Port 1021 — Reserved for Experiments

What This Port Actually Is

Port 1021 is not empty or abandoned. It has a job: it exists to be used by experiments.¹

It's part of the well-known ports range (0-1023), officially reserved for temporary, experimental use according to RFC3692. If you see traffic on port 1021, it's most likely a researcher or engineer testing a new protocol idea—not a permanent service.

Why This Matters

The Internet doesn't let you just pick random port numbers for testing. If you do, you risk colliding with actual services, confusing systems, breaking production deployments. Port 1021 (and a handful of similar numbers) exist as sandboxes. They say: "Try your idea here. It's safe. We know this is temporary."

This is how protocol innovation happens quietly: RFC authors, researchers, and engineers use ports like 1021 to prototype ideas. Most of those experiments fail or get folded into other standards. Some become the backbone of the modern Internet. The port itself remains unchanged either way—still available for the next person with an untested idea.

You Won't Find a Service Here

If you check your system with netstat or lsof, you probably won't find port 1021 listening. That's the point. It's reserved, not actively used, waiting for someone who needs it.

On systems that do use it, you might see old references to Mac OS X NetInfo services (which have since moved on)—but those are artifacts, not the port's true purpose.²

How to Check What's Listening

If you want to see if anything is using port 1021 on your system:

Linux/macOS:

lsof -i :1021
netstat -tuln | grep 1021
ss -tuln | grep 1021

Windows:

netstat -ano | findstr :1021

You'll almost certainly see nothing. That's correct. The port is doing its job: staying quiet until someone needs it.

The Bigger Picture

Port 1021 is one of a small set of RFC3692-style experimental ports reserved across TCP, UDP, SCTP, and DCCP.¹ These ports let the Internet evolve without accidents. Someone can test a new DNS extension, a novel routing protocol, or an experimental congestion control algorithm—and the whole system keeps working because the experimental traffic is isolated to known, reserved space.

It's engineering humility: the admission that not every idea is ready for production, and that's not just okay—it's essential.