# listen(on:backlog:loop:) Creates a listening server socket bound to a specific [`SocketAddress`](/documentation/Event/SocketAddress). ``` static func listen(on address: SocketAddress, backlog: Int32 = 128, loop: EventLoop = .shared) async throws -> ServerSocket ``` ## Parameters `address` The local endpoint to bind. Only IPv4 is currently supported — passing an IPv6 address will succeed at bind time only if the caller has previously coerced the kernel’s `AF_INET` socket to accept it (generally not recommended; IPv6 server support is a future enhancement). `backlog` The `listen(2)` backlog size. `loop` The event loop to drive. ## Return Value A [`ServerSocket`](/documentation/Event/ServerSocket) ready to accept connections. ## Discussion Applies `SO_REUSEADDR` before `bind(2)` so that restart-after-crash doesn’t block on `TIME_WAIT` sockets. On failure, closes the allocated fd before throwing, so no descriptor leaks (constitution Principle II). > Throws: ``doc://Event/documentation/Event/SocketError/socketCreationFailed(_:)``, > ``doc://Event/documentation/Event/SocketError/bindFailed(_:)``, or ``doc://Event/documentation/Event/SocketError/listenFailed(_:)``.