Subject: Possible optimization to Hitless Restart draft

From: Mark Mitchell <[email-masked]>
Date: Wed, 8 May 2002 11:35:20 +0100

Hi there,

I have a proposal for a possible optimization to the OSPF Hitless Restart
draft. I would welcome comments on whether the proposal is valid, worthwhile
or otherwise.

In section 2.1, the draft states that 'after the grace-LSAs have been sent,
the router should store the fact that it is performing hitless restart along
with the length of the requested grace period in non-volatile storage.'.

We were wondering whether it is necessary to store the length of the grace
period before restarting. Instead, our idea is that the restarting router
discovers the grace period it requested from the grace LSAs it originated
prior to the hitless restart and which it will receive during hitless
restart (from its neighbors). At the same time it will be receiving the
other LSAs that it originated prior to the restart and accepting them as
current (until Hitless Restart is over).

- Since the grace period should start at the time the grace LSA was
originated, the remaining duration of the grace period can be calculated as
the grace period requested in the LSA minus the age of the LSA itself.

- Note that if the restarting router does not receive any grace LSAs, its
neighbors cannot be helping it to undergo hitless restart and so hitless
restart will soon end.

- If the restarting router does not receive any grace LSAs or pre-start
router or network LSAs from its neighbors, it might never exit hitless
restart. This could be avoided by the restarting router assuming the default
grace period until it receives its pre-start grace LSA containing the actual
grace period.

Obviously the proposal in the draft (of storing the grace period in
non-volatile storage) is entirely valid, but this seemed like a possible
enhancement to avoid needing to do this. As mentioned before, we would
appreciate any comments.

Thanks,

Mark

-------
Mark Mitchell
DC-OSPF Development Manager
Data Connection Ltd
Tel: +44 20 8366 1177
Fax: +44 20 8363 1039
Email: [email-masked]
Web: http://www.dataconnection.com

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From: Acee Lindem <[email-masked]>
Date: Wed, 8 May 2002 10:14:45 -0400

Mark,

It seems like it would work ok but I don't see it as an optimization.
Rather, it is an implementation tactic that may or may not be easier
depending on the environment.

Also, if you (or your marketing group ;-) wants to handle both planned
and unplanned restarts you need to be able to determine this fact and
are going to need to keep track of you restart reason (at a minimum) in
non-volatile storage (with no restart reason defaulting to an
unplanned restart). Note that in the case of the unplanned restart, the
grace LSAs are sent when you come back up rather than when you are
about to go down.

Thanks,
Acee

--
Acee