Internet Control Message Protocol (ICMP)

Fig. ICMP Header. Click to enlarge

The Internet Control Message Protocol goals and features were outlined in RFC 792 as a way to provide a means to send error messages for non-transient error conditions, and to provide a way to probe the network in order to determine general characteristics about the network.

A more accurate definition of the Internet Control Message Protocol goals and features might be that it is used for two types of operations:

• When a router or a destination host need to inform the source host about errors in a datagram processing, and
• For probing the network with request & reply messages in order to determine general characteristics about the network.

The ICMP protocol has two types of operations; therefore its messages are also divided to two:

• ICMP Error Messages
• ICMP Query Messages
  

The Internet Assigned Numbers Authority (IANA) has a list defining the ICMP message types that are currently registered. It also lists the RFC that defines the ICMP message. The list is available at: http://www.isi.edu/in-notes/iana/assignments/icmp-parameters.