How to determine what MTU size from your networking

Zyxel_Kevin
Zyxel_Kevin Posts: 922  Zyxel Employee
Zyxel Certified Network Administrator - Security Zyxel Certified Sales Associate 100 Answers 500 Comments
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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"

image.png image.png

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

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