Interpretation of MTU-Test Result

Virtual Private Networks OpenVPN
1

Hello,

i made the MTU-Test in OpenVPN to optimize the tunnel.
I used the wiki page wiki.ipfire.org - Troubleshooting
with the chapter MTU-Test.

Wiki Page:
In this test the value is suggested by OpenVPN ​​to 1253 to what can be achieved if 1253 will be written into the “fragment” line into the web-interface, also mssfix should be activated, the actual MTU value can be left in 1500.

My Test Results
NOTE: Empirical MTU test completed [Tried,Actual] local->remote=[1700,1604] remote->local=[1684,1636]
What is the correct value for the optimal MTU ?
With the example iam not able to understand the result

NOTE: This connection is unable to accommodate a UDP packet size of 1700. Consider using --fragment or --mssfix options as a workaround.

I can use the Value direct as MTU Size or / and as fragment (MTU 1500 + Fragment X)

Thank you

2

Found in my notes from long time ago … if it helps.

# calculate optimal MTU
#
`size=1272; while ping -s $size -c1 -M do google.com >&/dev/null; do ((size+=4)); done; echo "Max MTU size: $((size-4+28))"`
3

Hi,

thank you.
My problem is more what to place in the fields
“MTU” and “fragment” in the Ipfire OpenVPN config.

4

I have 1500 in the mtu and fragment is blank, my vpn works well.

5

i optimzed ones the MTU with the meassure. (speed and performance went up to 50%)
But the result was like in the Wiki,
now i have different values and i dont know what values i have to add.

1500 is the wrong size for me.

6

Can you try 1400 ?