How to Check Remote Ports are Reachable Using ‘nc’ Command?

A port is a logical entity which acts as an endpoint of communication associated with an application or process on a Linux operating system. It is useful to know which ports are open and running services on a target machine before using them.

 

netcat (or nc in short) is a powerful and easy-to-use utility that can be employed for just about anything in Linux in relation to TCP, UDP, or UNIX-domain sockets.

 

We can use it to: open TCP connections, listen on arbitrary TCP and UDP ports, send UDP packets, do port scanning under both IPv4 and IPv6 and beyond.

 

Using netcat, you can check if a single or multiple or a range of open ports as follows. The command below will help us see if the port 22 is open on the host 142.68.18.1:

$ nc -zv 142.68.18.1 22

 

In the command above, the flag:

  • -z – sets nc to simply scan for listening daemons, without actually sending any data to them.
  • -v – enables verbose mode.

 

The next command will check if ports 80, 22 and 21 are open on the remote host 192.168.5.10 (we can use the hostname as well):

nc -zv 142.68.18.1 80 22 21

 

It is also possible to specify a range of ports to be scanned:’

$ nc -zv 142.68.18.1 20-80

 

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