An IANA registration for a test-equipment control port, with no public documentation.
IANA registers 3889 as dandv-tester, "D and V Tester Control Port", to a private assignee. It is the control channel for a piece of vendor test equipment; no protocol specification or product documentation is publicly available under that name. The registration is all there is to report. If 3889 is open on something you own, identify it from the listening process, not the registry.
Do not expose
A control port for instrumentation, with no documented authentication — an interface that drives hardware should not be internet-reachable.
$ sudo lsof -nP -iTCP:3889 -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.