The MPLS WG Archive

["LIAN Franklin FTLD/IAP" <franklin.lian@francetelecom.com>]

wu min wrote:
> 
> 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?
> 

Yes, it is true that it does not stop it from being "switched" from R2,
but you will have TWO (2) LSPs involved in this case.  The LSP_1 stops
at R2, and LSP_2 starts at R2.  When the packet is processed at R2,
it is NOT a simple label swapping, there is route lookup or label
pushing involved if necessary.

Wish this can help
Zidan

> > > 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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