Ntp Client

Fri Feb 20 00:38:30 UTC 2004

Bruce McDonald wrote:
> Hello Rick
> 
> On 19-Feb-04, you wrote:
> 
> 
>>Bruce McDonald wrote:
>>
>>>Hello Rick
>>>
>>>On 19-Feb-04, you wrote:
>>>
>>>
>>>
>>>>Bruce McDonald wrote:
>>>>
>>>>
>>>>>Hello,
>>>
>>>
>>>>>I appologise for the long post.
>>>
>>>
>>>>>I have just spent a "fun" day yesterday trying to get ntpd to sync my
>>>>>clock to a
>>>>>timeserver, and have failed.
>>>
>>>
>>>>>The only time it did work was when I started X, went to Main Menu
>>>>>Button => System Settings => Date & Time and specified a timeserver
>>>>>there. Unfortunatly that only lets you use one server, I wanted to have
>>>>>several to keep my clock honest.
>>>
>>>
>>>>>A note to those who will suggest ntpdate and a cron job..... I really
>>>>>want to use ntpd as my clock gains ~20 seconds a day (rough estimate).
>>>
>>>
>>>>>I was unable to find any documentation that told me what to do
>>>>>properly. I think I figured out what to do with the ntp.conf file, but
>>>>>I don't see any traffic when I run tcpdump port ntp. Ntpq -p show my
>>>>>timeservers but none are marked.
>>>
>>>
>>>>>Ntpq -p:
>>>>>   remote refid st t when poll reach delay offset jitter
>>>>>
> 
> 
> ==============================================================================
> 
> 
>>>>>tick.usnogps.na 0.0.0.0         16 u    -   64    0    0.000    0.000
>>>>>4000.00
>>>>>timekeeper.isi. 0.0.0.0         16 u    -   64    0    0.000    0.000
>>>>>4000.00
>>>>>clock.redhat.co 0.0.0.0         16 u    -   64    0    0.000    0.000
>>>>>4000.00
>>>>>clock2.redhat.c 0.0.0.0         16 u    -   64    0    0.000    0.000
>>>>>4000.00
>>>
>>>
>>>>>This is what I have in my ntp.conf file:
>>>>>(Is there anything wrong here?)
>>>
>>>
>>>>># Prohibit general access to this service.
>>>>>restrict default ignore
>>>
>>>
>>>>># Permit all access over the loopback interface.  This could
>>>>># be tightened as well, but to do so would effect some of
>>>>># the administrative functions.
>>>>>restrict 127.0.0.1 
>>>
>>>
>>>
>>>>># -- CLIENT NETWORK -------
>>>>># Permit systems on this network to synchronize with this
>>>>># time service.  Do not permit those systems to modify the
>>>>># configuration of this service.  Also, do not use those
>>>>># systems as peers for synchronization.
>>>>># restrict 192.168.1.0 mask 255.255.255.0 notrust nomodify notrap
>>>
>>>
>>>
>>>>># --- OUR TIMESERVERS ----- 
>>>>># or remove the default restrict line 
>>>>># Permit time synchronization with our time source, but do not
>>>>># permit the source to query or modify the service on this system.
>>>
>>>
>>>>># restrict mytrustedtimeserverip mask 255.255.255.255 nomodify notrap
>>>>>noquery
>>>>># server mytrustedtimeserverip
>>>
>>>
>>>
>>>
>>>>># --- NTP MULTICASTCLIENT ---
>>>>>#multicastclient            # listen on default 224.0.1.1
>>>>># restrict 224.0.1.1 mask 255.255.255.255 notrust nomodify notrap
>>>>># restrict 192.168.1.0 mask 255.255.255.0 notrust nomodify notrap
>>>
>>>
>>>
>>>
>>>>># --- GENERAL CONFIGURATION --- #
>>>>># Undisciplined Local Clock. This is a fake driver intended for backup
>>>>># and when no outside source of synchronized time is available. The #
>>>>>default stratum is usually 3, but in this case we elect to use stratum
>>>>># 0. Since the server line does not have the prefer keyword, this
>>>>>driver # is never used for synchronization, unless no other other #
>>>>>synchronization source is available. In case the local host is #
>>>>>controlled by some external source, such as an external oscillator or #
>>>>>another protocol, the prefer keyword would cause the local host to #
>>>>>disregard all other synchronization sources, unless the kernel #
