Simple ntp setup, but network issue - NTP

This is a discussion on Simple ntp setup, but network issue - NTP ; Greetings - I am still working (when I have spare time) on diagnosing my problem communicating with an ntp server. As people helpfully pointed out to me last week, from my ntpq results (see below) it appears that I have ...

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Thread: Simple ntp setup, but network issue

  1. Simple ntp setup, but network issue

    Greetings -

    I am still working (when I have spare time) on diagnosing my problem
    communicating with an ntp server. As people helpfully pointed out to me
    last week, from my ntpq results (see below) it appears that I have a network
    communication problem and I should do some type of network trace to see what
    is occurring.

    [root@Bison root]# ntpq -p
    remote refid st t when poll reach delay offset
    jitter
    ================================================== ============================
    rainforest.neor 0.0.0.0 16 u - 1024 0 0.000 0.000
    4000.00
    *LOCAL(0) LOCAL(0) 10 l 21 64 377 0.000 0.000
    0.008

    A partial listing of the tcpdump showing three pings and starting the ntp
    service is below. I don't know how to interpret all of this, but am
    assuming that the two lines I have marked indicate my problem. I am not
    sure exactly what this tells me or how to fix it, so I am hoping to get some
    experienced guidance from the list here. The address 192.168.112.10 is my
    dsl modem which serves as my network gateway, bison is my linux server.

    Partial output of tcpdump
    Sent 3 Pings to rainforest.neorack.com
    11:31:41.839155 bison > rainforest.neorack.com: icmp: echo request (DF)
    11:31:41.840913 jeff.1651 > bison.ssh: P 208:260(52) ack 221 win 65179 (DF)
    11:31:41.880647 bison.ssh > jeff.1651: . ack 260 win 8576 (DF) [tos 0x10]
    *** 11:31:42.150646 arp who-has 192.168.112.10 tell bison
    *** 11:31:42.150939 arp reply 192.168.112.10 is-at 0:15:5:4f:ec:6f
    11:31:42.850665 bison > rainforest.neorack.com: icmp: echo request (DF)
    11:31:43.163271 0.00:40:8c:55:57:34.4000 >
    0.ff:ff:ff:ff:ff:ff.452:ipx-sap-req 4
    11:31:43.850660 bison > rainforest.neorack.com: icmp: echo request (DF)
    11:31:44.162307 0.00:40:8c:55:57:34.4000 >
    0.ff:ff:ff:ff:ff:ff.452:ipx-sap-req 4
    11:31:45.162242 0.00:40:8c:55:57:34.4000 >
    0.ff:ff:ff:ff:ff:ff.452:ipx-sap-req 4

    Started ntp service
    11:32:02.030685 bison.ntp > rainforest.neorack.com.ntp: v4 client strat 0
    poll 4 prec -6 (DF)
    11:32:02.102846 jeff.1661 > bison.10000: . ack 9983 win 65497 (DF)
    11:32:03.030690 bison.ntp > rainforest.neorack.com.ntp: v4 client strat 0
    poll 4 prec -6 (DF)
    11:32:04.030667 bison.ntp > rainforest.neorack.com.ntp: v4 client strat 0
    poll 4 prec -6 (DF)
    11:32:05.030668 bison.ntp > rainforest.neorack.com.ntp: v4 client strat 0
    poll 4 prec -6 (DF)
    11:32:06.030670 bison.ntp > rainforest.neorack.com.ntp: v4 client strat 0
    poll 4 prec -6 (DF)
    11:32:07.030662 bison.ntp > rainforest.neorack.com.ntp: v4 client strat 0
    poll 4 prec -6 (DF)
    11:32:08.030670 bison.ntp > rainforest.neorack.com.ntp: v4 client strat 0
    poll 4 prec -6 (DF)
    11:32:09.030669 bison.ntp > rainforest.neorack.com.ntp: v4 client strat 0
    poll 4 prec -6 (DF)

    I don't know if I need to make a configuration change in my linux server or
    in my gateway dsl box (an ActionTec appliance from Qwest). Below is the
    routing table and the hosts file for my server, if that helps. I also have
    the option of setting up Static Routes or Port Forwarding on the software in
    the dsl appliance, but I don't know what needs to be changed or the most
    appropriate place to change the configuration if there are options. Advice
    on this issue would be most appreciated, especially if I can learn something
    new that prevents me from running into similar problems in the future. I am
    a novice linux administrator so please give me the basics with some
    explanation. Thanks.

    [jeffb@Bison jeffb]$ netstat -rn
    Kernel IP routing table
    Destination Gateway Genmask Flags MSS Window irtt
    Iface
    192.168.112.0 0.0.0.0 255.255.255.0 U 0 0 0
    eth0
    169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0
    eth0
    0.0.0.0 192.168.112.10 0.0.0.0 UG 0 0 0
    eth0

    /etc/hosts
    127.0.0.1 bison localhost.localdomain localhost
    192.168.112.1 bison
    192.168.112.105 jeff
    192.168.112.100 pamk


    Jeff Boyce
    www.meridianenv.com

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  2. Re: Simple ntp setup, but network issue

    Jeff Boyce wrote:

