Subject: (Reply) Query about handling Non RSVP neighbours in RSVP-TE

From: [email-masked]
Date: Mon, 4 Dec 2000 23:57:54 +0900

Hi prasanna,

	You r correct only, i.e., the first option is corect. Actually, in that paragraph,
they explained about two scenarios. First one is about non-rsvp node as downstream router.
In that case, upstream router has to send patherr. It's fine. Second one dealing with
the case, where non-rsvp node as upstream router. That means if a rsvp node, gets a path 
message with LABEL_REQUEST from a non-rsvp node,  it has to send a patherr message.
Here message is from a non-rsvp node. Am I right? 
	But only thing is, how come, a non-rsvp node sends a path message with LABEL_
REQUEST to rsvp node? I don't think, this case will arise in real time scenario.

Regards,
Reddy.

---------Original Message---------
I am eager to know the following as it was not clear to me from the draft.
 
This is one of the paragrph from the draft 07.txt

 RSVP is designed to cope gracefully with non-RSVP routers anywhere
   between senders and receivers. However, obviously, non-RSVP routers
   cannot convey labels via RSVP. This means that if a router has a
   neighbor that is known to not be RSVP capable, the router MUST NOT
   advertise the LABEL_REQUEST object when sending messages that pass
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   through the non-RSVP routers.  The router SHOULD send a PathErr back
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   to the sender, with the error code "Routing problem" and the error
   value "MPLS being negotiated, but a non-RSVP capable router stands in
   the path."  This same message SHOULD be sent, if a router receives a
   LABEL_REQUEST object in a message from a non-RSVP capable router. See
   [1] for a description of how a downstream router can determine the
   presence of non-RSVP routers.   

Does it mean that if we find a non RSVP hop in between we should stop
propogating Path mesages forward or does it mean that when we forward the
path message it should not contain Label Request Object. 

If the latter is the correct option, then how can we acheive a proper
setting up of an LSP. Because if we dont put Label Request Object in Path
message there wont be any Label Object in Resv Message and if this
haapens the we have failed to distribute labels to all the nodes along the
path.

So i think the first option is the correct one ??
Please let me know if i am wrong....

Thanx in advance

Pras

---

From: David Charlap <[email-masked]>
Date: Mon, 04 Dec 2000 11:21:19 -0500

[email-masked] wrote:
> 
>         You r correct only, i.e., the first option is corect.
> Actually, in that paragraph, they explained about two scenarios. First 
> one is about non-rsvp node as downstream router.  In that case,
> upstream router has to send patherr. It's fine. Second one dealing
> with the case, where non-rsvp node as upstream router. That means if a
> rsvp node, gets a path message with LABEL_REQUEST from a non-rsvp
> node,  it has to send a patherr message.  Here message is from a
> non-rsvp node. Am I right?
>         But only thing is, how come, a non-rsvp node sends a path
> message with LABEL_REQUEST to rsvp node? I don't think, this case will
> arise in real time scenario.

The non-RSVP node won't generate such a message - it's not running RSVP!

But it will forward such a message if it receives it.  The PHOP node
doesn't necessarily know that there's a non-RSVP router between it and
the next hop.  It may generate a Path message with LABEL_REQUEST, not
knowing that there's a non-RSVP router present on that link.  The
non-RSVP router then forwards the message.

The NHOP RSVP router that receives the message detects the non-RSVP
router (by comparing TTL values), sees that there's a LABEL_REQUEST
object (indicating that this is an RSVP-TE Path message and not a non-TE
message), and proceeds to drop the message and generate a PathErr.

-- David

---

From: Gaitonde Anandprasanna <[email-masked]>
Date: Tue, 5 Dec 2000 03:47:14 +0530 (IST)

Thanx for answering my queries to all.

I have one more query . Please see below

> The non-RSVP node won't generate such a message - it's not running RSVP!

Thats correct.

> non-RSVP router then forwards the message.

Yes, But can a PHOP node know wether the node ahead of it is RSVP capable
or not. Is there any way ?? Please let me know..

> message), and proceeds to drop the message and generate a PathErr.

Yes this clear to me now..
Thanx a lot.

Pras

> -- David

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---

From: David Charlap <[email-masked]>
Date: Mon, 04 Dec 2000 17:28:47 -0500

Gaitonde Anandprasanna wrote:
> 
> Yes, But can a PHOP node know wether the node ahead of it is RSVP
> capable or not. Is there any way ?? Please let me know..

RSVP doesn't provide a mechanism for learning this.  If a router has
this knowledge, it must be learned through some other mechanism.

Of course, if it receives some other Path on that link, and determines
that a non-RSVP router is attached, there's no reason why it can't
retain this knowledge for use with respect to Path messages sent out on
that interface.

-- David