Registered to SynchroNet-db; rarely seen in the wild.
IANA lists 6100 TCP and UDP as synchronet-db, "SynchroNet-db", registered to Arne Haugland, and the same entry is copied into the /etc/services file on most Unix systems. There is no public protocol specification and no widely deployed open-source implementation, so a scanner labelling 6100 as "SynchroNet-db" is reading the registry, not fingerprinting the service. If you find it listening, identify the process on the host rather than trusting the name — this is a plausible port for an in-house or vendor application to squat on.
Expose with care
You cannot make a defensible call on a port whose actual occupant is unidentified; find the process, then decide. Treat an unknown listener on a public interface as something to close until it is explained.
$ sudo lsof -nP -iTCP:6100 -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.