#4 UDP iperf application drops


I have the following testbed setup:

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desk-PC Ixia M7i-router PC-laptop

My Ixia traffic generator is generating 2 different traffic streams totaling 25Mbps and sending to M7i-router.

Both PC's are running freeBSD 6.2

Iperf client is running on desk-PC and Iperf server is running on PC-laptop
I am sending 25Mbps of UDP port 5001 for 60 seconds to PC-laptop. So the Ixia generated traffic and this iperf traffic is going through the Cisco 3745. After the test is done, I always get ~15% loss reported by Iperf. Cisco shows no drops at all. TCPdump on the desk-PC show that I am sending the same amount of packets being received on laptop-PC. So we know that all of the packets are arriving at the server, but the Iperf tool is reporting loss still.

I assume there's some kind of threshold that is being exceeded? Can we configure some kind of threshold in Iperf?

When I replace the cisco router with a Juniper J6300 router, the same results are seen except the application loss is ~8%. Via tcpdump being run on both PC's, we can see all packets arrive on the server that are being sent, but the Iperf app is reporting loss. We have both FreeBSD PC's synch'ed via NTP to the same server. When I stop Ixia traffic and run just the Iperf test at 25Mbps, then there is no loss reported. This also points to some kind of threshold being exceeded in Iperf.

I appreciate any feedback.