How to determine the optimal MTU

In a case you may need to modify the MTU size and wonder how to determine the optimal MTU for your system. You can use ping command to do so, for example, ping www.chicagotech.net -f -l xxxx, where chicagotech.net is the domain name you want to reach and xxxx is the packet size used to determine the optimal MTU for your system. For example, you can start with 1472 as showing here:

ping chicagotech.net -f -l 1472

Pinging chicagotech.net [64.176.153.103] with 1472 bytes of data:

Packet needs to be fragmented but DF set.

If the result indicates that the packet needs to be fragmented. Lower the size the packet in increments of -10 (e.g. 1462, 1452, 1442) until you have a packet size that does not fragment. Then, start increasing the packet size from this number in small increments until you find the largest size that does not fragment..

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How to change MTU

... with these default MTU settings, especially if you are using DSL line. This step-by-step article describes how to modify the default MTU size settings ...
www.howtonetworking.com/VPN/mtu1.htm