netcat – a Unix utility that allows you to establish TCP and UDP connections, receive data from there and transmit them. Despite its usefulness and simplicity, this utility is not included in any standard.
To check the availability of TCP / UDP ports on a remote machine, we will use the Netcat utility
Under Windows, this utility is also available
Checking the TCP port
$ nc -zv 10.10.4.4 22 srv-app.local [10.10.4.4] 22 (ssh) open
Checking the UDP port
$ nc -uv 10.10.4.2 123 srv-dc01.local [10.10.4.2] 123 (ntp) open