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For example: [[File:Firebrick-1500MTU-ping.png\|200px\|thumb\|a 1500 ping on FireBrick]] On Linux: ping -c1 -M do -s 1472 81.187.81.187 On OSX (Apple): ping -c1 -D -s 1472 81.187.81.187▼ On Windows: ping -n1n 1 -f -l 1472 81.187.81.187▼ ^^ That's the ping command to remember. The rest of this section is a bit of info about that command. ==Explanation: of the ping options== '''-c1~~'''~~ In ~~these~~/ ~~examples,~~-n we1'''ve ~~only~~This ~~used~~is aoptional, ~~count~~it ofsimply ~~one~~tells ping ~~using~~just ~~the~~to -csend ~~option.~~a single ping '''-M do / -f / -D''' The important option! This means don't fragment the ping packet - we don't want the ping split into multiple packets when testing MTU! ~~'''-M do''' Use the path discovery options to ping. The option is -M. See the man page for all the options.~~ ''' -s 1472 / -l 1472''' The payload size. When setting size in ping, the size is the payload size - not the full packet size. '''The full packet size is''' <syntaxhighlight inline> payload (1472) + ~~ICMP~~IP header ~~size~~ (~~28 bytes~~20). ~~The~~+ ~~option~~ICMP ~~for~~header ~~payload~~(8) ~~size~~</syntaxhighlight>, so this is ~~-s.~~1500 in total! ~~Note: ping is slightly different on different operating systems, the above is a Debian machine.~~ ~~On OSX (Apple), to perform a ping with the same options, you can use:~~ ▲ ping -c1 -D -s 1472 81.187.81.187 ~~On a Windows machine to perform a ping with the same options, you can use:~~ ▲ ping -n1 -f -l 1472 81.187.81.187 ==Two quick examples== rtt min/avg/max/mdev = 12.491/12.491/12.491/0.000 ms So, here we ping with '''1472''' bytes, this is 1472 plus 20 bytes for the IP header and 8 bytes for the ICMP header is a '''1500''' byte MTU! Checking if you have smaller than 1500 MTU: This is despite the bridging modem used for the tests not claiming to support an MTU > 1500 octets and with PPPoE needing to send 1504 octets and receive 1508. ] [[Category:MTU]]