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

We can easily list open ports in Linux on a local machine using the netstat or several other Linux commands such NMAP.

In this guide, we will show you how to determine if ports on a remote host are reachable/open using simple netcat (in short nc) command.

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.

# yum install nc [On CentOS/RHEL]
# dnf install nc [On Fedora 22+]
$ sudo apt-get install netcat [On Debian/Ubuntu]

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

$ nc -zv 22

In the command above, the flag:

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

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

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

$ nc -zv 20-80

For more examples and usage of netcat command, read through our articles as follows.

  1. Transfer Files Between Linux Servers Using netcat Command
  2. Linux Network Configuration and Troubleshooting Commands

That’s all. In this article, we explained how to check if ports on a remote host are reachable/open using simple netcat commands. Make use of the comment section below to write back to us concerning about this tip.

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