Speeding up your OpenVPN tunnel

Here are some settings to speed up the transmission rate through your OpenVPN tunnel:

  • proto udp
  • mssfix 0
  • fragment 0

mssfix: Even though MSS itself is a TCP feature, this OpenVPN option targets encapsulated UDP packets. It will change the MSS value of the TCP protocol inside the tunnel in such a way that after UDP encryption/encapsulation, the resulting UDP packet size (minus IP/UDP headers), will not exceed the mssfix value.
By setting the value to 0, we disable this feature.

fragment: This will disable OpenVPN’s internal fragmentation routines (OpenVPN 2.x actually does this by default).

Another improvement is raising the MTU (Maximum Transmission Units), which is the maximum datagram size in bytes that can be sent unfragmented over a network path.

First make sure your OpenVPN server has set the same MTU size:

ip link set eth0 mtu 9000

Next, add this to your OpenVPN configuration:

tun-mtu 9000

By jochen

Developer at TestingBot and Tinder