Port 3363: NATI Vi Server — The Remote Control Wire for Virtual Instruments

What Runs on Port 3363

Port 3363 belongs to National Instruments (NI, formerly NATI). It is the default TCP and UDP port for VI Server, the remote-control interface built into LabVIEW — NI's graphical programming language for test, measurement, and industrial automation.

IANA formally registered this port to NI with the service name nati-vi-server.¹

What Is a VI?

In LabVIEW, every program is called a Virtual Instrument (VI). The name is deliberate: when NI released LabVIEW in 1986, the whole point was that your computer could replace the physical instruments sitting on a lab bench — the oscilloscope, the signal generator, the data logger. You'd build a VI that looked and behaved like the real thing, ran on your Mac, and connected to actual hardware through an interface card.

The "virtual" part meant the instrument lived in software. The "instrument" part meant it was still doing real measurement work.

What VI Server Does

VI Server extends that idea across a network. When VI Server is running and listening on port 3363, other machines can:

• Call VIs running on that machine as if they were local
• Open, run, and close VIs remotely
• Read and write controls and indicators on a VI's front panel
• Inspect and modify VI properties at runtime

A test engineer's workstation in one building can drive an instrument rack in another. A CI pipeline can invoke LabVIEW executables on a test target. A monitoring application can pull readings from a remote sensor system. Port 3363 is the wire between them.

Who Uses This

LabVIEW is pervasive in places most software engineers never see:

• Physics research labs (particle accelerators, optical benches)
• Aerospace test facilities
• Semiconductor manufacturing (where "test" means catching faults before a chip ships)
• Industrial process control

When you see a rack of computers connected to a wall of hardware in a lab, there's a reasonable chance LabVIEW is running on some of those machines, and a reasonable chance port 3363 is open.

Port Range

Port 3363 falls in the registered port range (1024–49151). These ports are not controlled by the OS the way well-known ports (0–1023) are — any process can bind them without elevated privileges. IANA maintains the registry to reduce collisions, but registration is voluntary and doesn't prevent other software from using the same port.²

Security Considerations

VI Server's default configuration may allow connections from any host. In environments where LabVIEW executables control physical hardware — motors, heaters, pressure systems — an open VI Server port is a meaningful attack surface. NI provides access control lists (ACLs) to restrict which machines and VIs are accessible remotely. If you see port 3363 open on a system, check whether those ACLs are configured.

How to Check What's Listening

# macOS / Linux
sudo lsof -i :3363

# Or with ss (Linux)
ss -tlnp | grep 3363

# Windows
netstat -ano | findstr :3363
# Then look up the PID:
tasklist | findstr <PID>

If you see LabVIEW or an NI executable holding port 3363, that's expected. If you see something else, you've found an application that chose this port on its own — which happens with registered ports, since nothing enforces exclusivity.