Subject: path for RSVP-TE RESV message

From: Leslie Wong <[email-masked]>
Date: Thu, 21 Feb 2002 13:16:00 -0800 (PST)

Question:

RFC 3209 states in section 4.1.1.2. Upstream:

"A node uses the label carried in the LABEL object as
the outgoing label associated with the sender.  The
router allocates a new label and binds it to the
incoming interface of this session/sender.  This is
the same interface that the router uses to forward
Resv messages to the previous hops."

I interpret it to mean that in RSVP-TE specifically
(not in the classical RSVP), the RESV message must
follow exactly the path taken by the PATH message in
reverse order (which will effectively be the route of
the data path).

Do you interpret this statement the same way?

Regards, lh.

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From: David Charlap <[email-masked]>
Date: Fri, 22 Feb 2002 10:50:59 -0500

Leslie Wong wrote:
> 
> I interpret it to mean that in RSVP-TE specifically (not in the
> classical RSVP), the RESV message must follow exactly the path taken
> by the PATH message in reverse order (which will effectively be the
> route of the data path).

This is correct.  And it will alwasy be true, unless your code is very
broken.

A node always sends a Resv message to the PHOP router.

With classical RSVP, it is possible that non-RSVP routers in between
yourself and the PHOP may cause the packet to go in a different
direction.

With RSVP-TE, however, it is a requirement that all RSVP routers be
directly connected to each other.  So the act of sending the Resv
message to the PHOP router will always send it out an interface that is
connected directly to that router.  And this is the interface that the
label will be installed on.

-- David