Subject: routing

From: "Srikanth Uppuluri" <[email-masked]>
Date: Tue, 30 Jan 2001 11:05:18 +0530

Hello,
   I have the following basic doubts:

1) It is mentioned that RSVP PATH messages follow normal routing paths. In 
such case how it possible that all the PATH messages ( including the refresh 
messages ) travel along the same nodes in the network?

2) How is it ensured that data packets follow the same path where the 
resources are reserved for that session?

Thanks
Srikanth
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

---

From: Lixia Zhang <[email-masked]>
Date: Mon, 29 Jan 2001 22:22:20 -0800

At 11:05 AM 1/30/01 +0530, Srikanth Uppuluri wrote:
>such case how it possible that all the PATH messages ( including the 
>refresh messages ) travel along the same nodes in the network?

RSVP msgs follow the path pointed by the router's forwarding table.
Unless the net does multi-path routing, otherwise all PATH msgs can only 
travel along the same nodes as pointed by the forwarding table (till the 
route changes, then future msgs will follow the nodes along the new path)

>resources are reserved for that session?

both PATH msgs and data packets follow the router's forwarding table.

---

From: David Charlap <[email-masked]>
Date: Tue, 30 Jan 2001 10:26:35 -0500

Srikanth Uppuluri wrote:
> 
> 1) It is mentioned that RSVP PATH messages follow normal routing
> paths.

More precisely, the Path messages are sent to whatever next-hop address
the router will use for forwarding the session's data packets.  If some
unusual routing is used for a given destination, that routing should
also be used for the Path messages.

> In such case how it possible that all the PATH messages (including the

If/when the routing tables change such that the data starts flowing out
a different interface, then the Path refreshes will start going out the
new interface as well (and the former next-hop will expire the Path when
it sees that the refreshes have stopped.)

The new next-hop will see the Path message as new instead of a refresh,
since it hasn't processed the session before, and will establish state. 
When the new path converges with the old path, the router at the merge
point (which could be the destination) will send out a Resv message.

Then the reroute will be complete.

> resources are reserved for that session?

The data packets always follow the router's forwarding table.  So do the
Path messages.  If the table changes, then both data packets and Path
messages start going out the new interface.

-- David