Why can't NMAP scan the port
NMAP is a well-known network port scanning tool. But many newcomers find that using NMAP often fails to scan any ports, especially mobile phones and the like. There is actually a misunderstanding. Scanning ports is to discover open ports on hosts/devices for later use. In order to detect the port, the scanning tool will send a data packet to the target, and then judge the open status of the port according to the response packet. If the target does not respond, the scanning tool will not be able to detect port conditions.
Ordinary personal computers and mobile phones will open ports when transmitting network data. But at this time, the port is occupied. Once data is sent or received, the port is automatically closed. During this time period, even if the scanning tool happens to send packets to this port, no response packets will be received. Only services such as Web and file sharing will open the port for a long time. After the listening state is enabled, it will respond to the packets sent to the port. However, ordinary computers and mobile phones rarely open such services, so the port cannot be scanned.