Load-balancing using CEF

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Oct 1st, 2002
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Good Day,


We have two links with two different backbones to Internet and we want to load-balance the traffic between these two links.

We can't use BGP to do that, so we are using CEF.

It seems that the CEF doesn't load-balance correctly !

What's going wrong ?


Thanks in advance.


Fethi.

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donewald Tue, 10/01/2002 - 10:21
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Fethi,


CEF is designed to load share based on equal cost routes that it gets from whatever routing protocol you are suing and does so using several methods (per dest, per packet) depending on how you configure it. Can you be more specific with your problem with CEF. Here is an outstanding link on how to configure and verify load sharing is working correctly.


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


Hope this helps you,

Don

swpowell Tue, 10/01/2002 - 11:39
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Without BGP, you cannot load balanc inbound traffic. However, you can load balance outbound traffic by setting up two default routes, one to each ISP router. The router will use a round-robin approach when transmitting packets. This can be done with any number of links, as far as I know. I current do this one two different routers with 2 T-1's each.

lwantland Wed, 10/02/2002 - 04:56
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Actually, CEF does not load balance in a round robin fashion. You can use CEF to load balance on a per destination, or per packet basis. Per packet can cause problems with out of sequence packets, so I always user per destination. In this mode, CEF builds switching tables based on the source & destination IP addresses. Some will take route 1, and some will take route 2. The important difference is, until there is a change in topology all packets with the same source & dest will always take the same link. This is different behavior from other protocols or dual static routes which do use round robin. As a rule, if you links are close to each (about 20% difference or better) other in outbound traffic, CEF load balancing is working just fine.


Regards,

Lance Wantland


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