OSPF Metric adjustment

[Dakiraun]

Hi Gang

We have an interesting issue that's cropping up on our core routers. There are 3 T1 lines to another of our offices, and because of the gatway config on many workstations, a single T1 on one core (a Cisco 7507) is being preferred for most of the traffic, leaving the other core router (same hardware) and it's 2 T1s virtually unused. I was thinking I could increase the metric on the first one to make traffic prefer the other T1s. Would I be using the auto-cost and reference-bandwidth for this?

Dak

 

[macanudo]

i don't think the auto-cost reference-bandwidth will work.
my suggestion is analyzing the cost of each link and then load-balance between them, i think you're actually doing this.
you can modify the cost with 'ip osfp cost' on a per interface basis.

cheers, gabriel.

 

[Dakiraun]

Thanks Gabriel. None of the interfaces currently have a cost assigned. I can't find a reference to Cisco's default when there's no statement - do you know it? If not, I'll just go adding costs to all the interfaces for this destination across the two routers.

 

[macanudo]

cost is calculated in terms of bandwidth, actually the formula is 10^8/bandwidth i guess. you can change the formula with the auto-cost reference-bandwith command, however since ospf does not support load balancing over unequal paths what i suggest is engineer the paths so they end up with the same cost ;-)

from then on you can share the load between the routers.

hope this helps.

cheers, gabriel.