Port 3316: Unassigned — The Empty Slot Next to MySQL

What This Port Is

Port 3316 sits in the registered port range (1024–49151), which means it falls under IANA's jurisdiction for formal assignment. IANA has not assigned it to any service. It is officially unoccupied.

That said, unoccupied doesn't mean unused.

Known Informal Uses

Alternate MySQL port. MySQL's canonical port is 3306. When developers need to run a second database instance on the same machine — say, MariaDB alongside MySQL, or a test database alongside production — 3316 is a common choice. It's exactly ten numbers away from 3306, which makes it easy to remember and easy to spot in a config file.¹

You'll see this pattern in forum threads and configuration guides: someone needs two MySQL-compatible databases on one host, assigns one to 3306 and the other to 3316, and moves on. No registration required.

AzimuthVMS. Port 3316 has also been documented as used by AzimuthVMS, a CCTV recording and video management platform, for its internal database communication.²

What the Registered Range Means

The registered range (1024–49151) is where applications go to claim a permanent address. The process requires submitting a request to IANA, demonstrating a legitimate protocol or service, and following the review process defined in RFC 6335.³

Most of the range remains unclaimed. IANA lists thousands of ports in this range as simply unassigned — available for formal registration, but never requested. Port 3316 is one of them.

This creates a practical reality: unassigned registered ports are frequently borrowed informally. Software authors pick them because they're above 1023 (no root required on Unix systems), below the ephemeral range, and not already taken by something well-known. They're the neutral territory of the port space.

How to Check What's Listening on Port 3316

macOS/Linux:

sudo lsof -i :3316

or

ss -tlnp | grep 3316

Windows:

netstat -ano | findstr :3316

Then match the PID from the output to a process name in Task Manager or with:

tasklist | findstr <PID>

If something is listening, the process name will tell you what claimed it.

Why Unassigned Ports Matter

The port system works because most software respects the registry. MySQL uses 3306 because that's where clients expect to find it. Web traffic goes to 443 because browsers know to look there.

Unassigned ports like 3316 are the exception — informal, undocumented, and invisible to anything that doesn't already know to look. That makes them useful for internal tooling and test environments, but it also means a port scanner finding traffic on 3316 has no reference point. It could be a legitimate secondary database, a misconfigured service, or something that shouldn't be there.

When you find unexpected traffic on an unassigned port, the process behind it is the only honest answer.