Problems with TCP connections inside OpenVPN Tunnel

Bernhard Dick

Hi,

currently I see big performance problems with TCP connections within an
OpenVPN tunnel. The OpenVPN server is connected via UMTS, on that
connection I get about 2MBit UL and 10MBit DL rate.
Inside the tunnel I get a quite good download speed (client -> server),
the upload speed (server -> client) however is terrible, iperf gets
about 30-80 KBit/s the tunnel via TCP. UDP traffic inside the tunnel is
nearly at the speed of the UMTS connection.
With wireshark I see a lot of TCP retransmissions on the tunnel
interface, most of them leading to duplicate ACKs. Tcptrace shows me a
RTT of about 800ms inside the tunnel, ICMP requests however are showing
about 70-80ms.
The problem is independent of the OpenVPN connection type (udp or tcp)
being used. I also experimented with the fragment, mssfix, tun-mtu and
link-mtu siwtches, they didn't help either.
Do you have any ideas how to improve the TCP performance?

Traffic

What version of OpenVPN do you use ?

Bernhard Dick

Hi,
on the server side I'm using OpenVPN version 2.1.1. The client is running OpenVPN 2.3.0.
Btw I'm not sure, if I have used the correct forum, if this board is not for the OpenSource version please move this thread to the correct location.

Bernhard Dick

The OpenVPN Server is running version 2.1.1, on my client I am running OpenVPN 2.3.0.
Btw I'm not sure, if I posted in the correct forum as I am using the OpenSource edition. So please move this thread if it is in the wrong area.

Bernhard Dick

Hi,
just a short note. The problem is solved. It was not OpenVPN related, there was a bug in the used linux kernel causing the TUN device to be very unperformant.

Regards
Bernhard

Traffic

Thanks for your reply .. sorry moderating post has been taking so long.

FYI:

Bernhard Dick wroteThe OpenVPN Server is running version 2.1.1, on my client I am running OpenVPN 2.3.0.

You should probably consider upgrading these ASAP and recreate your PKI just in case of heartbleed ..