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Setting up Internet links with two different ISPs in redundant and load sharing configs

We want to setup Internet links with two different ISPs in redundant and load sharing configuration. Traffic flowing through links is FTP, HTTP, SMTP etc. Kindly explain how this can be achieved we have two different IP ranges assigned by our ISPs then how do we configure our Internet setup so the result can be achieved. Let us know what all our ISPs need to do for setting up this BGP configuration and what configuration we have to do at our end. Please note we want achieve this ISP multi-homing using single CISCO 2610 router.

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You need to get an ASN, and then setup BGP routing with both ISPs. You will advertise both address ranges to both ISPs. Incoming traffic will take the shortest AS path. How you handle outbound routing depends on how much memory you are willing to put in your router. With minimal memory you can simply use multiple static default routes; this will produce fairly even balancing, but not always optimal routing (you may go through ISP A to get to a customer of ISP B).

You can have one ISP send you their customer routes, and use the other ISP as a default (and fail over to the first ISP if that connection goes down); this will probably require 32-64MB RAM. Or you could have both ISPs send you full routes, which will require 256MB RAM (I don't know offhand if a 2610 can hold this much). See the section on BGP in Vincent Jones's book "High Availability Networking with Cisco".

This was first published in September 2002

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