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BGP As override

sourabh1000_2
Level 1
Level 1

hello friends,

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

1 Accepted Solution

Accepted Solutions

Giuseppe Larosa
Hall of Fame
Hall of Fame

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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3 Replies 3

Giuseppe Larosa
Hall of Fame
Hall of Fame

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

thank you...Giuseppe, for providing nice expln.

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