CODEWITHSUNDEEP
vb.nettime
thehoten
thehoten

Reputation: 123

Difficulty connecting to an ntp time server

I am trying to use the following piece of code to connect to a time server and attain the time but have had no luck: 

Dim ntpServer As String = "time.windows.com"
Dim ntpData(47) As Byte
Dim addresses = Dns.GetHostEntry(ntpServer).AddressList
Dim EndP As IPEndPoint = New IPEndPoint(addresses(0), 123)

Dim soc As Socket = New Socket(AddressFamily.InterNetwork, _ 
      SocketType.Dgram, ProtocolType.Udp)

soc.Connect(EndP)
soc.Send(ntpData)
soc.Receive(ntpData)

soc.Close()

Tracing through the program I can't get past the following line of code soc.Receive(ntpData). What am I doing wrong?

Thanks

Upvotes: 3

Views: 1267

Answers (1)

Arno
Arno

Reputation: 5194

you need to provide some basic information to the server:

ntpData(0) = 27

ntpData(0) contains a section called firstByteBits.

This section needs to be set before sending the data to query for a reply.

First byte is 

 0 1 2 3 4 5 6 7 
+-+-+-+-+-+-+-+-+
|LI | VN  |Mode |
  • LI = leap indicator (0 in sent data)
  • VN = version number (3, bits 3 and 4 set)
  • Mode = Mode (client mode = 3, bits 6 and 7 set)

00011011 = 27 = 0x1B

And possibly a better NTP server. The time.windows.com:123 server pool is known to be slow, sometimes not responding for a while, and of low accuracy. Better: pool.ntp.org:123 (but please read what's written on poo.ntp.org about regular use).

e.g. RFC 5905 for more details.

Upvotes: 1

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