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Webcast-Catalyst9k
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unequal cost load balancing

Can anyone tell me how I achieve this, I know you can add a cost at the end of the route, but I thought this is used for redundancy ?

thanks

Carl

2 REPLIES
Purple

Re: unequal cost load balancing

Hi Carl,

Cisco routers will automatically load balance if you have more than one equal-cost route to the same destination. For example, say you had 2 static routes:

ip route 10.1.1.0 255.255.255.0

ip route 10.1.1.0 255.255.255.0

In the above case, IOS will install both routes into the routing table and load-balance over them. The type of load balancing wil depend on the type of swiching mechanism used by the router:

process switching - per-packet load-balancing

fast switching - per-destination load-balancing

CEF switching - per-destination or per-packet load-balancing

With routes learned by routing protocols, they have to have the same administrative distance and metric to be considered equal.

Hope that helps,

Paresh

PS. Pls rate helpful posts.

Purple

Re: unequal cost load balancing

Whoops.. looks like I answered the wrong question here.

Okay, the only protocols that support unequal-cost load balancing on Cisco routers are IGRP, EIGRP and BGP. For IGRP and EIGRP, you have to specify the variance parameter, which indicates that the maximum metric a route can have compared to the best metric for it to be considered a candidate for unequal-cost load balancing. For example, if the best route has a metric of 100 and there are two other routes to the same destination with metrics of 150 and 250 respectively, a variance of 2 will mean that the routing with the metric of 150 will also be installed in the routing table. This is because 150 < 2*100.

With BGP, you can achieve unequal-cost load balancing using the dmz-link bandwidth extended community.

Hope that helps,

paresh

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