AS-path prepend

[igor.hamzic]

Hi all. My organization is representing two ASN's over the same links one behind the other. As we have multiple internet links I want to make one internet link to have worse as-path to both ASNs for incoming traffic to both ASNs.

I was thinking of doing something like this:

route-map ISP-out permit 10

match ip address prefix-list ASN_1

set as-path prepend 1 1 1 1 1 1 1

!

route-map ISP-out permit 20

match ip address prefix-list ASN_2

set as-path prepend 2 2 2 2 2 2 2 2

I think that would work OK but as I have only done this when I had only one ASN on the links I would like to be sure before I implement the configuration.

Thanks for any help.

[John Blakley · Accepted solution]

Igor,

I believe what you have should work. When you apply the policy to your neighbor, you can get on a looking glass server to see if the changes have taken effect. Keep in mind that the provider can also change your prepending by policy if they want to. I've seen others on the forum that did their prepending, but when the effect that they wanted was never accomplished. If you're doing it for all traffic, does your prefix list match all networks (0.0.0.0/0 le 32)?

HTH,

John

[igor.hamzic]

Hi John,

thanks for the reply. I'll apply the configuration tomorrow and we'll see how will it go. The prefix list match the respective IP ranges of our ASN's and the route map is applied to all out going traffic coming from us.

Igor

[igor.hamzic]

John,

I think this worked all right. The configuration has been in production for two days now and all is working OK.

Thanks for the help.

Igor