OSPF & Load-Balancing

[vinaymurthy]

Hi All,

I have 2-E1 links from location A to Location B. I am running OSPF in the network.

For both the serial interface i have given ospf cost as 100.

How do i configure loadbalancing on serial links which runs OSPF?

Does my configuration is load balancing?

How do i verify that OSPF is loadbalancing the links?

[paddyxdoyle · Accepted solution]

Hi,

You don't need to specifically configure OSPF to load balance, as long as both links have the same administrative distance then your peer routers will be learning the same routing information from the two different IP addresses that are on the opposite end of your E1 links.

To check whether you are load balancing your can use "show ip route".

The following example is using EIGRP however it will be similar output to OSPF with different codes and admin distance:

D 192.168.72.0/24 [90/289536] via 10.48.1.2, 1w2d, FastEthernet4/1/1

[90/289536] via 10.48.1.6, 1w2d, FastEthernet0/1/1

You can see that 192.168.72.0 /24 is being advertised from two IP addresses.

You can do per packet or per destination load balancing, i think by default on a router fast switching is enabled which means load balancing is done per destination. If you want per packet you can turn off fast switching on the interface in question using "no ip route-cache".

HTH

PJD

[amit-singh]

What paddy is saying is absolutely correct.

However caution should be taken when enabling the Per-packet loadbalancing if you have VOICE traffic going on throguh the links as packets may arrive out of order.

Per-packet loadbalacning itself is a little bit CPU intensive process so I would suggest to check the CPU utilization of router before enabling it.

I would strongly suggest to enable CEF and use the per-packet load-balancing using the interface command " ip load-sharing per-packet ".

HTH,

-amit singh