>>>>>modifications are in use and declare an unsynchronized condition. #
>>>>># server 127.127.1.0 # local clock server navobs1.usnogps.navy.mil
>>>>>server timekeeper.isi.edu server clock.redhat.com server
>>>>>clock2.redhat.com server ntp1.linuxmedialabs.com
>>>
>>>
>>>>>fudge   127.127.1.0 stratum 10
>>>
>>>
>>>
>>>>>#
>>>>># Log file (added Feb 18, 2004)
>>>>>#
>>>>>logconfig    all
>>>>>logfile        /var/log/xntpd
>>>
>>>
>>>>>#
>>>>># Drift file.  Put this in a directory which the daemon can write to.
>>>>># No symbolic links allowed, either, since the daemon updates the file
>>>>># by creating a temporary in the same directory and then rename()'ing
>>>>># it to the file.
>>>>>#
>>>>>driftfile /etc/ntp/drift
>>>>>broadcastdelay    0.008
>>>
>>>
>>>>>#
>>>>># Authentication delay. If you use, or plan to use someday, the #
>>>>>authentication facility you should make the programs in the auth_stuff
>>>>># directory and figure out what this number should be on your machine.
>>>>>#
>>>>>authenticate yes
>>>
>>>
>>>>>#
>>>>># Keys file.  If you want to diddle your server at run time, make a
>>>>># keys file (mode 600 for sure) and define the key number to be
>>>>># used for making requests.
>>>>>#
>>>>># PLEASE DO NOT USE THE DEFAULT VALUES HERE. Pick your own, or remote
>>>>># systems might be able to reset your clock at will. Note also that
>>>>># ntpd is started with a -A flag, disabling authentication, that
>>>>># will have to be removed as well.
>>>>>#
>>>>>keys        /etc/ntp/keys
>>>
>>>
>>>
>>>
>>>>>In case the firewall was blocking communication I added lines to allow
>>>>>ntp to pass.
>>>
>>>
>>>>>#Deny TCP and UDP packets to privileged ports
>>>>>$IPTABLES -A INPUT -i $EXTIF -p tcp --dport 123 -j ACCEPT
>>>>>$IPTABLES -A INPUT -i $EXTIF -p udp --dport 123 -j ACCEPT
>>>>>$IPTABLES -A INPUT -i $EXTIF -p udp --dport 0:1023 -j DROP
>>>>>$IPTABLES -A INPUT -i $EXTIF -p tcp --dport 0:1023 -j DROP
>>>
>>>
>>>>>Still no communication. Can anyone shed any light on how to get ntpd to
>>>>>work properly as a client?
>>>
>>>
>>>>Ah, um, are you on a cable or DSL router and is its firewall configured
>>>>to allow incoming TCP/UDP port 123?  I don't see anything evil in
>>>>your ntp.conf or iptables.
> 
> 
> 
>>>I am connected via a DSL modem with the linux box being the network
>>>router.
> 
> 
>>Ok, let's try something simple.  Try:
> 
> 
>>    tcpdump port 123
> 
> 
>>in one window, then stop and restart xntpd.  Verify that you actually
>>see traffic.  If not, you might try turning off iptables and trying
>>again.  If it works the second time, look higher up in your iptables
>>to see if you have a block before your "--dport 123 -j ACCEPT" lines.
> 
> 
> Due to the way PPPoE works with DSL, I needed to type tcpdump -i PPP0 port
> 123

Didn't realize you were on a DSL line, Bruce.  Sorry about that.

> Thanks Rick, you once again caused me to think in the right direction to
> find where a problem lies.
> 
> Now I can see traffic.  And the clock is correct, so I guess I will let it
> run and see if it drifts by a significant amount in the next couple of
> days.  Interestingly, the drift file says 0.00; I find that hard to
> believe.  I think I'll have to delete it and restart ntpd to recalculate
> the drift.

Ok, so what was the problem?  Inquiring minds want to know! :-)

> Thanks again.

"That's what we're here for!" (c) 2004, The Red Hat Install List ;-)
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- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-   Which is worse: ignorance or apathy?  I don't know.  Who cares?  -
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