Internet Control Message Protocol

What Does Internet Control Message Protocol Mean?

Internet Control Message Protocol (ICMP) is a TCP/IP network layer protocol that provides troubleshooting, control and error message services. ICMP is most frequently used in operating systems for networked computers, where it transmits error messages.


ICMP for Internet Protocol version 4 is called ICMPv4 and for Internet Protocol version 6 is called ICMPv6.

Internet Control Message Protocol is also known as RFC 792.

Techopedia Explains Internet Control Message Protocol

An ICMP message is created as a result of errors in an IP datagram or for diagnostic routing purposes. These errors are reported to the originating datagram’s source IP address. An ICMP message is encapsulated directly within a single IP datagram and reports errors in the processing of datagrams.

An ICMP header begins after the IPv4 header. An ICMP packet has an eight-byte header, followed by a variable-sized data section. The first four bytes of the header are fixed:

  • ICMP type
  • ICMP code
  • Checksum of the entire ICMP message
  • Checksum of the entire ICMP message

The remaining four bytes of the header vary based on the ICMP type and code.

The error message associated with ICMP includes a data section that holds the entire IP header along with the first eight bytes of the packet that generated the error message. An ICMP datagram is then encapsulated in a new datagram.


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Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.