topic Re: BGP RIB Out AS Path in General Topics

BGP RIB Out AS Path

GFN182 — Wed, 15 Dec 2021 14:49:00 GMT

I am using BGP between two ISP's. On one of them my AS number is listed one time by each prefix. On the other ISP my AS number is listed 6 times by each prefix. The ISP with 6 AS numbers is a lower preference.

Anyone know why?

Re: BGP RIB Out AS Path

aleksandar.astardzhiev — Wed, 15 Dec 2021 16:32:08 GMT

Hi @GFN182 ,

If I understand you correctly, I believe you are talking about "AS path prepending". This is commond technique used to design which path will be primary and which backup. If you recall from BGP path selection, route with shortest AS path will be prefer. In addition AS path is one of the first critieria which device will use to compare paths to same destination.

AS path prepend will copy the last AS from the path and append it n-times.

Re: BGP RIB Out AS Path

GFN182 — Wed, 15 Dec 2021 16:39:43 GMT

It was a setting under one of our Export rules.