Can I remove a public AS in AS-path ?

julio.gonzalez · ‎06-10-2010

HI,

the box is receiving some routes with AS-path containing a public AS. I want to send this routes to eBGP peers without this public AS. How can I remove this public AS from AS-path?

Thanks

Julio

Giuseppe Larosa · ‎06-10-2010

Hello Julio,

you cannot remove a public ASN from AS path BGP attribute.

However, as suggested in other threads you can generate locally a BGP aggregate that will be seen as originated in your AS and you can send only that aggregate to another neighbor

Hope to help

Giuseppe

francisco_1 · ‎06-10-2010

Not sure if you are allowed to aggregation a prefix generated from another AS out of your AS!!!. If yes then the received routes you can aggregated on the router as long as the route is the in the BGP table. By aggregating a prefix without the as-set, the prefix will appear as generated locally without AS attribute in the aggregated routes advertised out to other peers.

Francisco.

julio.gonzalez · ‎06-10-2010

Thanks Giuseppe,

your response solved my problem. I generate locally a BGP aggregate.

Best regards

Julio

francisco_1 · ‎06-10-2010

Julio,

What we suggested will work "BUT BE VERY CAREFUL". If the prefixes belongs to the local AS you are aggregating from, then no problem. When the summarise prefixes learned from other ASes, information hiding may result in a routing loops. By removing AS_PATH attibute and replacing with empty list will prevent BGP loop-detection mechanism from working properly.

Good luck

Francisco.