The MPLS WG Archive

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

Hi,

This question has been asked a number of times. If you read the LSR-MIB carefully it seems that a swap is modeled as a pop followed by a push. Therefore if you want to terminate an LSP and you know for sure that all the traffics inside that LSP are MPLS traffic, then setting N-POPs =2 and mplsOutSegmentPushTopLabel= true(1), will pop the top label and swap the lower ones.

However, it seems that there is no use for N-POPs >2, because as you said, an LSR needs to look at the lower labels to decide whether to terminate them or not.

Yours,
-Shahram 

> -----Original Message-----
> From: Paul Mannion [mailto:Paul.Mannion@s3group.com]
> Sent: Wednesday, June 27, 2001 9:26 AM
> To: mpls@UU.NET; mpls-ops@mplsrc.com
> Subject: Q RE N-POPS Value in LSR MIB
> 
> 
> Hi,
>     Sorry if this has been answered already.
> 
>     I'm a little confused as to how the N-POP value in the LSR
>     MIB is used in practice.
> 
>     i.e. if the N-POPS is > 1, say 2, which of the following is the
>     correct behaviour assuming an incoming label stack size of 3.
> 
>     1] Pop 2 labels and lookup and forward according to the remaining
>          label.
> 
>     2] Perform a lookup using each label before it is 
> "popped", if this
>         is the case i'm not sure what use the N-POP value is as the
> action
>         is specified by the lookup result in each case.
> 
>         thanks in advance
> Paul
> 
> 
>