[ntp:questions] Re: Can't get Windows/2000 Client to synchronize with my NTP server on CentOS 4.2

Richard B. Gilbert rgilbert88 at comcast.net
Sat Jan 14 02:36:45 UTC 2006

Mark Hansen wrote:

> I'm running Centos 4.2 a machine which acts as my 'network host', in 
> that it
> connects my internal home network to the Internet, provides a firewall 
> (via
> iptables), and other basic services, like NTP. I'm running ntp version 
> 4.2.0.a
> I was running RedHat 7.3 before this installation, and all was working 
> fine.
> I have tested this without the firewall, to make sure the firewall was 
> not
> the problem. The firewall should not restrict access to/from the 
> network host
> machine and the in-house network.
> I have NTP configured to synchronize against three servers, a Statum 2 
> server
> owned by a friend of mine, and two other public NTP servers.
> When I run ntpq -p, I can see that my server is properly synchronizing 
> against
> these other servers (also, I can see by looking at syslog that things 
> appear to
> be working).
> However, when synchronization software on my Windows/2000 workstation 
> attempts
> to synchronize with my NTP server, it doesn't get a response.
> I ran tcpdump on the CentOS machine and watched the NTP UDP port, and 
> saw the
> request come in, but nothing was sent back. On the Windows/2000 
> machine, I've
> run w32tm -test -v -once, and get back the following (this is just a 
> snippet,
> but I think it's the pertinent part):
>> BEGIN:NTPTry -- try
>>    BEGIN:ComputeInterval
>>    END  Line 2479
>>    Sending to server  48 bytes...
>>    NTP: didn't receive datagram
>>    Logging event 0x8000000B. 15 min until this event is allowed again.
>>    0x8000000B reported to System Log in Event Viewer
>> END  Line 1951
>> Time source failed to produce usable timestamp.
> When w32tm is making its attempts, I see the following messages
> in the syslog (when running ntpd with debugging turned on):
>> ntpd: input_handler: if=3 fd=7 length 48 from 0a0a9714
>> ntpd: receive: at 16<- restrict 184
>> ntpd: receive: at 16<- mode 3 code 2
>> ntpd: addto_syslog: select(): nfound=-1, error: Interrupted system call
> ( is my CentOS server machine, running ntpd, and
> is my Windows/2000 client machine).
> In looking at the source for ntpd, I see that one of the bits represented
> by the "184" is Authentication Required, so I tried running ntpd with the
> -A flag, but this didn't help.
> I've tried two additional clients on the Windows/2000 machine, one of
> which allows me to select the protocol version to use, and I tried 4, 
> 3 and
> 2 - with the same result.
> I went through some debugging tips found after googling, but these all 
> were
> focused on getting the server to synchronize with its peers, and not 
> about
> problems connecting to the server from clients.
> I'll include, below, my configuration file, and would be grateful if 
> someone
> could either spot the problem, or give me a pointer to how I can debug 
> client
> connection problems.
> Thanks,
> server my-friends-ntp-server prefer
> server ntp1.Level3.net
> server ntp2.Level3.net
> driftfile /var/lib/ntp/drift
> broadcastdelay 0.008
> restrict my-friends-ntp-server-IP mask nomodify
> restrict ntp1-IP mask nomodify
> restrict ntp2-IP mask nomodify
> # This is my internal network:
> restrict mask nomodify notrust notrap
> # The local address are unrestricted:
> restrict
> restrict

I'd suggest either losing the "restrict mask 
nomodify notrust notrap" statement, or omitting the notrust, or adding a
"restrict mask"  assuming that that is the 
address of the failing client.   Alternatively you could set up some 
form of authentication between your server and your client.

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