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

Installation:

                      
                        ### 
                        
                          CentOS
                        
                        
$ sudo yum install nc


### 
                        
                          Debian
                        
                         / 
                        
                          Ubuntu
                        
                        
$ sudo apt update
$ sudo apt install netcat
                      
                    

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