Port 790: Unassigned — A ghost in the well-known range

Port 790 is officially unassigned. No protocol owns it. No RFC defines it. IANA lists ports 788-799 as unassigned¹. But that doesn't mean this port is empty of history.

What Range This Port Belongs To

Port 790 sits in the well-known ports range (0-1023). These are the ports IANA carefully assigns to fundamental Internet services—HTTP on 443, DNS on 53, SSH on 22. They're supposed to be the stable foundation of the Internet's addressing system.

Being in this range without an assignment is unusual. It means IANA has reserved the space but never designated an official service for it. The port exists in a kind of limbo—important enough to be in the well-known range, but not important enough to have been claimed.

The Ghost of NetInfo

While port 790 has no official assignment, it does have a past.

For years, Mac OS X used ports in the 600-1023 range for RPC-based services, and port 790 was part of that ecosystem². It served NetInfo—Apple's hierarchical distributed database that stored administrative data for Mac servers. User accounts. Email configurations. Network filesystems. Printers. The kinds of things a server needs to know to function³.

Then Mac OS X 10.5 shipped in 2007, and NetInfo was gone. Completely removed. Replaced by Open Directory, which had been waiting in the wings since OS X 10.1⁴. And port 790 went silent.

No RFC was written. No formal deprecation was announced. The port just stopped being used.

Why Unassigned Ports Matter

The existence of unassigned ports like 790 reveals something about how the Internet's addressing system works.

Not every port needs to be assigned. IANA maintains the registry, but they can't predict every future protocol. Leaving ports unassigned creates space for experimentation, for proprietary systems, for services that serve a specific community without needing to be globally standardized.

Port 790's story—used unofficially by Apple, then abandoned—is actually common. Lots of ports have been used temporarily by companies or projects without formal IANA assignment. Some eventually get standardized. Others fade away when the software that used them disappears.

Checking What's Listening

Even though port 790 is unassigned, something could still be listening on it. Here's how to check:

On Linux or macOS:

sudo lsof -i :790
# or
sudo netstat -tulpn | grep :790

On Windows:

netstat -ano | findstr :790

If you find something listening on port 790, it's either:

1. Legacy Mac OS X software that hasn't been updated
2. Custom software using the port because it's unassigned
3. Malware trying to hide in an obscure port (less likely, but possible)

What This Port Teaches Us

Port 790 is a reminder that the Internet's infrastructure isn't just technical—it's also historical. Ports carry the ghosts of abandoned protocols. They mark where something used to be.

NetInfo served Mac servers for years. It held administrative data that kept networks running. Then Apple moved on, and the port that carried that data became just another unassigned number in the registry.

The port is still there, waiting. Officially unassigned. Technically available. But carrying the memory of what it used to be.