Nmap is used primarily for port scanning. It is therefore important to differentiate between different types of port states available in Nmap. There are six possible port states recognized by Nmap:
- open – indicates that an application is listening for connections on the port. The primary goal of port scanning is to find these.
- closed – indicates that the probes were received but but there is no application listening on the port.
- filtered – indicates that the probes were not received and the state could not be established.
- unfiltered – indicates that the probes were received but a state could not be established. In other words, a port is accessible, but Nmap is unable to determine whether it is open or closed.
- open/filtered– indicates that the port was filtered or open but Nmap couldn’t establish the state.
- closed/filtered – indicates that Nmap is unable to determine whether a port is closed or filtered.