Why can't NMAP scan the port?

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. There is actually a misunderstanding. The purpose of scanning the port is to find the open ports on the host / device for later use. In order to detect the port, the scanning tool sends a packet to the target and then determines whether the port is open according to the response packet. If the target does not respond, the scanning tool cannot detect the port situation.

Ordinary personal computers and mobile phones open ports when transmitting data over the network. At this point, however, the port is in the occupied state. Once the data is sent or accepted, the port is automatically closed. During this period of time, even if the scanning tool happens to send a packet to this port, it will not receive a response packet. Only services such as Web and file sharing will open the port for a long time, and only when the listening state is enabled will the packets sent to the port respond. Ordinary computers and mobile phones rarely turn on such services, so the port cannot be scanned.