NMAP (Network Mapper) is a highly versatile, and open-source network scanning tool which is used to monitor and identify network vulnerabilities. It can also be deployed to check whether a host is online or not. This tool is widely used by system and network administrators, penetration testers, and network enthusiasts.
To verify if a host is online using NMAP, utilize the Ping Scan (also known as PING Sweep). Most often recognized by the -sn command, the Ping Scan enables users to sweep the target to acknowledge if the system is online and capable of communication.
Below is a step-by-step technique to use NMAP for determining if a host is online:
1. Installation: If you don’t have NMAP installed on your system, download it from the official NMAP website (https://nmap.org/download.html). Installation varies depending on your operating system. “nmap.org” offers comprehensive installation guidelines for various systems (https://nmap.org/book/install.html).
1. Running NMAP: Open your terminal/command prompt and simply type “nmap” to check if it is properly installed. It is recommended to run NMAP as an administrator or use sudo (on Linux or MacOS) to avoid any restrictions.
1. Ping Scan: To check if a host is online, use the Ping Scan command followed by the IP address or hostname. For instance, the command might look like this: `nmap -sn [IP address/host name]` . When this command is executed, it sends an ICMP request to the target host. If the host is online, it should respond and NMAP will display the host is up.
1. Reading the result: After the scan, NMAP will present the scan results. If the target host is online, it will show “Host is up.” Otherwise, it will show “Host is down” if it received no response from the host.
To illustrate a checking mechanism, when running the command: `nmap -sn 192.168.1.1`, the result could appear like this:
`Starting Nmap [version] at [time]`
`Nmap scan report for [IP Address / Hostname]`
`Host is up (0.00020s latency).`
`Nmap done: 1 IP address (1 host up) scanned in [time] seconds`
This result implies that the host is currently online. It should be noted, however, that results may vary due to different networks and possible security measures in place.
Make sure you have legal permission to scan any network or a host as it might be considered an illegal activity depending on your regional laws (https://nmap.org/book/legal-issues.html).
Sources:
- NMAP Project, Download the Free NMAP Security Scanner for Linux/MAC/UNIX or Windows, Retrieved from: https://nmap.org/download.html
- NMAP Project, Install Guide, Retrieved from https://nmap.org/book/install.html
- NMAP Project, Understanding Legal Issues, Retrieved from https://nmap.org/book/legal-issues.html
