UDP Packet loss

Hey guys,

Wondering if someone can shed some light as to what is going on here. I have found this issue with multiple clients and I don't understand what is causing this. The usual complaint is slow UDP connections (usually to a SQL server). I don't see this problem when source/dest are on the same subnet, this only occurs when a router is involved (usually a cisco). I have tested this every way i can possibly think of and all yield the same results; 0% packet loss in one direction, >30% packet loss in the other direction. Many times its 99% packet loss at 100Mbit. I have tested this on multiple workstations, servers, virtual hosts, network cards, as to eliminate them as a potential cause. All yield the same results.

In the test below ..
Server is connected at 1Gbps, Workstation is 100Mbit.
Server is 192.168.30.5
Workstation is 192.168.40.75

The two pictures below show the server and client side of iperf. 192.168.30.5 acting as the iperf server. Reversing iperf server / client has 0 impact on the results.

First test: Send from 192.168.40.75 -> 192.168.30.5 = 0% packet loss @ 50Mbit
Second test: Send from 192.168.30.5 -> 192.168.40.75 = ~35% packet loss @ 50Mbit

If i bump the test up to 70Mbit:
First test: Send from 192.168.40.75 -> 192.168.30.5 = 0% packet loss @ 70Mbit
Second test: Send from 192.168.30.5 -> 192.168.40.75 = ~43% packet loss @ 70Mbit


Any ideas as to why one direction 0% packet loss while the other direction on the exact same network >35%.

Just to add, TCP has no problem and will max the connection without issue.

Thanks!