Chapter 8

Internet Control Message Protocol

Abstract

In this chapter, you will learn about ICMP messages, their types, and (in many cases) the codes used in each type. We’ll look at which ICMP messages are routinely blocked at firewalls and which are essential for proper device operation.

You will learn about the common ping utility for determining device accessibility (“reachability”) on an IP network. We’ll discuss the mechanics of both ping and traceroute, and use several ping examples to illustrate ICMP on the network.

Keywords

ICMP; control messages; ping; traceroute; reachability

What You Will Learn

In this chapter, you will learn about ICMP messages, their types, and (in many cases) the codes used in each type. We’ll look at which ICMP messages ...

Get The Illustrated Network, 2nd Edition now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.