Subject: RE: resvtear msg

From: "Hariom P" <[email-masked]>
Date: Thu, 11 Oct 2001 13:33:52 -0700

>
>You're right. Egress should not send out a resvtear in response to a
>pathtear.
>
>But the ingress is required to send a pathtear in response to a resvtear to
>complete a teardown.
>
>- Vinod.

Why can't every hop that processes resvtear do the following,
1. Del matching reserv state and forward resvtear if required to the prevhop
2. And send a pathtear to the nexthop

with regards,
Hmp

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From: David Charlap <[email-masked]>
Date: Thu, 11 Oct 2001 17:24:15 -0400

> 1. Del matching reserv state and forward resvtear if required to the

It should always send a ResvTear after deleting the corresponding
state.  If the state is not present on the previous-hop router, then
that router will ignore the message.  It is unreasonable to expect a
router to know with certainty what the adjacent routers' states are.

If you send a ResvTear when the neighbor has no state, it's not a big
deal - the message will just be ignored.  If, however, you do not send a
ResvTear when you should have, the neighbor's Resv state will not go
away until it times out.  Depending on how the routers are configured,
this could be quite a long time.

> 2. And send a pathtear to the nexthop

This is wrong.  Path state should not be deleted when Resv state is
deleted.  It must remain established, and the node must continue
refreshing it.

It is perfectly legal (and not unusual in classical RSVP) for an egress
node to delete a reservation and later re-establish it with different
parameters.

Don't think of RSVP as a variation on LDP.  It is not.  A Path message
is not just a request for a label.  It establishes state in and of
itself.  It is not something that can be causally discarded simply
because some corresponding Resv state has been destroyed.

-- David

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From: Eric Gray <[email-masked]>
Date: Thu, 11 Oct 2001 19:15:04 -0400

Hariom,

    David is correct, though there is another way to look at it: sending a
PathTear message at an intermediate node would be a waste of time
since the sender will continue to send Path messages and intermediate
nodes will then be required to forward them.  A subsequent Path message
will simply re-establish the Path state deleted as a result of an earlier
PathTear message.  It doesn't really matter whether the Path message
is a result of a refresh by the intermediate node, or the result of 'passing
on' a Path message from the sender.

--
Eric Gray (mailto:[email-masked])
http://www.mindspring.com/~ewgray