1. All ICMP packets have an 8-byte header and variable-sized data section.

2. For example, ICMP will send a source quench message when traffic becomes congested at a router.

3. The various implementations of traceroute all rely on ICMP Time Exceeded (type 11) packets being sent to the source.

4. Aping is a command line ICMP echo (ping) utility optimized for reliable high performance monitoring of large numbers of systems

5. The first 4 bytes of the header have fixed format, while the last 4 bytes depend on the type/code of that ICMP packet.