Another undocumented pxc-* registration; in the wild the port is effectively free real estate.
IANA lists 4006 as pxc-spvr with no reference or contact, the same as its neighbours 4002 through 4007. No common daemon binds it by default, and scan frequency data puts it in the noise. Whatever answers here is an application that was configured onto the port, so identify it directly.
Expose with care
Judge the exposure of the service you actually find, not of the registry name.
$ nc -vz -w 3 TARGET 4006Seen 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.