Port 799 sits in the well-known ports range with an official assignment that most people have never heard of and an unofficial use that disappeared nearly two decades ago.
What Runs on Port 799
TCP port 799 is officially assigned to "Remotely Possible"—a remote control software from Avalan Technology that competed with pcANYWHERE in the Windows NT era of the 1990s.12 The software allowed a client system to connect with a host system to communicate, transfer files, or assume complete control of its operations.
UDP port 799 is officially unassigned by IANA.3
The Mac OS X Connection
Port 799 also falls within the range (600-1023) that Mac OS X used for RPC-based services, including NetInfo.45 NetInfo was Apple's hierarchical distributed database that tracked administrative data—user accounts, email configurations, network filesystems, printers, and other system resources.
NetInfo was completely removed from Mac OS X with version 10.5 (Leopard), replaced entirely by Open Directory.6 The port range remains, but the service that used it is gone.
What This Port Tells Us
Port 799 demonstrates something true about the well-known ports range: it's an archaeological record. These 1,024 port numbers were assigned in an era when the Internet was smaller, when individual companies could claim ports for proprietary software, when Apple could reserve ranges for internal protocols.
The well-known ports weren't just for standards like HTTP or SMTP. They were also for "Remotely Possible" and a dozen other programs you've never heard of—software that mattered intensely to someone in 1995 and has now vanished completely.
Current Status
Today, port 799 is largely unused. Remotely Possible has long since disappeared from the remote control software market. NetInfo is gone. The port sits in the registry with its official assignment, waiting for traffic that will probably never come.
If you find port 799 open on a modern system, it's worth investigating. Historical reports indicate this port has occasionally been exploited by malware,7 though that's true of many unused well-known ports—they're attractive targets precisely because they're not commonly monitored.
How to Check What's Listening
On most systems, you can check if anything is using port 799:
Linux/macOS:
Windows:
If something is listening on this port on a modern system, you should know what it is and why it's there.
Why Unassigned and Forgotten Ports Matter
The well-known ports range is finite—only 1,024 numbers. Every assignment matters, even the forgotten ones. Port 799 is technically still assigned on TCP, which means no new protocol can claim it without going through IANA to request the old assignment be released.
These ghost ports are a reminder that the Internet's addressing system was designed in a different era, with different assumptions about how scarce or abundant port numbers would be. We're living with the archaeological layers of those decisions.
Port 799 did its job. It carried remote control sessions for Windows NT administrators. It helped Mac OS X systems find their directory information. Now it's mostly silent—a number in a database, a line in an RFC, a door that nobody knocks on anymore.
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