The Internet Control Message Protocol, or ICMP, described in RFC 792, specifies a variety of messages
whose common purpose is to manage the internetwork. ICMP messages may be classified as either error
messages or queries and responses. Figure 2.28 shows the general ICMP packet format. The packets are
identified by type; many of the packet types have more specific types, and these are identified by the code
field. Table 2.5 lists the various ICMP packet types and their codes, as described in RFC 1700.