unequal cost load balancing

[carl_townshend]

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

[pkhatri]

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.

[pkhatri]

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