Probe a port with nc

Use nc to probe a port to test service availability or to check if portforwarding is working etc.

nc <hostname or ip> <port>
$ nc 22
SSH-2.0-OpenSSH_6.0p1 Debian-4

Simple Netcat Chat:

Requires 2 computers, one of which (A) must be running sshd, the other (B) must be capable of a client ssh connection. (A) must have netcat

Client (B) connects via ssh to (A)

The server (A) creates a netcat listener on any open port with:

nc -l -p 4444

Client connnects to that port with the following command issued into ssh:

nc localhost 4444

Clients and server should now be able to send plain text messages to each other via netcat. These messages are encrypted within the ssh tunnel.