netstat
A command that displays active connections, listening ports, and network statistics on a host.
The netstat command displays active TCP and UDP connections, listening ports, routing tables, and per-interface statistics on the local host. Network+ troubleshooting uses it to verify whether a service is bound to the expected port and to spot unexpected outbound connections that may signal malware. A key distinction: netstat shows connections from the host’s perspective—including TCP states like ESTABLISHED, TIME_WAIT, and LISTEN (UDP is connectionless and has no such states)—while nmap scans ports from the network. When a service fails to start, netstat -an reveals whether another process already occupies that port, which ping or tracert cannot.
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