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Load balancing running BGP

I have a 7513 router with two seperate T1 connections to two seperate providers. Running BGP with full routes to both. During peak periods one connection runs at 100% capacity constantly while the other runs at 20% max capacity. My upstream providers tell me nothing other than static routing takes a priority over BGP. However, no matter what I route statically it makes no difference at all. Static routes just have not effect. Can anyone point me in the right direction to balance my load out??

Community Member

Re: Load balancing running BGP


maybe it can be helpful if you check the AS pathes of both connections with an "independent" looking glass. If one path is longer the other one will be preferred.

An other possibility, check the incoming BGP routes of each of your provider.

We just experienced different local preferences but did not change our configuration which could cause this.

Another tip to avoid uneeded traffic. Set up separate ip as-path access-lists to on the BGP sessions to your upstreams which deny forwarding the BGP routes received from each other provider.

Actually if you don't influence both BGP session by using prepends, metric or something like that,

a kind of "natural" load balancing should use both connections in equal shares.

If all tings, mentioned above, don't match, observe the traffic behaviour of your connected customers. We also had to recognise that some customer only use special paths which cause a

unlikly utilization.

Community Member

Re: Load balancing running BGP

In what direction are you hitting 100%. If this is inbound you need to look at what you can do to make the lower utilised path more attractive. If you have just one prefix to announce you're pretty stuck but its not necessarily impossible. In this case you could look to see if your upstream providers support communities to prepend your announcements upstream this may have some effect, making the heavily loaded circuit less preferred when its announced to other providers - who them may select the other ISP's route to you. If you have more than one prefix you could prepend your AS on the heavily loaded link to make it less attactive thus moving reply traffic (inbound) to the other ISP. Its possible you could split your announcement into two and then make half preferred via one ISP and half preferred by the other.

If the load is high outbound you need to adjust the local preference for some of the routes learned from the less loaded ISP. This will make these routes better and move the outbound traffic to that path.

All load balancing in BGP is tricky, from the above I'd assume its the inbound traffic thats the problem.

You need to make small changes and observe the effect, otherwise you'll just move all the traffic and gain nothing.

Community Member

Re: Load balancing running BGP

Check to see that you have ip route-cache turned off. You may have to have your ISP's also turned it off for your interface from their end.

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