Maximum legal size of ICMP echo packet

Question

Can someone please explain why maximum legal size of ICMP echo packet is calculated as follows:

65535 - 20 - 8 = 65507

Thanks.

Biota

Answer 1

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.

Ragland

Correct me if I'm wrong, but maximum size of IP header is 60 bytes (20 is minimum). Isn't it correct to get the size of the data for the ICMP echo packet based on the "65535-60-8" instead? Or I am missing something? – Hetero

@Hetero if you want the maximum size of the ICMPv6 echo packet you want the smallest IPv6 header to get the largest ICMPv6 packet possible in what remains of the max MTU. – Goulette