Poor performance with iperf3 and OpenVPN under Windows 10

gabemorgath · Post by **gabemorgath** » Mon Apr 23, 2018 11:45 am

Hi to everyone.

As the title says, i'm doing some tests with OpenVPN and a VPS (Ubuntu Linux version 16 LTS) with 1gigabit port (both directions). My ISP connection has around 160Mbit in down and 20Mbit in up.

If i launch a speedtest while the VPN is active from my client (Windows 10 1803 build 17133.1) i have very poor performance: at the beginning of my tests i was reaching a super slow speed: about 20mbit in down. After some research and tweaking with openvpn configurations i managed to reach about 40 mbit in down which is still not enough. There is absolutely something wrong so i continued with experiments: i decided to give a try to the connection between me and the vps without going through the vpn. In this scenario the result with iperf3 is super clear: the connection between me and the vps is capped at around 50mbit. After some other tests and research, i got a doubt and i decided to try everything under a linux distro. So i ran an ubuntu live session on the same pc client i was using before and, big surprise, everything work as expected: i can reach max speed (around 160Mbit) in both iperf3 and openvpn. So, finally, i realized that the problem is something under Windows 10 indeed. I already tried with different settings of Autotuning level under the tcp/ip settings with no luck: the max speed i can reach is always 50mbit. The strange thing is that if i try to download something else from the vps (with chrome for example with http) i can get full speed instead: the only problems seems to be with openvpn and iperf and seem to be connected. Any clue about this? Thank you!

Post by **Philip** » Mon Apr 23, 2018 1:13 pm

Try to set your MTU down to ~1200 bytes and see if that helps?

I think the correct way is to first set in in Windows (you can use the TCP Optimizer), then also add the following to the vpn.conf on both ends (increases send/receive buffers as well):

Code: Select all

fragment 1200
mssfix 1200


sndbuf 2000000
rcvbuf 2000000
txqueuelen 4000

You should also try UDP vs. TCP...
Someone reported this MS security update also caused issues with openvpn --> KB 4074588 (It has something to do with driver signing for USB and TAP adapters). Uninstalling/reinstalling the TAP adapter may help with this also, not sure.

Also, you may want to try an older TAP adapter driver, there is some issue with the latest driver I believe.

gabemorgath · Post by **gabemorgath** » Mon Apr 23, 2018 1:33 pm

Thank you for reply. I will try with those settings and report it back. And what about the iperf3 test? It's also limited to 50mbit.

UPDATE:

I've tried your config but i get even worst performance.

The option

txqueuelen 4000

makes the openvpn client crash on start. I already tried tcp and udp but still nothing.

Post by **Philip** » Tue Apr 24, 2018 7:48 am

Not sure about the Iperf3 limitation, could also be driver related/Windows build related (you may have to pass more parameters to it specifying larger TCP Window, etc.).

Have you tried the TCP Optimizer?

gabemorgath · Post by **gabemorgath** » Tue Apr 24, 2018 8:38 am

Yeah, already tried tcpoptimizer but without luck: always same results.