Port 3545: CAMAC Equipment — A Physics Relic and a Tunneling Footnote

What Port 3545 Is

Port 3545 sits in the registered port range (1024–49151). These ports are assigned by IANA to specific services, but unlike well-known ports (0–1023), they don't require elevated privileges to use and their assignments carry less weight — software is free to use any unoccupied port, regardless of what IANA has written down.

IANA's official record: port 3545 belongs to CAMAC equipment, registered in July 2002, for both TCP and UDP. ¹

What CAMAC Is

CAMAC stands for Computer Automated Measurement and Control. It's a modular instrumentation standard developed in the late 1960s for nuclear physics experiments — think data acquisition from particle detectors, radiation monitors, and laboratory control systems. ²

CAMAC predates TCP/IP as a practical concern. Its registration in 2002 was largely a formality, documenting existing practice rather than defining new network software. If you're not running physics lab equipment, you won't encounter this use.

The Teredo Connection

Port 3545 has a second, unrelated life. Teredo — Microsoft's protocol for tunneling IPv6 traffic through IPv4 NAT gateways — occasionally uses port 3545 for relay server traffic after the initial handshake. ³

Teredo's primary server port is 3544. But relay servers, which handle the actual ongoing data transfer once the connection is established, can operate on different ports. Security researchers analyzing Teredo traffic have documented port 3545 appearing as a relay destination in packet captures.

If you see UDP traffic on port 3545 on a Windows machine, Teredo is a reasonable suspect — especially on systems running IPv6 applications behind NAT.

What the Registered Range Means

When you see a port in the 1024–49151 range, it could be:

• An officially registered service (like CAMAC here)
• Common unofficial software using a port out of convention
• Ephemeral traffic — your OS may assign high-numbered ports temporarily for outgoing connections
• Something unknown running locally that chose this port

Registered ports are a best-effort system. IANA maintains the list, but enforcement is zero.

How to Check What's Using Port 3545

On Linux or macOS:

# Show what's listening on port 3545
ss -tlnp | grep 3545
# or
lsof -i :3545

On Windows:

# Show active connections on port 3545
netstat -ano | findstr :3545
# Then look up the PID in Task Manager, or:
Get-Process -Id (Get-NetTCPConnection -LocalPort 3545).OwningProcess

If nothing is returned, nothing is listening. That's the expected result on most systems.