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Fault tolerance and / or Load Sharing with BGP

Hello, we have a 3640 with 128MB RAM with two serial interfaces connecting us to two different ISPs. Our AS is set up, the ISPs are sending us full routes, but I do not totally understand what exactly we are getting out of BGP. The way I understand it, a multihomed ISP configuration with BGP is not possible to load balance but instead you can load share it by sending say half of the routes out one interface and the other half out of the other interface.

We have been monitoring our interfaces, and one ISP is basically sitting idle while the other is taking all of the traffic. Even when one ISP is completely saturated, the other link sits idle. What is the recommended way to handle this situation? Fault tolerance is also a concern of ours. What if one link is unavailable? What is required for the other link to 'fail over' resulting in no down time noticeable by customers?

Thank you.


Re: Fault tolerance and / or Load Sharing with BGP

There are many way to get load sharing accomplished with BPG, although it is a bit more involved with multiple ISPs. Just make sure you look at your traffic leaving and coming back into your AS as different issues and handle them separately. The following link shows good BPG information and configuration examples that should help you.

Also the support Page:

Using Route-maps with either set ip next-hop can be used for outbound loading, as you mentioned forcing some traffic out one exit point. Assuming you have mulitple ip networks you could use MEDs/AS Path prepend/etc to effect inbound traffic. BGP is a very deep and has many widgets. If you lesson the scope of your question once your underway poeple on this list will be able to assist you very well.

Hope this helps,


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