[ntp:questions] Question regarding broadcast client

Steve Kostecke kostecke at ntp.org
Mon Oct 20 21:28:40 UTC 2008

On 2008-10-20, John Zornig <j.zornig at uq.edu.au> wrote:

> On an isolated network, not connected to the internet, I have a  
> timeserver appliance connected to GPS which is doing NTP broadcast  
> across a UDP one way link to the client system I am trying to  
> configure as a broadcast client.

Good! You have a time source.

> On my client I have the following in the ntp.conf file. Note: novolley  
> is used as there is no return network path to the timeserver appliance.
> broadcastclient novolley
> disable auth

Since you are using 'novolley' ntpd has no way of calculating the
broadcast delay. The default broadcast delay is 4.0 ms (see
http://doc.ntp.org/4.2.2/confopt.html). If the delay across your UDP
link is different you may set it with the 'broadcastdelay' command.

ntpd needs to have a driftfile to store the frequency correction. On my
Debian system it is specified like this:

	driftfile /var/lib/ntp/ntp.drift

The directory should exist and be writeable by the ntp user.

> The clock on the client is within 2 minutes of the correct time. I run  
> ntpd and it does not set the time to match the timeserver.
> I run ntpd on the client with -D and I get regular messages coinciding  
> with the arrival of the udp packets.
> receive: at 1205<- mode 5 code 6 keyid 00000001 len  
> 48 mac 20 auth 2

That shows that the client is receiving the broadcast packets.

The broadcast server sends out NTP packets at 64 second intervals. So,
the maximum delay before the client sees the first broadcast packet is
64 seconds after startup. After ntpd receives the first broadcast packet
you will see a 1 in the "reach" column of the ntpq peers billboard
('ntpq -p'). Then, at 64 second intervals, you should see the reach
increase (e.g. 1, 3, 7, 11, 13, 17 ... assuming that it receives every
broadcast packet) until it reaches 377. The client ntpd should sync to
the server within 5 minutes. Once the client is synced to the server
you'll see an asterisk '*' to the left of the server name in the
client's ntpq peer billboard ('ntpq -p').

Please check the ntpq peer billboard on the client and paste it here if
you need further assistance.

> The client system is an uptodate Red Hat 5.2 system. The ntp.x86_64  
> version installed is 4.2.2p1-8.el5

FWIW The current stable release is 4.2.4p5.

Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/

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