When IPv4 or IPv6 sends an ICMPv4 or ICMPv6 error message, it includes the IP header of the packet that caused the error message. This parameter controls how many extra bytes of the packet beyond the IPv4 or IPv6 header are included in the ICMPv4 or ICMPv6 error message.
8 to 65,536 bytes
Do not change the value. Including more information in an ICMP error message might help in diagnosing network problems. If this feature is needed, increase the value.