c# 获取对应ip的NTP时间

public static DateTime GetNetworkTime()
{
//default Windows time server
const string ntpServer = "1.cn.pool.ntp.org";

// NTP message size - 16 bytes of the digest (RFC 2030)
var ntpData = new byte[48];

//Setting the Leap Indicator, Version Number and Mode values
ntpData[0] = 0x1B; //LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)

var addresses = Dns.GetHostEntry(ntpServer).AddressList;

//The UDP port number assigned to NTP is 123
var ipEndPoint = new IPEndPoint(addresses[0], 123);
//NTP uses UDP
var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

socket.Connect(ipEndPoint);

//Stops code hang if NTP is blocked
socket.ReceiveTimeout = 3000;

socket.Send(ntpData);
socket.Receive(ntpData);
socket.Close();

//Offset to get to the "Transmit Timestamp" field (time at which the reply
//departed the server for the client, in 64-bit timestamp format."
const byte serverReplyTime = 40;

//Get the seconds part
ulong intPart = BitConverter.ToUInt32(ntpData, serverReplyTime);

//Get the seconds fraction
ulong fractPart = BitConverter.ToUInt32(ntpData, serverReplyTime + 4);

//Convert From big-endian to little-endian
intPart = SwapEndianness(intPart);
fractPart = SwapEndianness(fractPart);

var milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);

//**UTC** time
var networkDateTime = (new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc)).AddMilliseconds((long)milliseconds);

return networkDateTime.ToLocalTime();
}

// stackoverflow.com/a/3294698/162671
static uint SwapEndianness(ulong x)
{
return (uint)(((x & 0x000000ff) << 24) +
((x & 0x0000ff00) << 8) +
((x & 0x00ff0000) >> 8) +
((x & 0xff000000) >> 24));
}