Subject: RE: Adopting draft-francois-ordered-fib-00.txt as a WG document

From: "Don Fedyk" <[email-masked]>
Date: Mon, 21 Nov 2005 23:18:08 -0500

Oliver

A couple of questions for the group. So far the work accepted by the
group mainly been focused around routers immediately adjacent to a
failure or neighbors of routers adjacent to a failure.  This work
extends the ordering to all routers in an area. 

The law of diminishing returns is that most of the benefit is for the
neighboring routers and the extra effort is for a small amount of
traffic.  So I think we need to make sure that operators feel this type
of extension is important. I believe you need to know that all routers
within the area have the capability to ensure orderly operation.

Other questions: 
If one router in the area does not support the feature what is the
action? 
Also if an unplanned event occurs during ordering would you immediately
shut of the fib ordering? 
This draft would replace the micro loop analysis and Path locking via
safe neighbors draft? While it is not perfect it also reduces the effect
of changes (planned or unplanned) when used in conjunction with loop
free alternates. 

Regards,
Don 

> Would you agree if section 2 of the draft was updated and 
> link down events were removed and only the following events 
> were supported :
> - metric change
> - link up
> - router down and router up (overload bit transition in ISIS)
> 
> This would mean that if a router wants to either supports 
> graceful manual link shutdown or graceful shutdown of fully 
> protected link, it should first advertise the considered link 
> with a very large metric and later remove it from its link 
> state packet.

> Olivier

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From: Stewart Bryant <[email-masked]>
Date: Tue, 22 Nov 2005 08:20:00 +0000

Don

That is incorrect.

With PLSN ALL routers that have a path affected by the change may
have their convergence delayed as a result of the change. This
may extend to many hops from the failure.

Even thought you are protecting only a single link with basic
repair, PLSN needs to be deployed throughtout the network.

>If one router in the area does not support the feature what is the
With PLSN and oFIB all routers in the area MUST support the
mechanism. In both cases the consequence of a router using traditional
convergence may be a sustained loop. With both mechanisms it is
possible to detect the presence of a non conforming router and
inhibit the loop protection mechanism.

The tunneling mechanism that we proposed is much more tolerant to
non-conforming routers.

>shut of the fib ordering? 
Yes

> of changes (planned or unplanned) when used in conjunction with loop

It is by no means as simple as that.

- Stewart