BGp loadbalacing to 2 different ISPs

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Jun 25th, 2009
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ICurrently I have 1 primary link and one backup link to the Internet.

I want to enable both links to increase the bandwidth. Is it possible? Im using BGp for external and OSPF for internal.

Please let me know of any examples?


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Giuseppe Larosa Thu, 06/25/2009 - 00:30
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Hello Bao,

here are some examples:

if your company hasn't its own public ip address block NAT is involved

real outbound load balancing is possible if you have your own IP block.

if the router is only one you can use

router bgp xx

maximum-paths 2

note: this can work well if you are NOT receiving BGP full tables from your upstream providers.

inbound load balancing is more difficult to achieve you can choice how to send traffic to the internet but you have limited influence on others' choices for the return path.

Hope to help


Joseph W. Doherty Thu, 06/25/2009 - 03:34
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One issue you might encounter, since your question header mentions 2 ISPs, BGP might only use one path even with "maximum-paths 2". If this happens, you might try the secret BGP command "bgp bestpath as-path multipath-relax ".

Another option would be activation and usage of OER/PfR to provide dynamic load balancing. (NB: can be used instead of static load balancing or with it.)

luiz.alexandre.paiva Thu, 03/07/2013 - 17:12
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I agrre on wht Joseph has posted because for example one of SPs here changes a lot the AS numbers and breakes my prepends. So, when started using the "bgp bestpath as-path multipath-relax ", ballancing started really working without interference from SP.

Would like to enjoy this post to ask if someone could explain what is the impact, or if there is no problem on that.




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