CEF load Balance

Unanswered Question
Dec 5th, 2007

Is cef per-destination load balance is two ways?

Meaning if I have 2 links between site A and Site B and both are using cef per-destination load balance, will soure-destination pair used for load balance between site A and site B, will be the same as from Site B back to site A.. Or it might result Asymmetrical routing

I have this problem too.
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bvsnarayana03 Wed, 12/05/2007 - 07:21

Probably this is based on the cost of the paths. As I read from other posts, CEF populates FIB table by taking entries from routing table. So FIB will have interface against prefix, & this interface will be the 1 with the best cost to destination.

So if the pkt coming from interface doesnt have the best cost for return traffic then there may be case of asymetry.

royalblues Wed, 12/05/2007 - 07:23

I dont think it will be.

But it does not cause any problems as per destination makes sure a flow is maintained via one link. So it could be quite possible to see that the originating session takes one route and the return traffic takes the other route

you can do a quick check on this by issuing the command

sh ip cef exact-route

try these commands on both ends for multiple source destination pairs and see whether they end up on the same link

HTH

Narayan

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