Port 291: Unassigned — A Reserved Space in the Well-Known Range

Port 291 belongs to the well-known port range (0-1023), the territory reserved for system services and protocols assigned by the Internet Assigned Numbers Authority (IANA). But port 291 has no assignment. It's part of a block (288-307) that IANA classifies as "Unassigned."¹

What Unassigned Means

When a port is unassigned, it doesn't mean it's broken or forbidden. It means IANA hasn't officially designated it for a specific protocol or service. The port exists—like every number from 0 to 65535—but no RFC claims it, no protocol owns it, and no standard service listens here by default.

Applications can still use port 291. Nothing stops a developer from binding a service to it. But without an official assignment, there's no guarantee what you'll find when you connect.

The Well-Known Range

Ports 0-1023 are called "well-known ports" or "system ports." They require elevated privileges to bind on Unix-like systems. This range is where the Internet's fundamental protocols live: SSH on 22, HTTP on 80, HTTPS on 443.

Port 291 sits among these giants but remains unclaimed. It's like an empty lot between skyscrapers—zoned for something important, but nothing was ever built.

Why Unassigned Ports Matter

The existence of unassigned ports in the well-known range serves several purposes:

Future Protocol Space: These ports provide room for future protocols that might need official assignments in the system range.

Private Use: Organizations can use unassigned ports for internal services without conflicting with standard protocols.

Breathing Room: Not every number needs to be claimed. Empty space prevents the namespace from becoming crowded and fragile.

The gap from 288-307 has been unassigned for decades. No urgent need has emerged to fill these twenty ports. That's not a failure of planning—it's evidence of restraint.

Checking Port 291

To see if anything is listening on port 291 on your system:

# On Linux/Mac
sudo lsof -i :291
netstat -an | grep 291

# On Windows
netstat -an | findstr :291

# Using nmap
nmap -p 291 localhost

If nothing responds, that's expected. Port 291 doesn't have a service waiting by default.

The Silence Between Services

In the well-known port range, silence is unusual. Ports 20, 21, 22, 23, 25, 53, 80, 110, 143, 443—every gap tells you something. Either a protocol died and left the space vacant, or no one ever needed it enough to claim it.

Port 291 falls into the latter category. For decades, the Internet has operated without needing to assign this number. Maybe it will stay empty forever. Maybe someday a new protocol will arrive that needs exactly this spot.

For now, it waits.