loading balancing

Unanswered Question
Jul 9th, 2007


We have two WAN links (E1 and 1M). how can we config load balancing? e.g. two packets go E1, one packet goes 1M.


Best regards

I have this problem too.
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Jon Marshall Mon, 07/09/2007 - 09:27


What routing protocol (if any) are you using. Eigrp for example can do unequal cost load-balancing but OSPF cannot.


minumathur Mon, 07/09/2007 - 09:58


First of all you need to use EIGRP routing protocol , which support unequal load balancing. after that you can use "maximum path 2 " command in configuration.This will load traffic sharing.

i would suggest to you to use policy base routing, i.e mean some traffic will go to specific link and other traffic go to specifc link, I hope this will clear your point.

Please rate this post.


Richard Burts Mon, 07/09/2007 - 10:23


Your comment about treating both links the same (if one is 1 MB, other link is also 1 Mb, so rest of bandwidth are not in use) would be true if the load balancing were based on static routes or on manipulating OSPF metrics to make both paths look equal. But with EIGRP unequal load balancing the traffic will be shared proportional to the bandwidth of each link.



Paolo Bevilacqua Mon, 07/09/2007 - 11:43

Hi Rick,

have you ever implemented "EIGRP unequal load balancing" in a real network, and have it running ?

If so, could you share with us some "show" commands like "interface", "route", "ip cef adjacency" ? The more detail, the better.

As you may have read from other threads, I'm personally very dubious about the working of it, but if it can be proven otherwise to me, I will be happy to learn about it.

NB: I find the low rating on your post above very inappropriate for a serious discussion made in the best intent by anyone.

Richard Burts Mon, 07/09/2007 - 12:03

Hi Paolo

I do not currently have anything running EIGRP unequal load balancing. I believe that I have had it running (and thought it was running correctly sharing load on both links) but that was a long time ago. And frankly I am not enthused about this aspect of EIGRP.

I believe that many people have problems trying to get unequal load balancing to work because they do not pay attention to the detail that the second link must qualify as a feasible successor. In many cases they have a wide difference in capacity between the links and think that if they make variance large enough that it should load balance. But with very large capacity differences it is difficult to get feasible successors.

Thanks for your comment about the rating. I was surprised and disappointed by the low rating, especially since it was only a small correction to someone else's post. But I figure that is part of being a publically rated system.



Paolo Bevilacqua Mon, 07/09/2007 - 12:49

Hi Rick,

In fact I remember a long time ago, I was tinkering with EIGRP and wanted to try "unequal load balancing", the feasible successor issue came up, and required special tuning. Honestly I don't remember if the routing as set like that, was bringing any practical advantage.

Then I didn't touched anymore that particular network, and for the following 10 years, most of them spent working at cisco, I haven't heard of anyone using the feature with any success, actually quite the opposite. I've hence happily adopted this position.

What puzzles me most about it, is that I don't see a provision for unequal load sharing in CEF, that is ultimately responsible for actual packet switching, while EIGRP is only in the control plane and cannot influence it directly.

Wrt the rating, we already know that occasionally someone that that disagrees, isn't happy with the answers, or simply don't understand it, misuses the system.

Anyway, your contribution is very much appreciated and I invite you to keep up with the good work here!

Richard Burts Mon, 07/09/2007 - 13:31


I have not thought much about the interaction with CEF but a long time ago I had much the same question about how it did unequal load share since EIGRP puts routes into the routing table and some other process is making the forwarding decision. When I asked about it I was told that the traffic share parameter was used for this. I am not sure if that has some interaction with CEF.

Thanks for the kind words. I hope that we both continue to be active and to keep up the good work.




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