, D-64293 Darmstadt
+49-6151-869-865 (Phone), -818 (FAX)
+49-170-2285450 (Mobile Phone)

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From: Pete McCann <[email-masked]>
Date: Wed, 12 Jan 2000 09:33:57 -0600

Basavaraj Patil <[email-masked]> (BP) writes:

BP> If you have concerns or disagree with this proposal, please express it
BP> on the mailing list by the end of this week.

I do not think we should require all new extensions to follow the MIER
format.  MIER might not be appropriate for all situations and could
unnecessarily slow down current standards efforts.  New extension
proposals should follow the MIER format if and when appropriate.

-Pete