The Ceph monitor's v2 messenger port — cluster membership and the map every client needs.
IANA registers TCP 3300 to Ceph as the monitor port, and Ceph uses it for msgr2, the version 2 wire protocol introduced in Nautilus that adds encryption-in-transit and improved authentication; monitors bind both 3300 (v2) and the legacy 6789 (v1) so older clients still connect. Any client or daemon that wants to use the cluster starts by fetching the monmap and OSD map from a monitor here. Seeing 3300 means a Ceph cluster's control plane is reachable from wherever you scanned.
Do not expose
Monitors are the cluster's control plane, guarded only by cephx keys; keep the public Ceph network private and never route 3300 to the internet.
$ nc -vz TARGET 3300Seen 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.