Hi Dave, and other folks knowledgeable about IPv6 addressing model,
[EMAIL PROTECTED] CCed, please reply only to [EMAIL PROTECTED]
While working on the issues of which addressing model to use in
NetLMM, I think I got confused with issues involved the IPv6
addressing model (or its assumptions.)
I would therefore like to ask you if a potential NetLMM addressing
model (per-MN subnet prefix [RFC3314]) would, in some situations,
conflict with the IP addressing model.
Background
----------
Dave's draft on issues involved with multilink subnets
[draft-thaler-intarea-multilink-subnet-issues] list some assumptions
of the IP addressing model, but there might be other that are not
specific to multilink subnets. I'd therefore like to ask you about
possible conflicts between IPv6 and RFC3314 addressing model.
We are considering the situation of mobile nodes (MNs) attached to a
NetLMM domain. The NetLMM domain span multiple access links, each
served by a given access router (AR). A MN attaches to one link, and
hence to one AR.
( NetLMM domain )
/ | | | \
AR AR AR AR AR
/ \ \ / \ \
MN MN MN MN MN MN
If all of the MNs in the domain uses a common subnet prefix we
obviously end-up with a multilink subnet, which is problematic as
described in Dave's draft. Now a simple way to avoid multilink subnet
issues is to use a per-MN subnet prefix, as in the IETF
recommendation to 3GPP [RFC3314]. That way, each of the MN moves has
a different prefix and hence none of the prefix spans more than one
link, thus avoiding multilink subnet issues.
Issue
-----
Such model has however raised a question, which is orthogonal to
multi-link subnets issues. RFC3314 was proposed for use in a scenario
where the link between the MN and its AR is point-to-point. Now if we
consider a broadcast/multicast capable link-layer technology such as
Ethernet, then we would have a situation in which, on a given link,
the broadcast domain and hence the link-local scope are larger than
the any of the per-MN subnet prefixes scope (as illustrated below
when 3 MNs A, B and C are connected to one such link served by one AR
R).
A subnet prefix scope: -R-------A------------------
B subnet prefix scope: -R---------------B----------
C subnet prefix scope: -R------------------------C-
link-local scope: -R-------A-------B--------C-
L2 broadcast scope: -R-------A-------B--------C-
Do you think that this situation (i.e. link-local scope larger than
subnet prefix scope) would conflict with the IPv6 addressing model,
or any of its assumptions?
Many thanks in advance. Best regards,
--julien
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