# WHATPORT(6123)

## NAME

port 6123 — Apache Flink JobManager RPC (IANA: Backup Express) — Apache Flink's JobManager RPC port — registered to Backup Express, but Flink is what you find.

Protocol: TCP  
IANA registry

## DESCRIPTION

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.

## EXPOSURE

**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.

## CHECK

```sh
nc -vz TARGET 6123
```

## SEE ALSO

- docs — [Apache Flink — Configuration (jobmanager.rpc.port)](https://nightlies.apache.org/flink/flink-docs-stable/docs/deployment/config/) (nightlies.apache.org)
- source — [apache/flink on GitHub](https://github.com/apache/flink) (github.com)
- iana — [IANA Service Name and Transport Protocol Port Number Registry — 6123 (backup-express)](https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=6123) (iana.org)

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HTML: <https://whatport.net/6123/> · JSON: <https://whatport.net/6123.json> · full dataset: <https://whatport.net/ports.json>