Port 1146: CAPIoverLAN — A ghost from the dial-up era

What This Port Is For

Port 1146 is officially registered with IANA for CAPIoverLAN—a protocol that allowed computers to access ISDN telephony hardware over a network.¹

CAPI (Common ISDN Application Programming Interface) was the standard way software talked to ISDN equipment. ISDN was digital telephone line technology from the 1990s—faster than analog modems but slower than modern broadband. CAPIoverLAN extended this so you could control ISDN hardware remotely instead of having it directly connected to your computer.²

The Registered Range

Port 1146 sits in the registered port range (1024-49151). These ports are registered with IANA for specific services, but unlike well-known ports (0-1023), they don't require special system privileges to use.

Anyone can request a registered port number for their protocol or service. IANA maintains the registry, but enforcement is largely based on convention—nothing technically prevents you from running something else on port 1146.

Why This Port Exists Today

ISDN is effectively dead. Broadband Internet, fiber optics, and mobile networks replaced it decades ago. Most modern networks have never seen ISDN traffic.

But port 1146 remains in the registry because port numbers, once assigned, are rarely removed. The registration is a historical marker—evidence that someone, somewhere, built a system that needed this.

Some legacy telecommunications systems might still use ISDN and CAPIoverLAN, particularly in industrial settings or regions where infrastructure upgrades happen slowly. But you're far more likely to see this port sitting unused than carrying actual traffic.

Check What's Listening

If you want to see whether anything is actually using port 1146 on your system:

Linux/Mac:

sudo lsof -i :1146
netstat -an | grep 1146

Windows:

netstat -ano | findstr :1146

If something appears, it's either a legacy ISDN system or—more likely—an application that chose this port number arbitrarily because it was available.

Why Unassigned and Obsolete Ports Matter

The port number system is a 65,535-slot catalog of Internet history. Ports like 1146 tell you what people were building in the 1990s. They show which technologies won and which disappeared. They're the archaeological record of networking.

Unassigned and obsolete ports also serve a practical function: they're available. When you need to run a custom service and don't want to conflict with anything standard, you pick a port from the registered or dynamic range that nothing else is using. Port 1146 is effectively available because ISDN is gone.

The registry preserves history but doesn't prevent reuse. That's by design.

Security Note

Because this port has no active modern use, if you see traffic on port 1146, investigate it. It's either legacy equipment you should know about, or something using an obscure port number to avoid detection.

Malware sometimes uses registered-but-unused ports precisely because they look official enough to escape casual notice. If you're not running ISDN hardware, port 1146 should be silent.

Related Ports

• Port 5031 — AVM CAPI-over-TCP, another ISDN-over-network protocol³
• Port 20000 — Usermin, which sometimes gets confused with telephony ports in scans