LoadSharing Multihomed to 2 ISPs Through 2 Local Routers

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Aug 6th, 2009
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Since this doc was update back in Aug 2005 (see urls bottom page), I wonder if there is a current workaround since then.


Basically, I have the same AS in USA and London advertising diff subnets. I want to know if there is a way for BGP to know when the link gets saturated so that it can switch traffic btwn ISPs

We currently have all internet traffic via ISP-B and I want to start loadbalancing whereby if ISP-B bandwidth gets saturated, ISP-A will start receiving the load. Both ISP sends default route ( to us and:

- GLBP is sending all outbound internet to ISP-B.

- On ISP-A, we are prepending our AS which ISP-A is accepting so that ISP-B is preferred for inbound internet

- ISP-A and ISP-B is using local preference 100 and 200

ISP-B only has a 6mb pipe while ISP-A has a 10mb pipe. If bw gets saturated on 6mb pipe, I want 10mb to load-balance the bandwidth for both inbound/outbound internet traffic and to avoid asymmetrical traffic.

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paolo bevilacqua Fri, 08/07/2009 - 04:33
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It is awkward and not recommended to use traffic volume based routing. However, you can try to do that via a custom EEM script.


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