Port 3478: STUN/TURN
Port 3478 is STUN and TURN, the protocols that help two devices behind NAT establish a direct connection for real-time voice, video, or WebRTC data. When a direct connection cannot be made, a TURN server on this port relays the media instead.
| Port number | 3478 |
|---|---|
| Service | STUN/TURN (NAT traversal for WebRTC) |
| Protocol | TCP/UDP |
| Category | Proxy & tunneling |
| Default encryption | No |
How do I check whether port 3478 is open?
Port 3478 carries TCP, so a connection either completes its handshake or it does not, which makes the check definitive.
| Question | Command | What to know |
|---|---|---|
| Is it open on a remote host? | nc -vz example.com 3478 | A TCP handshake either completes or it does not, so netcat gives a definitive answer in one line. |
| Same check on Windows | Test-NetConnection example.com -Port 3478 | Built into PowerShell. TcpTestSucceeded in the output is the answer; telnet is not installed by default on modern Windows. |
| What is listening locally? | ss -tlnp | grep ':3478 ' | Lists the process bound to port 3478 on Linux. On macOS use lsof -nP -iTCP:3478 -sTCP:LISTEN, on Windows netstat -ano | findstr :3478 |
| Is it open on a remote host? | sudo nmap -sU -p 3478 example.com | UDP has no handshake, so there is nothing to complete. nmap infers the state from whether an ICMP port-unreachable comes back, needs root, and is slow and easy to misread. A silent port may be open, filtered, or simply not replying to a probe it does not recognise. |
| What is listening locally? | ss -ulnp | grep ':3478 ' | Shows the UDP socket bound to port 3478. This is the reliable way to answer the question, because you are asking the host itself rather than guessing from outside. |
Replace example.com with the host you are testing. A blocked port and a port with nothing listening on it look identical from the outside, so if a service should be running, check locally before blaming the firewall.
Frequently asked questions
What is port 3478 used for?
Port 3478 is STUN and TURN, the protocols that help two devices behind NAT establish a direct connection for real-time voice, video, or WebRTC data. When a direct connection cannot be made, a TURN server on this port relays the media instead.
Is port 3478 TCP or UDP?
Port 3478 (STUN/TURN) uses TCP/UDP.
Is port 3478 secure?
Port 3478 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 3478 on my firewall?
Only if you specifically need STUN/TURN. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.