Port 793: Unassigned — A gap in the well-known range

Port 793 is officially unassigned.¹ It exists in IANA's registry as part of a block (788-799) that has no designated service, no protocol, no official purpose.

What This Means

The well-known port range (0-1023) is managed by the Internet Assigned Numbers Authority (IANA). These ports are supposed to be assigned to fundamental Internet services—the protocols and applications that form the infrastructure of networked computing.

Most well-known ports were claimed decades ago. Port 22 got SSH in 1995. Port 80 has carried HTTP since 1992. Port 443 became HTTPS in 2000. These numbers are spoken for, permanently associated with the services that use them.

Port 793 is different. It's a gap. Nobody ever requested it for an official service, and IANA never assigned it to one.

Why Gaps Exist

Not every number in the well-known range needs to be allocated. Some ports remain unassigned because:

• No service needed them — The protocols that required well-known ports got them, and the ones that didn't never needed a number in this range
• Applications moved to higher ports — Modern services often use registered ports (1024-49151) instead
• Standards evolved — Some proposed protocols never materialized, leaving their reserved numbers unused

The unassigned ports aren't failures. They're just unused real estate in a namespace that doesn't need to be completely filled.

Historical Context

Earlier references suggested port 793 might have been used for Mac OS X RPC-based services like NetInfo,² but this appears to be part of a range (600-1023) that Apple documentation mentioned generally for RPC services—not a specific assignment for port 793.

NetInfo itself was removed from macOS entirely with version 10.5, replaced by Open Directory. If port 793 was ever used informally for these services, that usage is long obsolete.

What Could Be Listening

Just because port 793 has no official assignment doesn't mean nothing uses it. Software can bind to any port. You might find:

• Custom applications — Developers sometimes use unassigned ports for internal tools
• Legacy software — Old applications that chose arbitrary ports before checking IANA's registry
• Nothing at all — Most likely, this port sits completely unused on your system

How to Check

To see if anything is listening on port 793:

Linux/macOS:

sudo lsof -i :793
sudo netstat -an | grep 793
ss -tulpn | grep 793

Windows:

netstat -ano | findstr :793

If you see output, something is using the port. If not, it's closed—which is what you'd expect for an unassigned port with no standard service.

Why Unassigned Ports Matter

These gaps serve a purpose. They provide:

• Future flexibility — If a critical new protocol needs a well-known port, there are still numbers available
• Testing and development — Developers can use unassigned ports without conflicting with standard services
• Proof of restraint — Not every number needs an assignment; the registry isn't a race to fill every slot

The Internet's port system works because most ports remain unused. The 65,535 available port numbers vastly exceed the number of protocols that actually need them. Port 793 is part of that intentional surplus.

The Well-Known Range

Port 793 sits in the well-known range (0-1023), which means:

• IANA controls it — Only IANA can officially assign ports in this range³
• Root access required — On Unix-like systems, binding to ports below 1024 requires elevated privileges
• Permanent assignments — Once allocated, well-known ports rarely change

If you're building a service and need a port, don't use 793 just because it's unassigned. Use the registered port range (1024-49151) or the dynamic range (49152-65535). The well-known range is reserved for protocols that need universal recognition.