-f will mean that the ping is only sent if it isn't fragmented.

-l sets the size of the packet

ping -f 10.1.1.1 -l 1472

The reason to chose 1472 Bytes as the size for the first test is because the complete packet will then be 1500 Bytes.

Complete Packet = 20B(IP Header) + 8B(ICMP Header) + 1472B(Payload) = 1500 Bytes.

Divide and conquer method has been used to find the Max value where the ping succeeds.

Based on the above test outputs it can be seen that the ping works when size is 1372 Bytes and fails when it is 1373 Bytes.

This means only a 1400 Bytes packet will be able to reach the server and back without getting fragmented.

1372 Bytes + ICMP header 8 Bytes + IP header 20 Bytes = 1400 Bytes.