The MPLS WG Archive

[Sachin Kalra <skalra@opnet.com>]

Takao:

Label is drawn from Label Space on receipt of RESV message. The reason
for doing this is:

At the time when LSP gets signaled, all LSRs (except Ingress LSR) decide
upon the label they will accept for the LSP, creates entry in their LFIB
and send that label to their UPSTREAM LSR. As the labels drawn have to be
forwarded upstream, so they are drawn at the time when LSR receives RESV
message (Resv message travels upstream)

This approach makes sure that each LSR gets to decide their own incoming
label for each LSP.

Take Care.
Sachin Kalra


At 01:42 PM 1/29/02 +0000, Takao Okamawari wrote:
> Hi all, 
>
> I have a question about label allocation in RSVP-TE.
> When a label is drawn from a label space?
> On receipt of PATH or on receipt of RESV? (And reason why...)
>
> RFC3209, 4.1.1.1 says, 
> "If no label is available, the node sends a PathErr
> message ..."
> Since PathErr is used to notify a failure of PATH message, 
> this reminds me that a label is drawn from a label space
> on receipt of the PATH.
>
> On the other hand, Yakov Rekhter says in his book 
> (MPLS technology and applications) that
> "When an LSR wants to send a RESV message for a new RSVP flow,
> the LSR allocates a label from its pool of free labels, 
> creates an entry in its LFIB with the incoming label set to 
> the allocated label, and sends out the RESV message..." (pp
> 153)
> (Does it mean PathErr is sent when RESV has failed?)
>
> Please let me know.
>
> Takao