Nmap port status resolution

The nmap port status resolution is open, on which the application receives TCP connection or UDP packets. The port closed by closed is also accessible to nmap. It receives and responds to nmap detection packets. But no application listens on it. Filtered Because packet filtering prevents the probe packet from arriving at the port, nmap cannot determine whether the port is open. Filter out firewall devices, routing rules, or software firewalls on the host. Unfiltered is not filtered, which means the port is accessible, but nmap cannot determine whether it is open or closed. Only ACK Scans used to map firewall rule sets classify ports to this status. Open | filtered: it cannot be determined whether the port is open or filtered. The open port does not respond. No response may also mean that the packet filter discards the detection packet or any response it causes. UDP, IP protocol, FIN, Null, and other scans will be caused.