Can someone please explain why maximum legal size of ICMP echo packet is calculated as follows:
65535 - 20 - 8 = 65507
Thanks.
65535 bytes is the maximum allowed size of a IPv4 network packet, while 20 and 8 are the sizes of the IP and ICMP headers, which leaves up to 65507 bytes for the ICMP data.
来源：https://stackoverflow.com/questions/9449837/maximum-legal-size-of-icmp-echo-packet