BGP question

[jefo]

I have have a setup where BGP with AS "X" has received a route from AS "Y". I have to ways between AS "Y" and "X" . How do I get AS "X" to advertise this route back to AS "Y" when it has originated from "y"?

I hope you can help, thanks.

[Harold Ritter · Accepted solution]

The BGP loop detection takes place when the eBGP updates are received. So in your scenario, AS X will advertise the prefixes to Y even if the AS-PATH contains Y. AS Y would then see its own ASN in the AS-PATH and reject the prefix. Assuming that AS Y is discontiguous, you can use the following command to accept the prefixes even if the local AS number is part of the AS-PATH received from AS X:

neighbor x.x.x.x allowas-in

This would have the effect of using AS X as a transit AS between the disconguous parts of AS Y.

Care should be taken when using this command as it bypasses the regular BGP loop detection.

Hope this helps,

[jefo]

Hi hritter

It was exactly this command that I needed. Everything works the way I want to now.

Thank you very much for your time and help.

Best regards,

Jesper