Load balancing in OSPF

Unanswered Question
Mar 13th, 2007


We are having problem in OSPF load balancing. We have two links from source to destination network. We have adjusted cost of links such that in the destination network has two equal paths of equal paths. ( as seen in the show ip route command ) these paths are learned by ospf process. This is same case for other side of network. In short we have two paths of equal cost from both directions. But problem is only one link gets utilized to 90 % and another link is almost free.

Please explain !!

Thanx in advance


I have this problem too.
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Jon Marshall Wed, 03/14/2007 - 01:25


Are you doing per packet or per destination load balancing. In most cases you will be doing per destination load balancing and int this scenario you will never get equal traffic on both links.

Do you know the source and destination IP's being used. obviously one user with a big file transfer etc could utilise one of the links for a while.



Richard Burts Wed, 03/14/2007 - 08:48


Jon makes a good point about the possible impact of per destination load balancing. I believe that there is another possibility to consider. You say that you adjusted the OSPF cost to produce equal cost. This implies that the 2 links are not the same capacity. When you adjust the cost you are making OSPF believe that they are the same capacity and OSPF will treat them equally. Is it possible that the link that is at 90% is the slow link? OSPF will treat them as equal and it is logical that when the slower link is getting very busy the link with greater capacity will not be loaded as heavily.




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