Explain what open, closed, and filtered port results mean in a Network Mapper (Nmap) scan, and why a result should be interpreted cautiously.

### Why this is right The three states distinguish evidence of a listening service, evidence that no service is listening, and insufficient visibility because packets may be blocked or responses unavailable. They are interpretations of scan observations, not unconditional claims about a system. ### The concept A port is a numbered endpoint used by network services. An **open** port indicates a service appears to respond; a **closed** port indicates the host is reachable but no service appears to be listening; a **filtered** port means a filter or missing response prevents a clear conclusion. Results can differ with scan method and network conditions. Use them to guide authorized assessment, not as proof that a service is safe or vulnerable. ### What a good answer covers - Define open, closed, and filtered in terms of observed responses. - Explain that filtered means the state is not clearly observable. - Note that scan results depend on network conditions and vantage point. - Limit scanning to authorized targets and scope. ### Terms - **Nmap**: Network Mapper. A tool that probes hosts and services. - **Port**: A numbered network endpoint associated with a service or process. ### Remember A scan reports what its probes could observe, not every fact about the target.