ICMP header

ICMP header

 ICMP (Internet Control Message Protocol) is a network layer protocol for notifying communication errors and diagnosing communication status.

ICMP is in the same network layer as IP, but above it. "1" is set to the protocol number of the IP header.


 The IP protocol is an unreliable protocol. Even if a transmitted IP packet is discarded or lost, the IP protocol itself has no function to report any communication errors that have occurred.

 Therefore, ICMP was created to compensate for the shortcomings of IP. ICMP can notify communication errors and network status. ICMP messages include messages such as destination unreachable, reroute requests, time exceeded, and timestamp requests/responses.

◆ ICMP header structure

The structure of the ICMP header looks like this:

●Type (8 bits)

Represents the type of ICMP message.

-Code (8 bits)

Used with the Type message.

● ICMP Header Checksum (16 bits)

A checksum for the entire ICMP message, including the ICMP header.

Type list of ICMP header

The ICMP message types are shown in the table below. There are still many other types.

*For more detailed information, please check the link below.