[Ospf-manet] LSA reduction

Richard Ogier <rich.ogier@earthlink.net> Tue, 20 February 2007 19:53 UTC

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Date: Tue, 20 Feb 2007 11:53:38 -0800
From: Richard Ogier <rich.ogier@earthlink.net>
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Subject: [Ospf-manet] LSA reduction
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Since there has been recent focus on LSA reduction, I want to give
some background and explain what the MDR draft specifies regarding
LSA reduction.

First, as stated in Section 9.2, the MDR draft allows any choice
of LSAs subject to the following two requirements:

(1) A router MUST include all Full neighbors in its router-LSA.
(2) A router MUST NOT include any non-routable neighbors in its LSA.

Any LSA choice satisfying the above requirements is therefore compliant
with the MDR draft (including the LSA methods implemented in GTNetS
whether or not they provide shortest paths).

This allows much flexibility in the choice of neighbors to
advertise in LSAs.  When several design team members were planning
to proceed with a standards-track draft based on MDRs (last year),
there was agreement that we should keep LSAs flexible,
and that specific LSA choices/algorithms would be the subject
of future work.

Although the MDR draft described some choices for LSAs (minimal LSAs,
min-cost LSAs, MDR full LSAs, and full LSAs), these were only
suggested choices, not requirements.  These specific methods
(except for the extreme cases of minimal LSAs and full LSAs)
were not going to be included in the planned standards-track
draft, and are not going to be included in the experimental draft.

The recent focus on LSA reduction, and on providing minimum-cost
routing, is therefore a topic that was considered future work
by many of us (and certainly not the main focus of the
OSPF-MANET work).  I think now is a good time to do this
"future" work.  INRIA has already made some progress in this
area, and a method for LSA reduction will soon be decided
for OSPF-MDR.  One of the questions that needs to be
answered is the following:

Q: Should the OSPF extension be *required* to always provide
minimum-cost routing, or should suboptimal routing be allowed
as an option in order to reduce overhead?

In any case, the MDR draft will describe a method for
LSA reduction that provides minimum-cost routing.
I am currently experimenting with a few candidate methods
and one of them will be included in the next revision
of the MDR draft.


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