[ntp:hackers] Debugging help - quirk in 4.2.5p187

Hal Murray hmurray at megapathdsl.net
Sun Jul 12 07:06:01 UTC 2009


I've got 5 PCs handy. Glypnod is running old software.  It's got an old 
version of ntpd: 4.2.0b-rc1 at 1.1475-o.  It's got PPS and keeps reasonably good 
time.  I use it to monitor the others, but I don't rock that boat.

The others are all running the latest version of ntp-dev.  When Harlan sends 
out a message about a new snapshot, I grab the new bits and turn the crank.

Something changed with the last release.  I don't know where to look.  The 
symptom is that returned packets are getting dropped: reach is 0.

Can anybody give me some hints on how to debug this?  Are there counters 
somplace that will tell me why a packet gets dropped?


ntpq -p mini-mon
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*glypnod         .PPS.            1 u   16  256  377    0.195   -3.053   0.307
 shuksan         192.168.1.3      2 u  207  256  377    0.000    0.000   0.000
+xo-b3           64.246.18.59     3 u  253  256  377    1.603    2.137   0.491
 xo-c2           198.186.191.229  3 u   59  256    0    0.000    0.000   0.000
 GPS_PALISADE(0) .GPS.            0 l    3   32  377    0.000  -41.735   0.005

server 192.168.1.3 iburst maxpoll 8   # glypnod
server 192.168.1.5 iburst maxpoll 8   # shuksan
server xo-b3       iburst maxpoll 8
server xo-c2       iburst maxpoll 8
server 127.127.29.0 mode 2 noselect
fudge 127.127.29.0 flag2 1

b3 and c2 are almost identical systems.  They are running the same OS and the 
same binary of ntpd.  Their config files are identical, using the pool.

Note that shuksan has a non-zero reach, but the delay, offset, and jitter are 0.

Shuksan and mini-mon are both using Glypnod as sys-peer.

Shuksan has a similar view:
[murray at glypnod spam]$ ntpq -p shuksan
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*glypnod         .PPS.            1 u   47   64  377    0.239   -0.140   0.005
 mini-mon        192.168.1.3      2 u   84  256   57    0.000    0.000   0.000
 xo-b3           64.246.18.59     3 u   67  256   77    1.563    5.570   8.902
 xo-c2           198.186.191.229  3 u   81  256    0    0.000    0.000   0.000
[snip more noselect]

server glypnod iburst  maxpoll 8
server mini-mon    minpoll 8 maxpoll 8 noselect
server b3          minpoll 8 maxpoll 8 noselect
server c2          minpoll 8 maxpoll 8 noselect

Just in case, I commented out the restrict lines.  That didn't change anything.




tcpdump looks good to me.  I see pairs of packets.


Bad: mini-mon to shuksan
23:41:55.978950 IP (tos 0xc0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 76) mini-mon.ntp > shuksan.ntp: NTPv4, length 48
        Client, Leap indicator:  (0), Stratum 2, poll 8s, precision -20
        Root Delay: 0.000183, Root dispersion: 0.017822, Reference-ID: glypnod
          Reference Timestamp:  3456369249.979191024 (2009/07/11 23:34:09)
          Originator Timestamp: 0.031398085
          Receive Timestamp:    3456369446.979084011 (2009/07/11 23:37:26)
          Transmit Timestamp:   3456369715.978918075 (2009/07/11 23:41:55)
            Originator - Receive Timestamp:  -838597849.052314074
            Originator - Transmit Timestamp: -838597580.052480010
23:41:55.979100 IP (tos 0xc0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 76) shuksan.ntp > mini-mon.ntp: NTPv4, length 48
        Server, Leap indicator:  (0), Stratum 2, poll 8s, precision -22
        Root Delay: 0.000183, Root dispersion: 0.007537, Reference-ID: glypnod
          Reference Timestamp:  3456369380.045419761 (2009/07/11 23:36:20)
          Originator Timestamp: 3456369715.978918075 (2009/07/11 23:41:55)
          Receive Timestamp:    3456369715.975930716 (2009/07/11 23:41:55)
          Transmit Timestamp:   0.031400106
            Originator - Receive Timestamp:  -0.002987359
            Originator - Transmit Timestamp: +838597580.052482031

Bad: mini-mon to c2
23:42:19.978952 IP (tos 0xc0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 76) mini-mon.ntp > xo-c2.ntp: NTPv4, length 48
        Client, Leap indicator:  (0), Stratum 2, poll 8s, precision -20
        Root Delay: 0.000183, Root dispersion: 0.018173, Reference-ID: glypnod
          Reference Timestamp:  3456369249.979191024 (2009/07/11 23:34:09)
          Originator Timestamp: 0.000000000
          Receive Timestamp:    3456369677.980845834 (2009/07/11 23:41:17)
          Transmit Timestamp:   3456369739.978925425 (2009/07/11 23:42:19)
            Originator - Receive Timestamp:  3456369677.980845834 (2009/07/11 23:41:17)
            Originator - Transmit Timestamp: 3456369739.978925425 (2009/07/11 23:42:19)
23:42:19.982113 IP (tos 0xc0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 76) xo-c2.ntp > mini-mon.ntp: NTPv4, length 48
        Server, Leap indicator:  (0), Stratum 3, poll 8s, precision -19
        Root Delay: 0.024246, Root dispersion: 0.077011, Reference-ID: 198.186.191.229
          Reference Timestamp:  3456368618.604606808 (2009/07/11 23:23:38)
          Originator Timestamp: 3456369739.978925425 (2009/07/11 23:42:19)
          Receive Timestamp:    3456369739.973562395 (2009/07/11 23:42:19)
          Transmit Timestamp:   0.000000000
            Originator - Receive Timestamp:  -0.005363029
            Originator - Transmit Timestamp: +838597556.021074574

Good: mini-mon to b3
23:54:28.978964 IP (tos 0xc0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 76) mini-mon.ntp > xo-b3.ntp: NTPv4, length 48
        Client, Leap indicator:  (0), Stratum 2, poll 8s, precision -20
        Root Delay: 0.000183, Root dispersion: 0.029113, Reference-ID: glypnod
          Reference Timestamp:  3456369249.979191024 (2009/07/11 23:34:09)
          Originator Timestamp: 3456370199.982564572 (2009/07/11 23:49:59)
          Receive Timestamp:    3456370199.980899732 (2009/07/11 23:49:59)
          Transmit Timestamp:   3456370468.978933714 (2009/07/11 23:54:28)
            Originator - Receive Timestamp:  -0.001664840
            Originator - Transmit Timestamp: +268.996369141
23:54:28.980803 IP (tos 0xc0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 76) xo-b3.ntp > mini-mon.ntp: NTPv4, length 48
        Server, Leap indicator:  (0), Stratum 3, poll 8s, precision -19
        Root Delay: 0.115402, Root dispersion: 0.058105, Reference-ID: kyna.dalbaech.net
          Reference Timestamp:  3456369966.593515393 (2009/07/11 23:46:06)
          Originator Timestamp: 3456370468.978933714 (2009/07/11 23:54:28)
          Receive Timestamp:    3456370468.982382612 (2009/07/11 23:54:28)
          Transmit Timestamp:   3456370468.982620086 (2009/07/11 23:54:28)
            Originator - Receive Timestamp:  +0.003448897
            Originator - Transmit Timestamp: +0.003686371


-- 
These are my opinions, not necessarily my employer's.  I hate spam.





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