    > Greetings -
    >
    > I am still working (when I have spare time) on diagnosing my problem
    > communicating with an ntp server. As people helpfully pointed out to me
    > last week, from my ntpq results (see below) it appears that I have a
    > network communication problem and I should do some type of network trace
    > to see what is occurring.
    >
    > [root@Bison root]# ntpq -p
    > remote refid st t when poll reach delay offset
    > jitter
    > ================================================== ============================
    >
    > rainforest.neor 0.0.0.0 16 u - 1024 0 0.000 0.000
    > 4000.00
    > *LOCAL(0) LOCAL(0) 10 l 21 64 377 0.000 0.000
    > 0.008
    >
    > A partial listing of the tcpdump showing three pings and starting the
    > ntp service is below. I don't know how to interpret all of this, but am
    > assuming that the two lines I have marked indicate my problem. I am not
    > sure exactly what this tells me or how to fix it, so I am hoping to get
    > some experienced guidance from the list here. The address
    > 192.168.112.10 is my dsl modem which serves as my network gateway, bison
    > is my linux server.
    >
    > Partial output of tcpdump
    > Sent 3 Pings to rainforest.neorack.com
    > 11:31:41.839155 bison > rainforest.neorack.com: icmp: echo request (DF)
    > 11:31:41.840913 jeff.1651 > bison.ssh: P 208:260(52) ack 221 win 65179 (DF)
    > 11:31:41.880647 bison.ssh > jeff.1651: . ack 260 win 8576 (DF) [tos 0x10]
    > *** 11:31:42.150646 arp who-has 192.168.112.10 tell bison
    > *** 11:31:42.150939 arp reply 192.168.112.10 is-at 0:15:5:4f:ec:6f


    The above two lines do not appear to be a problem. ARP is Address
    Resolution Protocol. In English, "Which one of you guys is
    192.168.112.10?" and the reply "It's me; my MAC address is
    0:15:5:4f:ec:6f". Now, whoever asked the question knows where to send
    messages addressed to 192.168.112.10.
    > 11:31:42.850665 bison > rainforest.neorack.com: icmp: echo request (DF)
    > 11:31:43.163271 0.00:40:8c:55:57:34.4000 >
    > 0.ff:ff:ff:ff:ff:ff.452:ipx-sap-req 4
    > 11:31:43.850660 bison > rainforest.neorack.com: icmp: echo request (DF)
    > 11:31:44.162307 0.00:40:8c:55:57:34.4000 >
    > 0.ff:ff:ff:ff:ff:ff.452:ipx-sap-req 4
    > 11:31:45.162242 0.00:40:8c:55:57:34.4000 >
    > 0.ff:ff:ff:ff:ff:ff.452:ipx-sap-req 4
    >


    I don't see any indication that rainforest.neorack.com replied to your
    pings (ICMP Echo Request). Which says that either:
    a. The ping never reached rainforest, or
    b. The reply from rainforest never made it back.

    > Started ntp service
    > 11:32:02.030685 bison.ntp > rainforest.neorack.com.ntp: v4 client strat
    > 0 poll 4 prec -6 (DF)
    > 11:32:02.102846 jeff.1661 > bison.10000: . ack 9983 win 65497 (DF)
    > 11:32:03.030690 bison.ntp > rainforest.neorack.com.ntp: v4 client strat
    > 0 poll 4 prec -6 (DF)
    > 11:32:04.030667 bison.ntp > rainforest.neorack.com.ntp: v4 client strat
    > 0 poll 4 prec -6 (DF)
    > 11:32:05.030668 bison.ntp > rainforest.neorack.com.ntp: v4 client strat
    > 0 poll 4 prec -6 (DF)
    > 11:32:06.030670 bison.ntp > rainforest.neorack.com.ntp: v4 client strat
    > 0 poll 4 prec -6 (DF)
    > 11:32:07.030662 bison.ntp > rainforest.neorack.com.ntp: v4 client strat
    > 0 poll 4 prec -6 (DF)
    > 11:32:08.030670 bison.ntp > rainforest.neorack.com.ntp: v4 client strat
    > 0 poll 4 prec -6 (DF)
    > 11:32:09.030669 bison.ntp > rainforest.neorack.com.ntp: v4 client strat
    > 0 poll 4 prec -6 (DF)
    >
    > I don't know if I need to make a configuration change in my linux server
    > or in my gateway dsl box (an ActionTec appliance from Qwest). Below is
    > the routing table and the hosts file for my server, if that helps. I
    > also have the option of setting up Static Routes or Port Forwarding on
    > the software in the dsl appliance, but I don't know what needs to be
    > changed or the most appropriate place to change the configuration if
    > there are options. Advice on this issue would be most appreciated,
    > especially if I can learn something new that prevents me from running
    > into similar problems in the future. I am a novice linux administrator
    > so please give me the basics with some explanation. Thanks.


    I'd say you need to fix your gateway. I'm not familiar with it but
    normally such a box keeps your internal traffic off the phone line and
    passes stuff addressed to networks other than 192.168.112. It may also
    act as a firewall and block some addresses, ports, or protocols.
    Normally a firewall would not pass in anything that was not seen as a
    response to an outgoing message (stateful packet inspection). Such
    boxes are generally configurable; usually with a web interface. The
    better ones generally come with instructions. You may be able to find
    some documentation on the web if you didn't get any with the box.
    >



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