Network debugging tools

In this chapter you will find some tools that you can use for debugging internet socket communications applications.

• To check the status of the different ports, the machine has the "netstat" command and (only under Windows) its graphic and dynamic equivalent "TCPView" .
• To do the verification from outside the machine, we have the "nmap" tool ("Zenmap" being a graphical interface for issuing "nmap" commands and displaying them graphically results.)
• The "telnet" command is a TCP client that will allow you to establish a console link with the server of your choice and to use its services as long as you know its application protocol. You will use it to replace the TCP client in client/server communication in connected mode.
• The command "netcat" (swiss army knife of the network) allows you to act both as a client and as a server above the TCP and UDP transport layers. It was designed to allow you to replace any application in client/server communication.
• Finally "Wireshark" is a "packet sniffer" that will allow you to spy on unencrypted communications between clients and servers.