# ICMP [ICMP](https://en.wikipedia.org/wiki/Internet_Control_Message_Protocol) is defined by [RFC 792](https://datatracker.ietf.org/doc/html/rfc792). Headers are 8 bytes; the first 4 bytes have a fixed meaning, while the meaning of the last 4 bytes varies depending on the type of request specified in the first 4 bytes. ICMP traffic "types" correspond to the kind of packet being sent (though different ICMP services can have multiple types): - 0 - Ping reply - 8 - Ping request Ping packets typically just include either random data or all zeros.