No IANA registration and no notable service — an open 5877 is a local choice, not a protocol.
5877 is unassigned in the IANA registry and is not the documented default of any widely used server. The surrounding numbers are thinly allocated, which is exactly why gaps here get taken by internal tooling and vendor agents. The port number carries no information about the protocol, so read it off the process or the service banner.
Expose with care
Unidentified listener. Establish the owning process and its authentication before deciding it can be reachable.
$ sudo lsof -nP -iTCP:5877 -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.