Why does Nmap show closed ports

Question

I’ve been running Nmap scans, and I’ve noticed that some ports show as closed rather than filtered or open. Can someone explain what it means when Nmap shows a port as closed and why this would happen? Does it indicate that a service or firewall is actively blocking the port?

Answer 1

When Nmap reports a port as closed, it means that the target system is actively rejecting connections to that port. This typically occurs when no application is listening on the port, and the system responds with a TCP RST (Reset) packet to indicate that the connection attempt is not accepted.

• Closed Ports: Indicate that no service is listening on the port, and the system actively rejects connection attempts.

• Filtered Ports: Suggest that a firewall or filter is blocking the port, preventing Nmap from determining whether it's open or closed.

To conclude, a closed port means the system is actively rejecting connections, while a filtered port indicates that a firewall or filter is preventing Nmap from determining the port's status.