Echo Program: Principles and Applications of Software Radio Second Edition

Chapter 7 Echo Program

7.1 Introduction

The term \"ping\" originates from sonar localization operations. The ping program, written by Mike Muuss, was designed to test whether another host is reachable. It sends an ICMP echo request packet to the target and waits for a corresponding ICMP echo reply (Figure 6-3 lists all types of ICMP packets). Typically, if we cannot ping a certain host, we won't be able to Telnet or FTP into that host either. Conversely, if we can't Telnet into a particular host, it's often possible with the ping program to pinpoint where the problem lies. The echo program also measures round-trip time (RTT) to this machine as an indication of its distance from us. In this chapter, we will use the ping program for diagnostic purposes and delve deeper into ICMP. The ping program provides opportunities to test IP routing records and TimeStamp options too. Chapter 11 of Stevens [Stevens 1990] offers a source code for the echo program.