Commands to check if a port is open on our PC / Server or another remote

Sometimes we need to know if X port is open on a remote computer (or server), at that moment we have not a few options or tools to use:

Nmap

The first solution that many of us think is: Nmap , see article called: See open ports with NMap and measures to protect ourselves 

In case you do not want to do a whole scan, but simply want to know if a certain port is open on X computer / server, it would be like this:

nmap {IP_O_DOMINIO} -p {PUERTO} | grep -i tcp

Example:

nmap localhost -p 22 | grep -i tcp

O well:

nmap 127.0.0.1 -p 22 | grep -i tcp

What this does is simple, it asks the IP or Host if the given port is open or not, then grep filters and only shows the line they want to read, the one that tells them if it is open (open) or closed (closed) that port:

Well ... yes, nmap (Network exploration and port probing tool) works for us, but there are still other variants where you have to type less 🙂

nc

nc or netcat, it is a much simpler option to know if a port is open or not:

nc -zv {IP_O_DOMINIO} {PUERTO}

That is:

nc -zv 192.168.122.88 80

Here is a screenshot doing a test to a port that is open (80) and another to another port that is not (53):

El -zv what it does is simple, the v allows us to see if the port is open or not, while z closes the connection as soon as the port is checked, if we do not put the z then we would have to do a Ctrl + C to close the nc.

telnet

This is the variant that I used for a while (due to ignorance of the aforementioned), in turn telnet serves us much more than just knowing if a port is open or not.

telnet {IP_O_HOST} {PUERTO}

Here's an example:

telnet 192.168.122.88 80

The problem with telnet is closing the connection. In other words, on certain occasions we will not be able to close the telnet request and we will be forced to close that terminal, or otherwise in another terminal do a telnet killall or something similar. That is why I avoid using telnet unless I really need to.

The end!

Anyway, I hope this has been interesting for you, if someone knows any other way to know if a port is open or not on another computer, leave it in the comments.

regards