The MPLS WG Archive

["Arashmid Akhavain" <arashmid@hotmail.com>]

Hi,


RFC 2205 in section 2.9 States that:

If the destination address does not match any local
interface and the message is not a Path or PathTear,
the message must be forwarded without further processing
by this node.

Isn't this a contradiction to what RFC3209 says?


Consider the diagram below where all nodes are
RSVP-TE capable nodes and they are all
directly connected.



        ----      PATH        ----
       |    |    ------>     |    |
       | N1 |----------------| N2 |
       |    |A              B|    |
       |____|                |____|
         |F                    C|
         |                      |
         |                      |
         |         ----         |
         |       E|    |D       |
         |________| N3 |________|
                  |    |
                  |____|




Based on 2205, N2 can build a RESV message, hands it
to IP as payload with DA = A. IP can either send it out
on interface B (most logical choice since it's N2's
local interface to the same subnet as A) or it can send it
out on interface C depending on the routing information in N2.


Are we saying that an RSVP-TE node must ignore its routing
table and it must always use the interface it received the
PATH message from to respond back with the RESV? Is
this the case for other RSVP messages as well?


If not, then if N2 sends the RESV out on interface C and N3
does not forward the packet to N1, the LSP is not going to
be established.

But if N3 forwards the packet to N1 without any further
processing, although N1 receives the RESV message through its
interface F, it can still identify the corresponding PSB (Note
that PSB is associated with link AB) and associate the arrived
label with link AB.


Regards,
Arashmid Akhavain



David Charlap wrote:

>Leslie Wong wrote:
>
>I interpret it to mean that in RSVP-TE
>specifically (not in the classical RSVP), the
>RESV message must follow exactly the path taken
>by the PATH message in reverse order (which will
>effectively be the route of the data path).

This is correct.  And it will alwasy be true, unless your code is
very broken.

A node always sends a Resv message to the PHOP router.

With classical RSVP, it is possible that non-RSVP routers in
between yourself and the PHOP may cause the packet to go in a different 
direction.

With RSVP-TE, however, it is a requirement that
all RSVP routers be directly connected to each
other.  So the act of sending the Resv message
to the PHOP router will always send it out an
interface that is connected directly to that
router.  And this is the interface that the label
will be installed on.

-- David



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