1  class Program 2     { 3         static void Main(string[] args) 4         { 5             GetNetworkTime(); 6         } 7  8         public static DateTime GetNetworkTime() 9         {10             //default Windows time server11             const string ntpServer = "clock.via.net";12 13             // NTP message size - 16 bytes of the digest (RFC 2030)14             var ntpData = http://www.mamicode.com/new byte[48];15 16             //Setting the Leap Indicator, Version Number and Mode values17             ntpData[0] = 0x1B; //LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)18 19             var addresses = Dns.GetHostEntry(ntpServer).AddressList;20 21             //The UDP port number assigned to NTP is 12322             var ipEndPoint = new IPEndPoint(addresses[0], 123);23             //NTP uses UDP24             var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);25 26             socket.Connect(ipEndPoint);27 28             //Stops code hang if NTP is blocked29             socket.ReceiveTimeout = 3000;30 31             socket.Send(ntpData);32             socket.Receive(ntpData);33             socket.Close();34 35             //Offset to get to the "Transmit Timestamp" field (time at which the reply 36             //departed the server for the client, in 64-bit timestamp format."37             const byte serverReplyTime = 40;38 39             //Get the seconds part40             ulong intPart = BitConverter.ToUInt32(ntpData, serverReplyTime);41 42             //Get the seconds fraction43             ulong fractPart = BitConverter.ToUInt32(ntpData, serverReplyTime + 4);44 45             //Convert From big-endian to little-endian46             intPart = SwapEndianness(intPart);47             fractPart = SwapEndianness(fractPart);48 49             var milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);50 51             //**UTC** time52             var networkDateTime = (new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc)).AddMilliseconds((long)milliseconds);53 54             return networkDateTime.ToLocalTime();55         }56 57         // stackoverflow.com/a/3294698/16267158         static uint SwapEndianness(ulong x)59         {60             return (uint)(((x & 0x000000ff) << 24) +61                            ((x & 0x0000ff00) << 8) +62                            ((x & 0x00ff0000) >> 8) +63                            ((x & 0xff000000) >> 24));64         }65     }