Port 920 is officially unassigned by the Internet Assigned Numbers Authority (IANA). Despite sitting in the well-known ports range—the most controlled section of the port number space—this port has never received an official service assignment.
The Well-Known Range
Port 920 falls within the well-known ports (0-1023), also called System Ports. This range is reserved for the most fundamental Internet services and requires IETF Review or IESG Approval for official assignments.1
Unlike the registered ports (1024-49151) where anyone can request an assignment, or the dynamic ports (49152-65535) that are never assigned, well-known ports are tightly controlled. The fact that 920 remains unassigned after decades tells you something: either no service needed it badly enough to go through the formal process, or the IETF didn't consider proposed uses important enough to warrant assignment.
Unofficial Uses
Even without an official assignment, port 920 has been observed in the wild:
Mac OS X NetInfo (Legacy)
Port 920/TCP was used by NetInfo, Apple's directory services system in older versions of Mac OS X. NetInfo is long obsolete—replaced by Open Directory in Mac OS X 10.5—but systems with legacy configurations might still listen on this port.2
The SANS Internet Storm Center, which tracks attack activity across ports, shows minimal traffic on port 920, suggesting it's rarely exploited and rarely used.3
Checking What's Listening
To see if anything is listening on port 920 on your system:
On Linux/Mac:
On Windows:
If you see something listening and you don't know why, investigate. Unassigned ports being used can indicate either legacy software you forgot about or something you didn't intentionally install.
Why Unassigned Ports Matter
The existence of unassigned ports in the well-known range isn't a bug—it's a feature. Not every number from 0-1023 needs an official service. The gaps provide flexibility:
- Legacy systems can use them informally without conflicts
- Future critical services have room to grow if needed
- The IETF can be selective about what earns well-known status
Port 920 might remain unassigned forever. Or twenty years from now, a protocol so fundamental that it needs well-known status might claim it. For now, it's a quiet gap in a numbered system—officially empty, occasionally borrowed, always available.
Related Ports
- Port 111 — Portmapper/RPCbind, the official RPC port
- Port 1023 — The last well-known port (reserved)
- Port 1024 — The first registered port (marks the boundary)
Frequently Asked Questions
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