`-Pn`, also known as `No Ping`, is a command line option in NMAP – a free and open-source network scanner utility for network discovery and security auditing.
This option is used when you want to skip the step of pinging the target system while performing a scan. Normally, NMAP would first ping the system to check if it is online. When the `-Pn` option is used, NMAP skips this initial step and assumes that the target is online.
The NMAP Man Page, a highly reliable and recognized source, explains: “This option determines if a host is protected by a firewall or if it is offline and avoids scanning it. By default, NMAP would ping a system before scanning it. The ping helps to prevent ‘wasting’ time scanning systems that are not up. `-Pn` (No Ping) tells NMAP to skip this step and assume the hosts are online.” (https://nmap.org/book/man.html)
However, this feature `-Pn` becomes significant under certain circumstances, such as when protective firewalls are in place. Some systems may block ICMP echo requests (the mechanism used for pinging), rendering the target system ‘invisible’. By using the `-Pn` option, this blockage is circumvented, enabling you to scan the system regardless of whether the target responds to ping probes or not. This option is particularly handy for penetration testers and cyber security experts aiming to perform security audits for RPC services, web servers, and etc., which may be running behind firewalls.
Let’s illustrate with an example. Suppose there is a remote system you want to scan, but its firewall settings are blocking ping requests. If you try to run NMAP without the `-Pn` option, NMAP will ping the system, fails to get a response, and assumes that the system is offline. To bypass this, you could run the following command:
`nmap -Pn
This will instruct NMAP to skip the ping phase and proceed with scanning the system as if it was online, providing pertinent information about open ports and services on the target device.
So, the `-Pn` option proves to be useful when a target system is blocking ICMP echo requests or when you simply know for certain that the target system is up and want to save some time by skipping the ping step.
A point to note is that misuse of tools such as NMAP for unauthorized network scanning or malicious activities can lead to severe penalties, so always ensure that you’ve got explicit permission to perform any network scanning.
Source:
NMAP Man Page: https://nmap.org/book/man.html
