BGP AS Path Prepending

RouterOS Forwarding Protocols
1

Hello All,

I know the answer to this question (and I am sorry for asking), however another MT user does not believe me and I need to prove a point.

Here is the example:

I have two carriers, ISP 1 and ISP 2 to which I am announcing the same prefix, 192.0.2.0/24. I want to preference ISP 1, so that any traffic destined for my prefix is routed in and out via ISP 1, and then route via ISP 2 when ISP 1 fails. I would prepend my AS Path (something like) 3x to ISP 2, correct? Feel free to give a short and long answer, if you like. The more detail, the better. Brownie points if you have a MT Certification :wink:

Thanks,
Christopher H.

2

Basically yes, prepend is going to do the job, of course you have to check other methods just to be on the safe side. There is a lot of detailed information on https://wiki.mikrotik.com/wiki/Manual:Simple_BGP_Multihoming#Main.2FBackup_link_setup if you want.