Maximum Transmission Unit Determination

How to determine the maximum transmission unit (MTU) of a network link…


ping -s 1472 www.domain.tld -M do

Mac OS

ping -D -s 1472 www.domain.tld


ping -f -l 1472 www.domain.tld

How to

Normally, the 1472 should work (for MTU=1500). If not, the results will instruct about the maximum transmission unit, such as:

ping: local error: Message too long, mtu=1480

In that case, it is necessary to lower the MTU value, for example, of a tunnel interface, in iptables, etc.

Note: The static ICMP header size of 8 bytes was changed by RFC1812. Therefore, the 1472 size is just for the initial testing phase and may differ.


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