The MPLS WG Archive

["wu min" <made_in__china@hotmail.com>]

Hello again,

> > Questions:
> > ----------
> > 1. Does it mean R2 has to terminate LSP for FEC with 10.2/16 address 
>prefix
> > by means of stripping the top label (the only label) and look into IP 
>header
> > to determine its finer FEC and then label the packet again with the
> > appropriate outgoing label. Is this true?
>
>My understanding of the RFC is the LSP for 10.2/16 stops at R2.  The
>the packet may or may not be label switched after R2.

The last few lines of the RFC3031 snippet from my previous message reads, 
"....In this situation, packet P can be label Switched until it reaches R2, 
but since R2 has performed route aggregation, it must execute the best match 
algorithm to find P's FEC."

It indicated that the best match algorithm must be executed to find the next 
appropriate FEC to be used for further label switching. In my opinion, 
surely this does not stop it from label switching further, right?


> > 2. Suppose the LSP is being used as a tunnel that ends after R2 and if 
>the
> > answer for my question (1) is true, then stripping the top label will 
>never
> > reveal the IP header yet since there will still be 1 or more labels. Is 
>this
> > situation valid? If so, can R2 still manage to terminate the LSP and 
>perform
> > best match algorithm? If yes, then how?
>
>I don't think you can build an LSP beyond R2 in this case, in another
>word, I don't know how you can have a tunnel that ends after R2.

What I meant is, take for example an LSR with address 10.2.153.178 is a 
remote peer and the LSP in the example is the hop-by-hop routed tunnel used 
for this peering. Obviously here the LSR is after the LSR2.



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