unequal ip cef load balancing

jigsaw2026 · ‎03-19-2007

I have a 3750 (a) at a branch office connected to 2 3750s (b, c) at head office via 2 x LES10s (vlan 10 and vlan 20). 3750 c handles routing and is connected to 3750 b via a trunk link. So vlan 10 runs a > c, while vlan 20 runs a > b > c.

I am facing a problem on 3750 c in that it does not load balance traffic across the 2 links - vlan 10 is only using 0.12% tx, whilst vlan 20 recives 36% of the traffic.

-routing is via EIGRP, only one subnet attached to 3750a, both routes in r-t

-show ip cef shows per dest load balancing

-packet sniffing on vlan 10 reveals that there's only 3 src-dest pairs' traffic running on it.

-show ip cef internal shows load-bal with 16 hash buckets evenly distributed.

There is a terminal server attaced to 3750a which a lot of people attached to c connect to, other than that there is a fairly wide spread of destinations. However, when I use source-dest pairs found with packet sniffer, and run on 3750 c show ip cef exact-route <src> <dst> about 25% of entries (on both links) should be using the other link according to the output.

Does anyone have any thoughts on this? Any help would be gratefully recieved.

Many thanks,

J

glen.grant · ‎03-19-2007

See if this might help . http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuration_guide_chapter09186a00800ca7cc.html#wp1000978

jigsaw2026 · ‎03-20-2007

Thanks, interestingly the various per-dest load balancing options make no difference to amount of traffic being sent over each link.

jigsaw2026 · ‎03-20-2007

For anyone interested - it was because I had fair-queueing set on the problem vlan interface on 3750 c. Once I removed this, traffic has been (approx) evenly distributed since.

Not sure why this would be though!