Port 27015: Source engine
Port 27015 is the default game and server-browser query port for games built on Valve's Source engine, including Counter-Strike and Team Fortress 2. Dedicated servers use it for both gameplay traffic and for responding to server-list queries.
| Port number | 27015 |
|---|---|
| Service | Valve Source engine game/query port |
| Protocol | TCP/UDP |
| Category | Gaming |
| Default encryption | No |
How do I check whether port 27015 is open?
Port 27015 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 27015 | 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 27015 | 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 ':27015 ' | Lists the process bound to port 27015 on Linux. On macOS use lsof -nP -iTCP:27015 -sTCP:LISTEN, on Windows netstat -ano | findstr :27015 |
| Is it open on a remote host? | sudo nmap -sU -p 27015 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 ':27015 ' | Shows the UDP socket bound to port 27015. 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 27015 used for?
Port 27015 is the default game and server-browser query port for games built on Valve's Source engine, including Counter-Strike and Team Fortress 2. Dedicated servers use it for both gameplay traffic and for responding to server-list queries.
Is port 27015 TCP or UDP?
Port 27015 (Source engine) uses TCP/UDP.
Is port 27015 secure?
Port 27015 is not encrypted by default. Where possible, use an encrypted alternative or tunnel it over TLS or a VPN.
Should I open port 27015 on my firewall?
Only if you specifically need Source engine. Expose it to the smallest set of trusted sources, and never open database or Windows-service ports to the whole internet.