NMap

NMap is a free and open source network mapping tool that is available for Windows, Linux, and macOS. Network admins have appreciated the immense power that this free tool has. The tool works using raw IP packets that are sent throughout a network. This tool can do an inventory of the devices connected to a target network, identify the open ports that could be exploited, and monitor the uptime of hosts in the network.

This tool is also able to tell the services running on a network's hosts to fingerprint the operating systems used by the hosts and to identify the firewall rules being enforced in the network. NMap has a command-line interface, but there is a similar tool that has a graphical user interface called Zenmap. Zenmap is a tool for beginners that is simpler to use, and that comes with all the functionalities of NMap. The functionalities are, however, listed in menus, and thus, users do not have to remember commands, as is the case for NMap. Zenmap was created by the same developers of NMap just to serve the users that wished to have a GUI on their scanning tools for viewing results in a simplified way.

NMap works mainly through commands supplied by a user on a command-line interface. Users begin by scanning a system or network for vulnerabilities. A common way of doing this is by typing one of the following commands:

    #nmap www.targetsite.com
    #nmap 255.250.123.189  

For the preceding commands, the target site is the one you wish to have NMap scan. It works with either the site's URL or IP address. This basic command is mostly used in combination with other commands, such as TCP SYN Scan and Connect, UDP Scan, and FIN Scan. All of these have their equivalent command phrases. Figure 1 shows a screenshot of the NMap scanning two IP addresses. In the screenshot, the IP addresses being scanned are 205.217.153.62 and 192.168.12.3. Note how NMap shows the results for the scans, giving the open or closed ports and the services they allow to run: