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Load balancing unequal cost paths with OSPF - (yuk)

Hi, I have a dilemma I'd like some input on:

I have a distibution layer Router A with an OC-3 (155Mbps) link to a core layer BGP-speaking Router B. Currently, all traffic to and from router A goes out Router B. However, I also have a 1Gbps link from Router A to Router C, another distribtion layer router, whcih in turn has a 1Gbps link to a router D, which will soon also run BGP. And OSPF is our IGP :)

Dilemma: I want to send approx50Mbps traffic from Router A to Router D. But OSPF does not allowload sharing over unequal cost paths. Anyone know any other way around this? I really don't want to reconfigure my routing protocol to EIGRP. I thought about creating a route-map to match some subnets off Router A, and setting a conition to make them more attractive to Router D. Any input is appreciated :)

2 REPLIES
New Member

Re: Load balancing unequal cost paths with OSPF - (yuk)

Brett:

If the destination of the traffic is internal to your network, then you're stuck. :-(

When you mention that router D "will soon also run BGP", what do you mean?? If you mean that the destination of the traffic will now be external to your network, then you could use the Link BW community and iBGP multipath to share the load. for more on this, take a look at: http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1829/products_feature_guide09186a008012db46.html

Alvaro.

Silver

Re: Load balancing unequal cost paths with OSPF - (yuk)

Actually, you may not be totally stuck... if the need is solely to load balance outbound traffic coming into router A. What you do is fudge the metrics on the routes so that the path A to C to D has the same total metric as the path A to B. Note that this will have no impact on traffic coming back from the Internet and will have the side effect of forcing all outbound traffic hitting router C to go strictly to router D (unless, of course, that route fails, in which case all traffic will go out through B.

Of course, the "correct" solution is to put pressure on your sales rep to have Cisco provide unequal cost load sharing with OSPF. There is no technical reason to not do so (indeed, OSPF is even better than EIGRP at identifying loops). The problem, of course, is that there are marketing reasons to provide EIGRP with as many advantages over OSPF as they can get away with.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

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