How to determine what MTU size from your networking

Zyxel_Kevin

First of all you may know ICMP header is 28 bytes.

Then using ICMP with Don't Fragmented parameter to find your network MTU.
Here is example for Macbook command:

The icmp request can not be sent while length exceed 1473 byte, the message said "Message too long"

Which means the exact MTU size is 1472+28(icmp header) = 1500