No IANA assignment, no documented service — an unclaimed high port.
IANA has no registration for 9621 on TCP or UDP, and Nmap records it as unknown at a very low frequency. Nothing standard, no product default, and no well-documented malware claims it. A listener here is an application that picked an arbitrary free port, so the useful move is to find the owning process rather than look the number up.
Expose with care
Unknown service, unknown risk. Identify the process first; an unlabelled high port is frequently something that was never meant to leave localhost.
$ sudo lsof -nP -iTCP:9621 -sTCP:LISTENSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.