Cisco Blog: Load Balancing Between Two ISPs with NAT

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November 16, 2007

Load Balancing Between Two ISPs with NAT

In the consulting world, I get this request all the time: "I've got two ISPs with equal bandwidth connections for redundancy. Can I load balance between them?" Well, Cisco just published an article addressing exactly this. Check out the link below - it provides a configuration that uses features such as SLA to ping remote devices and make sure they are online before using a specific interface. There were some interface tracking features in here that I didn't even know existed! Nice!!!

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_configuration_example09186a00808d2b72.shtml

UPDATE: NIL just published a guide on Load Balancing using BGP, also pretty sweet.

Posted by JC at November 16, 2007 9:32 AM

Comments

So could we do this without nat?

It would be nice to use all my bandwidth at a site with out having to nat at the router.

Posted by: Mike at November 16, 2007 11:53 AM

Without NAT? Sure, use a routing protocol :)

http://www.cisco.com/warp/public/105/46.html

Posted by: Rob at November 19, 2007 2:08 PM

I've been reading that using two different NATd source addresses you may experience some websites that do not work? Has anyone experienced this?

I've search for a while any only found two articles.

Here's an article using Junipers ECMP:
http://bart.motd.be/experimenting-ecmp-netscreen

Posted by: Anonymous at March 12, 2008 11:47 AM

Is it possible to load balance between two ISP's with out nat ( two default routes) ?

Posted by: ragu at April 2, 2008 12:48 AM

Hi! Could anyone give me some design or network diagram in load balancing with two different ISP's? Thanks in advance.

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