8.2.1 This page will provide an overview of TCP/IP control messages.
ICMP is an important part of the TCP/IP protocol suite. All IP implementations must include ICMP support. The reasons for this are simple. Since IP does not guarantee delivery, it cannot inform hosts when errors occur. Second, IP has no built-in method to provide informational or control messages to hosts.
Unlike error messages, control messages are not the results of lost packets or error conditions that 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. ICMP uses the basic IP header to travel through 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 lesson.
The next page will describe ICMP redirect requests.
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