My task is to send a packet to 254.0.0.251 and get a response from another IP but to the same port from which it sent the request. This simple code works great in the simulator: import UIKit import Network class ViewController: UIViewController {     var  connection: NWConnection?     var  listener: NWListener?     let  host: NWEndpoint.Host = "224.0.0.251"     let  port: NWEndpoint.Port = 5353     var myport: NWEndpoint.Port = 0     let  params_out = NWParameters.udp     let  params_in = NWParameters.udp     override func viewDidLoad() {         super.viewDidLoad()         params_out.allowLocalEndpointReuse = true         params_in.allowLocalEndpointReuse = true         connection = NWConnection(host: host, port: port, using: params_out)         connection?.stateUpdateHandler = onStateDidChange(to:)         connection?.viabilityUpdateHandler = viabilityUpdateHandler(to:)         connection?.start(queue: .global())     }     func portForEndpoint(_ endpoint: NWEndpoint) -> NWEndpoint.Port? {         switch endpoint {         case .hostPort(_, let port):             return port         default:             return nil         }     }     func onStateDidChange(to state: NWConnection.State){         switch (state) {         case .preparing:             print("Connection state: preparing")         case .ready:             print("Connection state: ready")         case .setup:             print("Connection state: setup")         case .cancelled:             print("Connection state: cancelled")         case .waiting:             print("Connection state: waiting")         case .failed:             print("Connection state: failed")         default:             print("Connection an unknown state")         }     }     func viabilityUpdateHandler(to state: Bool){         if (state) {             NSLog("Connection is viable")             myport = portForEndpoint((connection?.currentPath?.localEndpoint)!)!             print(String(describing: myport))             server()         } else {             NSLog("Connection is not viable")         }     }     func server(){         do {             listener = try NWListener(using: params_in, on: myport)         } catch {             print("exception upon creating listener")         }         listener?.stateUpdateHandler = {(newState) in             print("server: \(newState)")             switch newState {             case .ready:                 print("listener ready")             default:                 break             }         }         listener?.newConnectionHandler = {(newConnection) in             newConnection.stateUpdateHandler = {newState in                 print("server1_: \(newState)")                 switch newState {                 case .ready:                     print("ready")                     self.receiveMessage(connection: newConnection)                 default:                     break                 }             }             print("Connection")             newConnection.start(queue: DispatchQueue(label: "newconn"))         }         listener?.start(queue: .global())     }     func receiveMessage(connection: NWConnection) {         connection.receiveMessage { (data, context, isComplete, error) in             if(data?.count ?? 0 > 0){                 print("Connection receiveMessage message: \(String(describing: data!.count))")             }             self.receiveMessage(connection: connection)         }     } } But on iPhone IOS 15.4.1, the error is: [] nw_path_evaluator_evaluate NECP_CLIENT_ACTION_ADD error [48: Address already in use] What did I do wrong or not do? Thanks for any help! Alex