Lower than possible MTU is suboptimal, higher is flaky and may break networking completely. How to find the right value?
Here’s a slightly time intensive way that uses a tool you should already have at hand, ping.
ping -M do -c 8 -v -n 220.127.116.11 -s 1464
Ping sends a packet across the network and lets you know how quickly it go there. Here to find the “maximum transfer unit” (MTU) we adjust the size of the packet and check to see if it needs to be broken up (“fragmented”) in order to travel over the network.
You basically want to adjust the 1464 until you get the highest possible number that doesn’t produce a warning/error stating that fragmentation is needed. For me, setting “-s 1600” (or anything over 1464) I get for example:
From 192.168.1.2 icmp_seq=1 Frag needed and DF set (mtu = 1500)
as lines in the ping output (emphasis added).
MTUs vary a lot. I’d start with 1400, try 1500; if you’re above 1500 or below 1400 then try double/half, other wise do interval bisection to find the best value. There’s nothing especially wrong with a lower value than you’re capable of setting successfully it’s just that it will be slightly less optimal.
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