eBGP Manipulation

[kramer977]

Hey everyone,

Have a BGP related question. Lets say, Site A (me) has two EBGP links with Site B, two different ISP providers (ISP 1 and 2). The same prefixes are advertised out of both links from the client (Site B). Traffic will be initiated from my side, Site A to Site B. I'm looking to manipulate the traffic outbound to prefer ISP 1 over 2 (primary and secondary).

1. Plan is to set a higher local preference on the primary ISP link. Create a route map/prefix list and apply the RM on the BGP neighbour, "IN" direction so it's received by our site.
2. Here is my question. Is it advisable to also create a route map/prefix list and applied it to the "OUT" direction on the same BGP neighbour to ensure the return traffic also follows via the primary ISP 1 link, for eg, I can prepend the neighbourship link on ISP 2 to make it longer so ISP 1 appears shorter and more desirable. Is this advisable or not at all required?

Any other feedback is more than welcome, besides my question

Thanks!

[Francesco Molino]

Hi

You're right. You need to have a rmap in to prefer prefixes from 1 isp over the other.
Then for return traffic to control it, you will need to advertise out your prefixes with a rmap out which will prepend the as over isp2 to make it worst compare to the one received from isp1.

[Evgeniy Prichinin]

It will work for traffic between A and B, but not for ISP2 traffic directed to A. Using Backup community from ISP2 is only way to achive using ISP2 as backup.