Solved: How to determine the amount of prepends to add to my route-map

Karl Greenwood · ‎08-31-2016

I currently have two different ISP's and I use BGP for redundancy. I am seeing about 50% more traffic coming inbound on one ISP over the other. So what I would like to do is prepend my AS using a route-map to one of the ISP's in order to create a more equal balance of inbound traffic. I understand that this is not an exact method of load balancing inbound and to my knowledge there isn't an exact science to inbound load balancing when using BGP with two different ISP's but I would like to try to make the inbound traffic more equitable across both ISP's.

So my question is. Is there a way to determine how many prepends I should add to the route-map before I implement this change or do I simply add a prepend and note the traffic pattern change and then add prepends accordingly?

Thank you in advance for any assistance.

K.

Richard Burts · ‎09-01-2016

I do not believe that there is a good way to determine how many prepends to use before you make the change. You should add one, check on traffic distribution to see the effect, and then add another until you get the approximate balance that you want.

HTH

Rick

HTH

Rick

View solution in original post

skpooe001 · ‎08-31-2016

Hi K,

Look at the AS numbers on your BGP table and if equal you can add one/two AS extra to your prepend route-map. Less desired route must have more AS numbers than desired route.

you can also Classify your traffic from high to low priority between the ISPs

1. 50 % of the traffic to ISP 1 and prepend or use Med to the other 50 % you allowing on ISP 2.

2. 50 % of the traffic to ISP 2 and prepend or use Med to the other 50 % you allowing on ISP 1.

also use IP LSA for the two links to your ISP.

You the link below for more info (maximum-paths)

https://learningnetwork.cisco.com/thread/42531

Hope it helps Mate :)

Richard Burts · ‎09-01-2016

I do not believe that there is a good way to determine how many prepends to use before you make the change. You should add one, check on traffic distribution to see the effect, and then add another until you get the approximate balance that you want.

HTH

Rick

HTH

Rick