| 8.2 |  | TCP/IP Suite Control Messages |
| 8.2.1 |  | Introduction to control messages |

| The Internet Control Message Protocol (ICMP) is an integral part of the TCP/IP protocol suite. In fact, all IP implementations must include ICMP support. The reasons for this are simple. First, since IP does not guarantee delivery, it has no inherent method to inform hosts when errors occur. Also, IP has no built-in method to provide informational or control messages to hosts. ICMP performs these functions for IP. Unlike error messages, control messages are not the results of lost packets or error conditions which occur during packet transmission. Instead, they are used to inform hosts of conditions such as network congestion or the existence of a better gateway to a remote network. Like all ICMP messages, ICMP control messages are encapsulated within an IP datagram. ICMP uses IP datagrams in order to traverse multiple networks. Multiple types of control messages are used by ICMP. Some of the most common are shown in Figure . Many of these are discussed in this section.