TCP/IP First-Step [Electronic resources] نسخه متنی

Chapter 10. Special Delivery for Special Messages

What You Will Learn

By the end of this chapter, you should be able to answer the following questions:

What does the acronym ICMP stand for?

Which layer of the OSI reference model does ICMP occupy?

What is the purpose of ICMP?

Is ICMP useful to end users?

What are some of the tools that you can use that rely upon ICMP?

What does PING do and why is it useful?

Which ICMP message types does PING utilize?

What does TRACEROUTE do and why is it useful?

Which ICMP message type does TRACEROUTE utilize?

Can the use of a system communications mechanism such as ICMP make IP a reliable protocol?

After having seen that TCP/IP offers two options for data deliverybest effort by UDP and reliable delivery by TCPyou might be wondering what else you could possibly need in a communications protocol! The answer is simple: You still need a mechanism for delivering system messages.

System messages are a bit different than the types of applications discussed in the previous two chapters. Instead of originating at a user machine, system messages originate inside the network. User applications let users communicate with each other, share data, run application software, and so on, but system messages let the network devices communicate, coordinate their activities, and actually run the network. The mechanism that transports these special messages is the Internet Control Message Protocol (ICMP).

ICMP is designed to transport system-level messages between network devices. Generally speaking, ICMP helps disseminate information about error conditions between systems and network devices in an IP network.

In this chapter, you take a look at ICMP, its mechanisms and how they work, and the role that this transport protocol plays in a network. You find that ICMP plays an interesting and critical but behind-the-scenes role in an IP network's normal operation.