Hi,
I have successfully set up an openvpn
connection and bridged it to my local network. However, I am now concerned about the
performance of the connection. The
VPN connections are made to my PC over a DSL connection from the internet to my
VPN server. The security is only
set up as a simple key and compression is not enabled.
As I am fairly new to terms such as mtu
I am not entirely sure what I should set them to. I know that the optimal mtu for my dsl connection is
apparently 1458, and when I run the openvpn program
it comes up saying the total link mtu is 1608. Presumably this a
tun-mtu of 1500 plus the 64 and 44 overheads that I
have seen are defaults. Should the mtu not be set so that the maximum it can be is 1458? If so what is the best way of doing
this. Could I use link-mtu 1458, but I have read that this is not the command to
use with TAP devices (I am running the VPNs on
Windows XP computers) or should I set the tun-mtu to 1350
which would give a total of 1458 with the overheads. Lastly should I change the values for
the overheads, I know that the 64 byte overhead can be set by the tun-mtu-extra setting and should apparently be 64 for TAP
devices, but I can’t remember where I read about the overhead that is
equal to 44 bytes.
The only reason I am concerned about the speed of the
connection is because when I ping the remote computer directly over the
internet it usually has a ping of 20ms and when I ping it over the tunnel it is
variable and anything from 30 to 70+ ms. Plus the maximum transfer rate I have
managed to get so far is about 30k/s when the DSL link is capable of 60k/s (the
DSL link is only at my end, the remote node is connected via a fast university
link, and I am trying to transfer files from the remote node to my network).
I have also read about using the ping –s command to
check for fragmentation, but ping –s on a windows pc gives you the
timestamp for count hops and doesn’t change the size of the packet.
If anybody can help me with the settings that optimise an OpenVPN link I would be most grateful.
Paul