netcat is a command for performing read/write operations on TCP or UDP network connections.
From the official GNU netcat project page:
It is designed to be a reliable "back-end" tool that can be used directly or easily driven by other programs and scripts. At the same time, it is a feature-rich network debugging and exploration tool, since it can create almost any kind of connection you would need and has several interesting built-in capabilities.
It provides access to the following main features:
- Outbound and inbound connections, TCP or UDP, to or from any ports.
- Featured tunneling mode which allows also special tunneling such as UDP to TCP, with the possibility of specifying all network parameters (source port/interface, listening port/interface, and the remote host allowed to connect to the tunnel.
- Built-in port-scanning capabilities, with randomizer.
- Advanced usage options, such as buffered send-mode (one line every N seconds), and hexdump (to stderr or to a specified file) of trasmitted and received data.
- Optional RFC854 telnet codes parser and responder.
SANS has produced a netcat cheat sheet (PDF) with various tips on usage.
