The MPLS-OPS Archive

["M. ELK" <elkou141061@hotmail.com>]

Hi

Quote
>Do I still miss something or is the FAQ-example just not built
>properly (when saying that R1 pushes the new label, but the LSP starts
>at R2)?

Unquote

AFAIK , believe the FAQ-example was not worded properly .

Brgds

>From: Andreas S <dg6gai@gmail.com>
>Reply-To: Andreas S <dg6gai@gmail.com>
>To: mpls-ops@mplsrc.com
>Subject: [MPLS-OPS]: Re: : Newbie Questions
>Date: Wed, 18 May 2005 11:28:27 +0800
>
>Hi,
>
>thanks everyone so far for the replies.
>
>I think my first question on the start and endpoint of the nested LSP
>caused a little bit of confusion, as I haven't quoted every detail of
>the example from the FAQ on this website.
><http://www.mplsrc.com/faq2.shtml#MPLS Components>
>
>Again the picture:
>
>|------| 1                                    1 |-----|
>| R1   |--\                                 /---| R5  |
>|------|   \   2          2          2     /    |-----|
>             \|------|   |-----|   |-----| /
>              | R2   |---| R3  |---| R4  |/
>              |------|   |-----|   |-----|
>
>Most of the replies assumed that the level 2 label is pushed at R2,
>and then I agree that the nested LSP starts at R2.
>However, the example states that *R1* pushes the new label for R2 (and
>also swaps the label for R5), and that the nested LSP is R2-R3-R4.
>
>If this is correct, I don't understand how this matches the RFC3031,
>which says that a LSP begins with the LSR that pushes the new label
>onto the label stack, which was basically the core of my question when
>I wrote "...the R2-R3-R4 path should start at R1 and finish at R5...".
>
>I think M. Elk's reply said what I meant (here LSP2 start at R1):
>"we have one LSP ,say LSP1  as R0,R1 and R5 .
>  we have another LSP , say LSP2 as R1,R2,R3,R4,R5 .
>  when R1 receive label packet over LSP1  , it swap the label and push
>the labeled packe inside LSP2 to reach R5 . so R1 will transmit the
>packet with 2 label , the top is for LSP2 and the bottom is for LSP1."
>
>Do I still miss something or is the FAQ-example just not built
>properly (when saying that R1 pushes the new label, but the LSP starts
>at R2)?
>
>
>Sorry for the confusion and thanks again for the replies to the other 
>points!
>
>Cheers,
>  Andreas
>
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