ICMP, Internet Control Message Protocol, is a networking protocol. Its purpose is to pass on error messages (such as “unreachable host”) and informational messages (such as ping requests and responses), rather than application data.

Current RFC

Similar to the Internet Protocol (which has a number, RFC 791, exactly one less than this one), the original document refers to just “ICMP” rather than “ICMPv4”. ICMPv6, described below, follows different rules.

Additions and Deprecations

Current ICMPv6 RFC

There are two older versions of the specification:

ICMP Parameter Numbers

IANA also maintains the lists of parameter numbers for ICMPv4 and parameter numbers for ICMPv6.