How to find the optimum MTU

This is something i am always forgetting so here it is, the best way to find your optimal MTU setting is to use the ping command, open your command prompt and use the following command.

ping www.google.com -f -l 1500 (lower case F and L not a 1)

you will receive something similar to this.

Pinging www.l.google.com [66.102.9.105] with 1500 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.

Ping statistics for 66.102.9.105:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

Now you need to drop the packet size down by 10 bytes until you find one that doesn’t fragment in this case it was dead on 1430 but you can increase the byte size by small factors eg 1431, 1432 etc until you find that largest possible packet for your situation.

Pinging www.l.google.com [66.102.9.103] with 1430 bytes of data:
Reply from 66.102.9.103: bytes=64 (sent 1430) time=100ms TTL=54
Reply from 66.102.9.103: bytes=64 (sent 1430) time=70ms TTL=54
Reply from 66.102.9.103: bytes=64 (sent 1430) time=64ms TTL=54
Reply from 66.102.9.103: bytes=64 (sent 1430) time=64ms TTL=54

Ping statistics for 66.102.9.103:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 64ms, Maximum = 100ms, Average = 74ms

Now you need to add 28 to the maximum size for the overhead the IP headser and the ICMP Echo Request, so I end up with 1430+28=1458 then you can use a tool like DrTCP to change the MTU value

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