Status: Unassigned
Range: Well-Known Ports (0-1023)
Unofficial Use: Mac OS X NetInfo RPC services
The Gap Between Registry and Reality
Port 966 is officially unassigned according to IANA—the Internet Assigned Numbers Authority that maintains the official registry of port assignments.1 But if you looked at a Mac OS X system in the 2000s, you'd find port 966 in use.
This is the gap between what the registry says and what operating systems actually do.
What Actually Used Port 966
Apple's Mac OS X used ports 600-1023 for RPC-based services (Remote Procedure Call), and port 966 was among them. Specifically, it was used by NetInfo—a hierarchical distributed database that stored administrative data on Mac OS X Server.2
NetInfo tracked:
- User and group accounts
- Email configurations
- Network filesystem (NFS) settings
- Printer configurations
- Computer and resource information
This was before Mac OS X switched to using Open Directory and other modern directory services. NetInfo is largely obsolete now, but port 966 remains in the registry as unassigned—a fossil of a service that once existed.
What Well-Known Ports Are Supposed to Be
Port 966 sits in the well-known ports range (0-1023). This range was designed to be controlled. System services, fundamental protocols, things everyone needs—those get well-known ports. You need root privileges to bind to them on Unix-like systems.
The idea: reserve these ports for important, standardized services that need to be consistent across the Internet.
The reality: Operating system vendors used what they needed. Apple wanted RPC services on Mac OS X, so they used a range of well-known ports. The registry didn't always catch up.
How to Check What's Using Port 966
On Linux or macOS:
On Windows:
If you see something listening on port 966 today, it's either:
- A legacy Mac OS X system still running NetInfo
- Some other application that decided to use an unassigned port
- A custom service that picked a port number arbitrarily
Why Unassigned Ports Matter
The port registry isn't law. It's a map. When IANA says a port is unassigned, they mean "we haven't given this to anyone officially." They don't mean "nothing is using this."
Unassigned ports in the well-known range are useful for:
- Custom internal services that need predictable port numbers
- Legacy applications that predate formal IANA assignment
- Operating system vendors who need ports for proprietary services
But using an unassigned well-known port comes with risk. IANA could assign it tomorrow. Your custom service on port 966 could conflict with a future official assignment. That's why the registered ports range (1024-49151) exists—ports you can request officially for your application.
The Port That Was
Port 966 is a ghost. Officially unassigned, but historically used. A reminder that the Internet's infrastructure is built by people making practical decisions, not just following registries.
If you need a port for a custom service today, don't use 966. Use something in the dynamic/private range (49152-65535) or register something officially in the user ports range (1024-49151).
But if you're debugging a Mac OS X Server from 2005 and you see port 966 listening—now you know why.
Related Ports
- Ports 600-1023 — Range used by Mac OS X for RPC-based services
- Port 111 — Official RPC portmapper service
- Ports 49152-65535 — Dynamic/private ports for temporary or custom use
Frequently Asked Questions About Port 966
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