Port 3290: CAPS Logistics Toolkit (and VATSIM's Voice Channel)

What This Port Is

Port 3290 sits in the registered port range (1024–49151). These ports are registered with the IANA (Internet Assigned Numbers Authority), which means any application can claim one by submitting a registration — and unlike well-known ports (0–1023), no special system privileges are required to use them.

IANA lists port 3290 as assigned to CAPS LOGISTICS TOOLKIT - LM (service name: caps-lm), registered to a Joseph Krebs on both TCP and UDP.¹ Beyond that entry, the software leaves almost no trace on the Internet — no documentation, no active product page, no community. It may have been a niche enterprise tool, an internal project that got a formal registration, or something that simply never shipped at scale.

This happens more often than you'd expect. The registered port range has thousands of entries for software that quietly disappeared, leaving behind only a name in the IANA spreadsheet.

What Actually Uses This Port

Port 3290 UDP is well-known to a specific community: VATSIM (Virtual Air Traffic Simulation Network), one of the world's largest online flight simulation networks, where real pilots and enthusiasts fly virtual routes with human air traffic controllers providing live guidance.

VRC (Virtual Radar Client) — the ATC controller software used on VATSIM — uses UDP port 3290 for voice communication. Controllers who want to transmit and receive voice through the network need this port open and forwarded through their router.² Without it, voice fails silently. With it, you can hear a controller in the Netherlands clear a simulated 737 for approach into Amsterdam while sitting in your living room.

This is the port's actual life: a UDP voice channel for a global community of aviation enthusiasts roleplaying the world's air traffic system.

Why the Mismatch Exists

Nothing stops a developer from using any port they want. IANA registration is not enforcement — it's a coordination mechanism. If CAPS Logistics Toolkit registered port 3290 but never built significant adoption, and VATSIM's developers chose 3290 for VRC voice (possibly before checking the registry, possibly not caring), both can coexist as long as they don't need the same machine at the same time.

On most home networks, this never causes a conflict. The logistics software isn't running, and the flight simulation software is.

Checking What's Using This Port

To see if anything is currently bound to port 3290 on your machine:

macOS / Linux:

# Show what's listening on port 3290
lsof -i :3290

# Or with netstat
netstat -an | grep 3290

Windows (PowerShell):

netstat -ano | findstr :3290

With the process identified, cross-reference the PID against Task Manager (Windows) or ps aux (macOS/Linux) to see which application owns it.

If you're troubleshooting VATSIM voice issues specifically, the answer is almost always that UDP 3290 is blocked at your router or firewall. Forward the port to your machine and voice will typically start working.

What the Registered Range Means

The registered port range (1024–49151) is where applications live. Your database, your web server, your chat client — they all live here. IANA coordinates registrations to reduce conflicts between well-meaning developers, but coordination is voluntary. The range contains roughly 48,000 ports, thousands of registrations, and a long tail of entries for software that no longer exists, was never widely deployed, or has been quietly repurposed by someone else.

Port 3290 is a small illustration of how port registration works in practice: a name on paper, a different reality on the wire.