Subject: rfc 3031.section3.2.again

From: "Hailong Lu.sean" <[email-masked]>
Date: Fri, 18 May 2001 15:35:56 +0800

Hi,all
   Sorry about this subject again.
   From the section3.2 of rfc3031:
		"To say that one node is upstream and one is downstream with respect
	   to a given binding means only that a particular label represents a
	   particular FEC in packets travelling from the upstream node to the	
	   downstream node.  This is NOT meant to imply that packets in that FEC
	   would actually be routed from the upstream node to the downstream	
	   node"
   I can understand the first part of this section:the upstream and downstream
concepts are just meaningful when respect the binding of label and FEC.But I
can't make sure why the "routed" problem is refered particularly in the second
part of it.From my idea,in MPLS domain,after having been labeled by the ingress 
MPLS node,the packets are label switched.I mean there is no routing problem.
   thanks.

sean

---

From: Abhijit M Gadgil <[email-masked]>
Date: Fri, 18 May 2001 13:38:26 +0530 (IST)

The fact that a LSR binds a label for a FEC and sends it upstream does not
necessarily mean that the LSP gets created. This could happen in case of
DU with liberal retention mode in case of LDP.

So what the statement probably means is as follows.

"An LSR has associated a binding with a FEC and advertised upstream does
not necessarily means packet will flow along the link between Ru and Rd
_always_ . But if the packets indeed flow along the link with that Label
it shd be interpreted that the packets are for that FEC."

Hope thats correct..

-abhijit