Apache Flink's JobManager RPC port — registered to Backup Express, but Flink is what you find.
IANA assigns 6123 to backup-express, Catalogic Software's Backup Express. In practice the occupant today is Apache Flink: jobmanager.rpc.port defaults to 6123, and TaskManagers connect to the JobManager on it, so every standalone, YARN, and Kubernetes Flink deployment exposes it internally. It is an RPC channel, not a web UI — Flink's dashboard is 8081. Seeing 6123 on a scan almost always means a stream-processing cluster.
Do not expose
Flink ships with no authentication on its RPC endpoints, and submitting a job is arbitrary code execution on the cluster; keep 6123 inside the cluster network.
$ nc -vz TARGET 6123Seen 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.