No IANA assignment and no established occupant — an application-chosen high port.
There is no IANA service registration for 9917 on TCP or UDP. Nmap records it as unknown, seen rarely enough that no pattern emerges. Nothing standard, nothing vendor-default, nothing notable in published malware writeups. Find the owning process rather than reading meaning into the number.
Expose with care
An unidentified listener deserves scrutiny, not a default allow. Establish what it is, then decide.
$ sudo lsof -nP -iTCP:9917 -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.