Port 1443 lives a double life. IANA says it belongs to one thing. The Internet uses it for something else entirely.
What IANA says
Port 1443 is officially registered to ies-lm—the Integrated Engineering Software License Manager.1 This is a license checkout service for IES's electromagnetic simulation tools. If you've never heard of it, you're not alone. Almost nobody uses this.
What actually runs here
In practice, port 1443 is commonly used for Microsoft SQL Server.2 Specifically, it's where SQL Server ends up when an administrator decides to move it from the default port 1433.
Why change one digit? The theory is "security through obscurity"—if attackers are scanning for SQL Server on 1433, maybe they won't find it on 1443.
The reality: anyone scanning for SQL Server is scanning the entire port range. Changing 1433 to 1443 is like hiding your house key under a rock next to the doormat instead of under the doormat itself. You feel clever. You are not safer.
The registered port range
Port 1443 falls in the registered port range (1024–49151). These ports are registered with IANA for specific services, but the registration is more suggestion than enforcement. Nothing stops you from running whatever you want on these ports.
This is why the official assignment (license manager) and actual usage (SQL Server) can be completely different. IANA maintains the list. The Internet does what it wants.
Why this matters
Using port 1443 for SQL Server creates two problems:
Port conflict potential: If you actually need to run the IES license manager (unlikely but possible), you now have a collision. Two services can't both listen on the same port.3
False sense of security: Moving SQL Server to 1443 doesn't hide it. Attackers who scan for SQL Server will find it. The only thing that changes is your documentation now has to explain why your SQL Server isn't on the standard port.
How to check what's listening
On Linux or macOS:
On Windows:
If you see SQL Server here instead of a license manager, you're seeing the common unofficial use.
The honest truth about unassigned and misused ports
The port number system only works if everyone agrees what the numbers mean. But agreement is optional. IANA assigns ports. Vendors register ports. Administrators ignore both and pick whatever seems convenient.
Port 1443 is a perfect example: officially assigned, rarely used as intended, commonly repurposed for something completely different. This is the Internet's version of using a screwdriver as a chisel. It works. It's not what the tool was designed for. Everyone does it anyway.
If you're running SQL Server on 1443: it works, but don't pretend it's a security measure. If you need security, use encryption, authentication, and firewall rules—not a different port number.4
Related ports
- Port 1433 — The actual default port for Microsoft SQL Server
- Port 443 — HTTPS, what people sometimes confuse this port with
- Port 3389 — Remote Desktop Protocol, another common Windows infrastructure port
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