A Perforce server — p4d listens on 1666 by default, on a port registered to IBM NetView for AIX.
IANA registers 1666 as "netview-aix-6", part of the 1661-1670 block for IBM's NetView for AIX, but every real hit on this port is Perforce. The Helix Core server p4d listens for plaintext connections on 1666 by default, and every client — p4, P4V, the Git Fusion and build integrations — reads that default out of P4PORT. Perforce is heavily used in games and hardware/EDA shops, so 1666 usually marks a build farm or a studio's source-of-truth server. A server configured for TLS is addressed as ssl:host:1666 rather than moving ports.
Do not expose
A plaintext p4d exposes credentials and the entire depot history to anyone who reaches it; run it with SSL enabled and keep the port on a private network or behind a VPN, using a Helix Proxy or broker for remote sites.
$ p4 -p TARGET:1666 infoSeen 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.