6509 RSM load balancing

[nkhwaja]

Here is our setup. One RSM connected to two 7xxx routers at both ends of ATM circuits.

6509 RSM |---->7204----ATM circuit 4Mb ------<--7206----| RSM 6509

|----->7206---ATM circuit 4 Mb-------<-7204----|

We notice poor load balancing between the two ATM circuits - traffic at any time is double on one circuit although 'sho ip route' shows equal routes, metrics.

Any suggestions ??

[rsissons]

Although IOS will automatically load balance over, up to 4, equal cost paths, it will balance on a per session, rather than on a per packet basis so you will not necessarily see equal utilisation.

You can force the router to loadshare on a per packet basis by disabling fast switching, ie 'no ip route-cache' on the interfaces, however this is NOT recommended as it will impact the performance of the router.

[nkhwaja]

1. theres a large difference in the traffic on two circuits. Is Session = pair of source+destination always??

2. Secondly is RSM a good choice in this config or a router should be used instead ? I remember reading that RSM does not perform as good as a router for WAN traffic ???????.