This section will describe a network tool that can be used for many purposes. Sometimes, this tool is called a Swiss Army Knife for TCP/IP. This tool is Netcat (http://netcat.sourceforge.net/).
Netcat is a simple utility that reads and writes data across network connections using the TCP or UDP protocol. By default, it will use the TCP protocol. It can be used directly or from other programs or scripts. Netcat is the predecessor of ncat, as described in Chapter 11, Maintaining Access. You need to be aware that all of the communication done via Netcat is not encrypted.
As a penetration tester, you need to know several Netcat usages. Because this tool is small, portable, powerful, and may exist in the target machine, I will describe ...