Airvpn and MTU size

[Valunker 0]

The MTU Size for me is 1460, I read this article http://www.tp-link.us/FAQ-190.html and its mentioned there "Due to additional complications, VPNs require a different type of MTU test."

https://community.spiceworks.com/topic/217130-mtu-issues-in-vpn-connections

So do I have to use different MTU than the usual if yes then how do I find the correct MTU for airvpn

[Valunker 0]

I checked for MTU after connecting to one of the airvpn servers.

ping www.google.com -f -l 1472

1472 + 28

1500 turned out to be my MTU when I was connected to the VPN when I am not connected to the VPN the MTU is lower ?
Should I use 1500 in my router MTU setting or the usual MTU when I am not connected to the VPN.
 

[go558a83nk 352]

If you have a DSL connection you should use 1492 in your router.  Otherwise 1500 should be used.

[OpenSourcerer 1360]

Disconnect from the VPN and do the tests again. TCP Optimizer for Windows has got a nice feature to determine the max MTU for you. Assuming it will show you 1500, it means for UDP:

Max size - IP header = 1472 bytes.

Max size - (IP header + OpenVPN header) = 1392 bytes.

 

If you lower the MTU, say, by 28 bytes, you get a lower size in both scenarios which wouldn't be your max:

(Max size - 28 bytes) - IP header = 1444 bytes

(Max size - 28 bytes) - (IP header + OpenVPN header) = 1364 bytes

 

Ergo, don't worry about MTU, just use your max. If you use Windows, I recommend starting the program above with admin rights and do the TCP optimizations for your download speed. Windows' defaults are not the best.