The program nmap

This program allows to know remotely the TCP ports that are open on a machine. To do this, we use the switch "-p" followed by the port number that we want to scan. We then specify the IP address or DNS name of the target.

For example, to scan port 80 of an IP address 192.168.1.100 machine, we will use the following command:

nmap -p 80 192.168.1.100

If we want a scan of all ports, we can use the following command:

nmap -p- 192.168.1.100