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Thread: NTP Broadcast

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  1. #1

    NTP Broadcast


    I have recently installed NTP daemon (version 4.2.6p5) onto an embedded Linux module (Digi 9p9215) and although I have the ntp unicast server function running, I do not seem to be able to get the broadcast or manycast server functions working. I am syncying the local clock to GPS and using this as the ntp server. My ntp config file looks like:

    listen on *
    server 127.127.1.0 prefer minpoll 6 maxpoll 6
    fudge 127.127.1.0 stratum 0 refid GPS
    broadcast 192.168.15.255 minpoll 6 ttl 7
    manycastserver 192.168.15.255 minpoll 6 maxpoll 6

    I'm not sure if it is simply an error in the configuration file or if I need to do something else to enable broadcasting/multicasting.
    Any pointers would be VERY welcome. Thanks

  2. #2
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    Have you double checked the broadcast address? What is the network mask?

    The many cast address isn't in the multicast range. I think you should be using 224.1.1.1.

  3. #3
    Network mask is 255.255.240.0 and the IP of my server is 192.168.0.10 so I calculated a multicast address of 192.168.15.255 Also I tried a broadcast address of 255.255.255.255 without success.

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  5. #4
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    255.255.255.255 isn't a broadcast address. If the net mask is 255.255.255.255 then 0.0.0.0 is defined for the broadcast address, 192.168.15.255 looks right though. Maybe try 0.0.0.0 and see if it will work.

  6. #5
    Just tried 0.0.0.0 and unfortunately nothing. Not sure where to go from here. I assume if the broadcast is working it sends out a message to the broadcast address on regular intervals (minpoll?) and I thought the manycastserver responded to requests from the multicast address?

  7. #6
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    How are you testing?

  8. #7
    I'm using two separate ntp clients. One is very simple called SetTime, the other provides more information and is called Achron (provides info on LI, VN, Stratum, Poll, Precision etc.etc

  9. #8
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    One client listening to bcast and one to mcast? Both on the same network as the servers?

    Try packet sniffing to make sure you're debugging the right problem.

  10. #9
    Yes, I think that's my next move, although I have tried both clients with a different multicast server and they seem to pick up on 192.168.15.255. To make sure there were no conflicts, I unplugged the other server from the LAN to do these tests.

  11. #10
    -->
    Okay, so when looking with wireshark I am sending broadcasts to the specified address. Reconfiguring my client to receive broadcasts did the trick!
    Thanks for your input.

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