BGP As override

Answered Question
Oct 17th, 2009

hello friends,

pls explain as-override feature in brief if possible please give me the example

I have this problem too.
0 votes
Correct Answer by Giuseppe Larosa about 4 years 6 months ago

Hello Sourabh,

neigh x.x.x.x as-override allows to a PE router to change the private ASN used by a CE node on an eBGP session running on a VRF access link.

the private ASN is changed in the PE ASN.

another CE node on another VRF (=connected to another PE node) will see the eBGP route coming from first site with an AS path of:

provider-ASN provider-ASN

instead of:

provider-ASN site1-ASN

this allows to use the same private ASN on all sites of a customer.

That is a clear management advantage for a service provider.

This because BGP by default doesn't accept BGP routes with an AS path attribute that contains local AS number.

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Sat, 10/17/2009 - 10:20

Hello Sourabh,

neigh x.x.x.x as-override allows to a PE router to change the private ASN used by a CE node on an eBGP session running on a VRF access link.

the private ASN is changed in the PE ASN.

another CE node on another VRF (=connected to another PE node) will see the eBGP route coming from first site with an AS path of:

provider-ASN provider-ASN

instead of:

provider-ASN site1-ASN

this allows to use the same private ASN on all sites of a customer.

That is a clear management advantage for a service provider.

This because BGP by default doesn't accept BGP routes with an AS path attribute that contains local AS number.

Hope to help

Giuseppe

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Posted October 17, 2009 at 9:45 AM
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