netcat

Listen, connect, ...

Basic command to listen on a TCP/UDP port:

TCP

$ nc -l -p <port>
$ nc -lp <port> # or simply

# eg. listen on local address TCP port 8000
$ nc -lp 8000

UDP

$ nc -u -l -p <port>
$ nc -ulp <port>

# eg. listen on local address UDP port 8000
$ nc -ulp 8000

Flags:

1. -l: listen mode, for inbound connects

2. -p: local port number

3. -u: UDP mode

Connect to TCP/UDP server at a port

Connect to a TCP server:

$ nc <address> <port>

# eg. connect to TCP server at 88.88.88.88 port 8000
$ nc 88.88.88.88 8000

Connect to a UDP server:

$ nc -u <address> <port> 

# eg. connect to UDP server at 88.88.88.88 port 8000
$ nc -u 88.88.88.88 8000

nc(1): arbitrary TCP/UDP connections/listens - Linux man pagelinux.die.net