The MPLS WG Archive

[David Charlap <david.charlap@marconi.com>]

venkir@samsung.co.kr 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