Subject: non-RSVP routers.

From: Subhakar K S <[email-masked]>
Date: Fri, 1 Feb 2002 23:22:40 -0800 (PST)

How does an intermediate router finds if its
downstream router is RSVP aware or not.

thanks,
S.

__________________________________________________
Do You Yahoo!?
Great stuff seeking new owners in Yahoo! Auctions! 
http://auctions.yahoo.com

---

From: Ajay Simha <[email-masked]>
Date: Sun, 3 Feb 2002 09:40:37 -0500 (Eastern Standard Time)

On Fri, 1 Feb 2002, Subhakar K S wrote:

SKS>
SKS>How does an intermediate router finds if its
SKS>downstream router is RSVP aware or not.

In the context of MPLS-TE if we configure TE we should enable RSVP at the
seme time.  If we go with this assumption, then if we receive IGP LSA/LSPs
describing a link then we can assume it has RSVP turned on.

Of course if this is not the case we'll know when we don't receive RESV
messages after we send PATH messages :-)

-ajay

SKS>
SKS>
SKS>thanks,
SKS>S.
SKS>
SKS>__________________________________________________
SKS>Do You Yahoo!?
SKS>Great stuff seeking new owners in Yahoo! Auctions!
SKS>http://auctions.yahoo.com
SKS>

-- 
Ajay Simha
MPLS Deployment Engineer
IOS Technology Division
Cisco Systems
(919) 392-3141

"Study as if you were to live forever
 Live as if you were to die tomorrow"

 - Mahatma Gandhi

---

From: [email-masked]
Date: Sat, 2 Feb 2002 13:22:46 -0500 (EST)

Hello,

Please see the last paragraph in RFC 2205, section 3.8:

"With normal IP forwarding, RSVP can detect a non-RSVP hop by comparing
the IP TTL with which a Path message is sent to the TTL with which it is
received; for this purpose, the transmission TTL is placed in the common
header.  However, the TTL is not always a reliable indicator of non-RSVP
hops, and other means must sometimes be used.  For example, if the routing
protocol uses IP encapsulating tunnels, then the routing protocol must
inform RSVP when non-RSVP hops are included.  If no automatic mechanism
will work, manual configuration will be required."

However, RSVP-TE will not work with non-RSVP routers.  Please see section
4.2.5 of RFC 3209.

Thanks,
-Ben

---

From: David Charlap <[email-masked]>
Date: Mon, 04 Feb 2002 11:48:27 -0500

> downstream router is RSVP aware or not.

RSVP does not provide a mechanism to detect a non-RSVP router
downstream.  Any such detection must be through means beyond the scope
of RSVP.

However, RSVP can detect one upstream.  RSVP's common header includes a
TTL field, which is assigned to match the IP header's TTL.  If an RSVP
message gets forwarded through a non-RSVP router, the IP TTL will be
decremented, and won't match the RSVP TTL.

In classical RSVP, the "adspec break" bit is set in the ADSPEC object to
inform nodes further downstream that there are non-RSVP routers along
the path.

In RSVP-TE, non-RSVP routers are not supported, so a PathErr would be
generated once the non-RSVP router was detected.

See RFC 2205 and RFC 3209.

-- David