How to do MTU discovery on Linux and Mac

To find the optimal MTU for your network, you need to find the maximum packet size you can send through it. 

on Mac  use the following command to send ping packets with a MTU size of 1500 :

ping -D -s $((1500-28)) -c 1 1.1.1.1

and on linux use:

ping -M do -D -s $((1500-28)) -c 1 1.1.1.1

To find the default MTU that is set on your device, use the following command on linux 

ip -d link list

and on mac use :

networksetup -getMTU en0

ifconfig should also show the default MTU for your network interfaces.