Beginner's questions to NTP configurationoption "peer" - NTP

This is a discussion on Beginner's questions to NTP configurationoption "peer" - NTP ; Hello, I am quite new to questions regarding time synchronisation and hope this is the right place to post my questions. I am trying to configure time synchronisation via NTP in a small to medium size network. Reading through several ...

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Thread: Beginner's questions to NTP configurationoption "peer"

  1. Beginner's questions to NTP configurationoption "peer"

    Hello,
    I am quite new to questions regarding time synchronisation and hope this
    is the right place to post my questions. I am trying to configure time
    synchronisation via NTP in a small to medium size network. Reading
    through several web pages and parts of the book of Mr. Mills I still
    have some questions, which I will post after briefly describing a part
    of the network.
    The network has a Meinberg GPS 167 clock, which serves as source for all
    time synchronisation. Usage of public time servers is not possible,
    because the network is isolated.
    Of each blade enclosure, one blade uses the Meinberg clock as time
    server and is the timeserver for other blades in the enclosure it is
    located in. The stratum 2 blades then use each other as peers. In case
    of a failing clock, these servers pretend to be stratum 5 (via fudge).
    My questions are:
    1) in the described network setup: if the stratum 2 host of an enclosure
    1 fails to synchronize with it's stratum 1 source...
    before:

    |-------------|
    | Lantime V4 |
    | Stratum 1 |
    |-------------|
    |
    |
    V
    |-------------| |-------------|
    | Enclosure 1 |<--peer------>| Enclosure 2 |
    | Blade 1 | | Blade 1 |
    | Stratum 2 | | Stratum 2 |
    |-------------| |-------------|
    |
    |
    V
    |-------------|
    | Enclosure 1 |
    | Blade 2 |
    | Stratum 3 |
    |-------------|

    ---------------------------
    after:

    |-------------|
    | Lantime V4 |
    | Stratum 1 |
    |-------------|
    |
    X

    |-------------| |-------------|
    | Enclosure 1 |<--peer------>| Enclosure 2 |
    | Blade 1 | | Blade 1 |
    | Stratum ? | | Stratum 2 |
    |-------------| |-------------|
    | ___________/
    | /
    V /
    |-------------|
    | Enclosure 1 |
    | Blade 2 |
    | Stratum 3 |
    |-------------|

    In the documentation it is written that "Should one of the peers lose
    all reference sources or simply cease operation, the other peers will
    automatically reconfigure so that time and related values can flow from
    the surviving peers to all hosts in the subnet". Does the above
    ASCII-art describe this behaviour correctly?
    2) If a stratum 2 host has peer connections to other stratum 2 hosts AND
    it's network connection to the stratum 1 server(s) fail... Does the host
    in question
    a) drop to stratum 3 (because it's next time source is the stratum 2
    peer) like it would if both peer sides used each other as time server
    via the "server" keyword?
    b) drop to it`s fudged stratum level (stratum 5 in this case)?

    Regards,
    Stefan

  2. Re: Beginner's questions to NTP configuration option "peer"

    Nottorf, Stefan wrote:

    > synchronisation via NTP in a small to medium size network. Reading
    > through several web pages and parts of the book of Mr. Mills I still


    Being able to read the book probably disqualifies you as a beginner.

    > have some questions, which I will post after briefly describing a part
    > of the network.
    > located in. The stratum 2 blades then use each other as peers. In case
    > of a failing clock, these servers pretend to be stratum 5 (via fudge).


    This can be dangerous. You risk a mutual appreciation society in which
    they all confirm each other's idea of the wrong time, and as the local
    clock driver appears to have a rather low root distance, a single real
    clock doesn't have to differ much to be rejected.

    I believe orphan mode may avoid this. I think preferring the real time
    server may also do so.

    On other approach is to fudge each clock to a different value with steps
    of two between them.


    > |-------------|
    > | Lantime V4 |
    > | Stratum 1 |
    > |-------------|
    > |
    > X
    >
    > |-------------| |-------------|
    > | Enclosure 1 |<--peer------>| Enclosure 2 |
    > | Blade 1 | | Blade 1 |
    > | Stratum ? | | Stratum 2 |
    > |-------------| |-------------|
    > | ___________/
    > | /
    > V /
    > |-------------|
    > | Enclosure 1 |
    > | Blade 2 |
    > | Stratum 3 |
    > |-------------|


    This will only happen if both enclosure 1 and enclosure 2's blade 1's
    are specified as servers of enclosure 1 blade 2. In this case ? is 3.
    Note. If they are both servers, the no fault case may actually have
    enclosure 2 blade 1 as the official reference source, although both will
    be used to discipline the time.

    >
    > In the documentation it is written that "Should one of the peers lose
    > all reference sources or simply cease operation, the other peers will
    > automatically reconfigure so that time and related values can flow from
    > the surviving peers to all hosts in the subnet". Does the above
    > ASCII-art describe this behaviour correctly?


    Probably not, because it probably assumes that rearrangement can add
    links implied by transitive relationships, when all it can do is reverse
    peer relations and choose a new spanning sub-tree.

    > 2) If a stratum 2 host has peer connections to other stratum 2 hosts AND
    > it's network connection to the stratum 1 server(s) fail... Does the host
    > in question
    > a) drop to stratum 3 (because it's next time source is the stratum 2
    > peer) like it would if both peer sides used each other as time server
    > via the "server" keyword?


    Drop to stratum 3.

    > b) drop to it`s fudged stratum level (stratum 5 in this case)?


    Note that you will probably need multiple networks for you to be able to
    have a failure of connectivity from just one of the peers to the
    Meinberg without it also losing contact with the other peers and its
    clients.

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