A port scan is an active scan in which the scanning tool sends various types of probes to the target IP address and then examines the responses to determine whether the service is actually listening.
| Nmap port status reported | Response from target | Nmap Analysis |
|---|---|---|
| Open | TCP SYN-ACK | The service is listening on the port |
| Closed | TCP RST | The service is not listening on the port |
| Filtered | No response from target or ICMP destination unreachable | The port is firewalled |