Remove BGP as number from the AS path

Unanswered Question
Nov 10th, 2009

Hello All

Is their a way to remove the first AS number (not private) from an AS


For example we are receiving a route with AS PATH 123 456 457 458 and we

want to remove the 123 AS and put in the BGP table the route with AS 456

457 458 ?

The reason we want to do this is because we have customers connected to out netowrk via an MPLS service provider who has a public AS. We receive our customer routes (who may have their own BGP) with the AS number of the MPLS provider in the path (normal BGP behaviour) but we do not want and we are not allow to announce AS number of the provider to our Upstream.

Thanks for your reply

I have this problem too.
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Giuseppe Larosa Tue, 11/10/2009 - 02:36

Hello Michael,

if IP addressing plan allows it I would create an aggregate address with option summary-only.

this will create a less specific IP prefix with a new AS path attribute originated in your ASN.

This is an approximate solution, there shouldn't be a tool to modify AS path attribute.

This is correct because on AS path is based internet routing.

Hope to help


mpalis Tue, 11/10/2009 - 02:55

This actually what we are doing at the moment. But this means that for every customer routes we have to crate a less specific prefixes and it is a problem.

The other thing is to create L2 xconnects directly to the ISP via the MPLS service provider in case we do not find any other solution.

Giuseppe Larosa Tue, 11/10/2009 - 05:06

Hello Michael,

yes with Wide Area peering over an EoMPLS pipe you can directly peer with the intended AS.

the ISP providing L2 service will disappear from AS path even if traffic is still moved in its network.

Hope to help



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