mpls ATM control-vc command

Unanswered Question
Mar 29th, 2010
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I am having difficulty understanding the following commands:

int ATM 3/0.2

mpls ip

mpls atm 2-3

mpls atm control-vc 5 31

Should I not have mpls atm control-vc X 31 where X either value 2 or 3?

I thought the 5 was the VPI which must fall within the range specified in the mpls atm 2-3?

In other words - how can the value 5 differ from 2-3?

Thank you for explaining


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Giuseppe Larosa Mon, 03/29/2010 - 06:19
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Hello Walter,

this should be legitimate configuration

in ATM mode MPLS LSP are created on demand as SVCs so the control channel can use a different VPI value

the command

mpls atm 2-3

says that SVCs created on demand will have VPI 2 or 3 and this provides a moderate label space (not very big in comparison to packet based MPLS)

I would say this is even more clear and clean as a configuration

I may be wrong but reserved VCI values 0-31 exist when VPI = 0 not for non zero VPI values.

all the LDP messages will travel on 5/31 with no risk of interference with SVCs

Hope to help



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