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Source Engine Server
Port 27015 is widely used by game servers running Valve's GoldSrc and Source engines. It allows multiplayer connection handling for popular games like Counter-Strike, Team Fortress, and Half-Life. The port facilitates client-server communications, server queries, and matchmaking. Although primarily associated with gaming, the port's openness can sometimes expose servers to attacks if not properly secured..
Port 27015 is commonly utilized for dedicated game servers built on Valve's GoldSrc and Source engine platforms. These engines support iconic titles including Counter-Strike, Team Fortress Classic, Half-Life, Left 4 Dead, Portal, and Garry's Mod. Server administrators configure this port to receive player connections, synchronize game data, and manage in-game events.
The port handles both gameplay data and out-of-band queries, such as retrieving server information, player lists, and server status. For matchmaking and updates, the engines implement protocols over this port—either UDP or sometimes TCP, depending on the server settings and specific game requirements. Most notably, Steam employs a master server query system leveraging this port for server listings.
Although traditionally the engine communicates over UDP, custom server setups may employ other transport protocols, but SCTP use is practically nonexistent here. The port remains unofficially standardized in the gaming community as the default connection point for Source and GoldSrc servers hosted on personal or rented infrastructure.