Subject: Question on RSVP-TE and Resv Confirm messages

From: David Charlap <[email-masked]>
Date: Mon, 18 Sep 2000 13:38:33 -0400

When a switch running RSVP-TE receives a Resv message with a Resv
Confirm object in it, it will generate a ResvConfirm message to send
back to the egress node.

How should it send this message?

Under RFC-2205, the message would be sent directly to the recipient
without router-alert.  It would be forwarded to the egress switch like
any other data packet.

Under the RSVP-TE draft, it is unclear how this should happen.

If the message is sent in the same way, then it may not get delivered. 
The only route to the destination may not be known to the routing table.

It is also possible to send it down the explicit-route that the Path
message was send with.  But this changes the original behavior.  In
order to do this, the ResvConfirm message must have the router-alert
option set, and RSVP must participate in forwarding this message (by
looking up the corresponding path state and its ERO in order to
determine the next-hop.)

-- David

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From: Markus Jork <[email-masked]>
Date: Mon, 18 Sep 2000 16:06:34 -0400

David,

> without router-alert.  It would be forwarded to the egress switch like

This is not what RFC 2205 says. You have to use the router alert option
to implement what the RFC requires:

         A ResvConf message is sent to the unicast address of a receiver
         host; the address is obtained from the RESV_CONFIRM object.
         However, a ResvConf message is forwarded to the receiver hop-
         by-hop, to accommodate the hop-by-hop integrity check
         mechanism.

To make the hop-by-hop integrity check work and at the same time
put the address of the receiver host in the IP destination address
field, you have to use the router alert option.
And if you look at the ISI "reference implementation", you will see
that it does exactly that.

> looking up the corresponding path state and its ERO in order to

Sending it along the explicit route with the router alert is the only
way you can get things to work.

Markus

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From: "Xavier Briard" <[email-masked]>
Date: Mon, 18 Sep 2000 16:40:47 -0400

RFC2205, p. 49 (Sending RSVP messages):

Path, PathTear, and ResvConf messages must be sent with the Router Alert
IP option in their IP headers.

Xavier