Different behavior between ntpd 4.2.0 and4.2.4? - NTP

This is a discussion on Different behavior between ntpd 4.2.0 and4.2.4? - NTP ; Hello I just upgraded som e machines from Mandriva 2006 to 2008 and thus ntpd from 4.2.0 to 4.2.4. Using the exact same ntp.conf file I get different behavior on the two versions, and the 4.2.4 version does not work ...

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Thread: Different behavior between ntpd 4.2.0 and4.2.4?

  1. Different behavior between ntpd 4.2.0 and4.2.4?

    Hello

    I just upgraded som e machines from Mandriva 2006 to 2008 and thus ntpd from 4.2.0 to 4.2.4. Using the exact same ntp.conf file I get different behavior on the two versions, and the 4.2.4 version does not work as expected. I also downloaded the 4.2.4p5 source from ntp.org and installed but got the same behavior.

    The ntp.conf is quite simple:
    server nanna prefer minpoll 4 maxpoll 6 iburst
    server 127.127.1.0 # local clock
    fudge 127.127.1.0 stratum 12
    driftfile /etc/ntp/drift
    multicastclient # listen on default 224.0.1.1
    broadcastdelay 0.008

    This is the procedure I do to get this behavior:
    LAN connections ok, and restart of ntpd. I let ntpd sync and see with ntpq -c peers that server nanna is in use. If I disconnect the lan connection to nanna eventually ntpq -c peers shows that local clock is being used. However, if I connect the lan to nanna again ntpq -c peers shows that nanna is never accepted as ntp server, and local clock is used no matter how long I wait.
    Doing the same with ntpd 4.2.0 automatically reinstates nanna as ntp server to use.

    I've set up two machines with the same ntp.conf but different ntpd versions and run these commands when disconnected and after connection has been established again:
    # ntpq -c peers
    # ntpq -c as
    # ntpq -c "rl "

    To not drown this mail I've put the output here: http://www.linuxtips.info/?p=32

    Any input to this matter would be highly appreciated.

    BTW: If this post comes as html, then please tell me and also how I can make Outlook Web Access behave...

    --
    Johnny Ljunggren
    Systems Engineer, Surveillance
    Park Air Systems AS

    Postal address:
    PO Box 145NO-3191 Horten, Norway

    Office address:
    Bromsveien 17
    NO-3183 Horten, Norway

    Tel: +47 23 18 02 00
    Direct: +47 928 89 436
    Fax: +47 23 12 37 10

    www.parkairsystems.com

  2. Re: Different behavior between ntpd 4.2.0 and 4.2.4?

    Johnny Ljunggren wrote:
    >
    > I just upgraded som e machines from Mandriva 2006 to 2008 and thus

    + ntpd from 4.2.0 to 4.2.4. Using the exact same ntp.conf file I get
    + different behavior on the two versions, and the 4.2.4 version does not
    + work as expected. I also downloaded the 4.2.4p5 source from ntp.org and
    + installed but got the same behavior.
    >


    > LAN connections ok, and restart of ntpd. I let ntpd sync and see with

    + ntpq -c peers that server nanna is in use. If I disconnect the lan
    + connection to nanna eventually ntpq -c peers shows that local clock is
    + being used. However, if I connect the lan to nanna again ntpq -c peers
    + shows that nanna is never accepted as ntp server, and local clock is
    + used no matter how long I wait.
    > Doing the same with ntpd 4.2.0 automatically reinstates nanna as ntp

    +

    Interesting. If there is such a difference, it might explain why we are
    getting more reports of machines locking onto local clocks.

    Some basic rules.

    Never configure a local clock on a pure client and only configure one on
    a server if you understand the tradeoffs. Even without it, the clock
    frequency will continue to be corrected during a server outage.

    If you configure a local clock, ensure that you have enough real servers
    configured to completely outvote it. That is your basic problem here.

    Also, I hope you own nanna, as using minpoll 4 on a public server is
    likely to result in a kiss of death. You may want to review the "Slow
    convergence" thread to see if your reason for overriding the poll limits
    possibly is similar to the one that Dave Mills considers to take the
    application outside the scope of NTP.



  3. Re: Different behavior between ntpd 4.2.0 and4.2.4?

    Thanks for the input

    >> LAN connections ok, and restart of ntpd. I let ntpd sync and see with

    >+ ntpq -c peers that server nanna is in use. If I disconnect the lan
    >+ connection to nanna eventually ntpq -c peers shows that local clock is
    >+ being used. However, if I connect the lan to nanna again ntpq -c peers
    >+ shows that nanna is never accepted as ntp server, and local clock is
    >+ used no matter how long I wait.
    >> Doing the same with ntpd 4.2.0 automatically reinstates nanna as ntp


    > Interesting. If there is such a difference, it might explain why we are
    > getting more reports of machines locking onto local clocks.


    > Never configure a local clock on a pure client and only configure one on
    > a server if you understand the tradeoffs. Even without it, the clock
    > frequency will continue to be corrected during a server outage.


    I tried to keep the first post brief, but I'll fill in some more data here. This machine is also a backup server for another machine on the network. A slightly strange redundant setup. A typical setup of ours is a small number of computers (say 10) where two of the machines work as clients to a hardware NTP server (GPS-based) that has been provided by us or to us. One has got the setup in the first post, with the local clock, and the second has gps time server and server one as servers to connect to. As I understand it server two would not sync to server one if connection to the gps ntp server is lost without local clock on server one?

    These computers are set up with dual everything so the reason is to have server one and server two always in sync, so if one of the servers is down the rest of the machines will still be in sync.

    > Also, I hope you own nanna, as using minpoll 4 on a public server is
    > likely to result in a kiss of death. You may want to review the "Slow
    > convergence" thread to see if your reason for overriding the poll limits
    > possibly is similar to the one that Dave Mills considers to take the
    > application outside the scope of NTP.


    It's ours so no problem there. I'm not sure why minpoll is there in the first place, since we don't really need it. I'll read the thread and do some tests without it.

  4. Re: Different behavior between ntpd 4.2.0 and 4.2.4?

    Johnny Ljunggren wrote:

    + connect to. As I understand it server two would not sync to server one
    + if connection to the gps ntp server is lost without local clock on
    + server one?

    It won't synch to it, but neither will it diverge rapidly from it.

    In this case you would probably be better off configuring the two
    internal servers in orphan mode, at the same stratum. I'm not sure
    whether that changes the position about the GPS source becoming a
    falseticker due to lack of supporting votes.

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