[Cialug] Linux router causing me some trouble

[Jonathan C. Bailey]

I've been banging my head against the wall for the past few hours with a routing performance issue.. Here's the test configuration:

testserver (physical host) <-----gigabit wired network-----> eth0 troublerouter (Ubuntu 10.04 VM) eth1 <-----private vSwitch-----> testclient (Ubuntu 10.10), testclient2 (XP SP3)

Test methods:
  SpeedTest mini (on testserver)
  iperf (Server: iperf -s -l 1024k / Client: iperf -c SERVER -l 1024k -P 10)

Only configuration on troublerouter:
  * Disabled IPv6 (ipv6.disabled=1 passed to kernel)
  * Masquerade rule: iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

Test results:

testserver <-> troublerouter with iperf: ~900mbit
troublerouter <-> testclient with iperf: ~9gbit
testserver <-> testclient with iperf: ~2mbit
testserver <-> testclient with speedtest mini: ~200mbit down, hangs on upload
testserver <-> testclient2 with speedtest mini: ~200mbit down, hangs on upload


I ran wireshark to look at things, and I see multiple fragmentation needed messages (everything is 1500 from end to end), but that's about it. I tried setting the MTU to 1400 in the test clients and that didn't help. Any ideas? Thanks!


-Jon