Set-DatetimeFromNtp

Set-DatetimeFromNtp.ps1

$Server = $args[0]
$StartOfEpoch=New-Object DateTime(1900,1,1,0,0,0,[DateTimeKind]::Utc)

[Byte[]]$NtpData = ,0 * 48
$NtpData[0] = 0x1B    # NTP Request header in first byte

$Socket = New-Object Net.Sockets.Socket([Net.Sockets.AddressFamily]::InterNetwork,
                                        [Net.Sockets.SocketType]::Dgram,
                                        [Net.Sockets.ProtocolType]::Udp)
$Socket.Connect($Server,123)
$t1 = Get-Date    # Start of transaction... the clock is ticking...
[Void]$Socket.Send($NtpData)
[Void]$Socket.Receive($NtpData)
$t4 = Get-Date    # End of transaction time
$Socket.Close()

$IntPart = [BitConverter]::ToUInt32($NtpData[43..40],0)   # t3
$FracPart = [BitConverter]::ToUInt32($NtpData[47..44],0)
$t3ms = $IntPart * 1000 + ($FracPart * 1000 / 0x100000000)

$IntPart = [BitConverter]::ToUInt32($NtpData[35..32],0)   # t2
$FracPart = [BitConverter]::ToUInt32($NtpData[39..36],0)
$t2ms = $IntPart * 1000 + ($FracPart * 1000 / 0x100000000)

$t1ms = ([TimeZoneInfo]::ConvertTimeToUtc($t1) - $StartOfEpoch).TotalMilliseconds
$t4ms = ([TimeZoneInfo]::ConvertTimeToUtc($t4) - $StartOfEpoch).TotalMilliseconds
 
$Offset = (($t2ms - $t1ms) + ($t3ms-$t4ms))/2

$datetime = ($StartOfEpoch.AddMilliseconds($t4ms + $Offset).ToLocalTime()).GetDateTimeFormats()[44]

Set-Date $datetime