[ntp:questions] negative estbdelay?

Dave Johnson djohnson at sw.starentnetworks.com
Sat Oct 20 20:21:42 UTC 2007


Just ran into a system that has a estbdelay of -2.6 seconds.  Needless
to say this is causing the system to run 2.6 seconds behind, but at
the right rate.

It is configured as a broadcastclient.  There is one stratum 1 system
braodcasting on the subnet for which this client should sync to.

Something must have gone very wrong when this client tried to
calculate the delay when it started up.

Should the system ever try to re-calibrate the broadcast delay once
running or will it stay the same as long as the broadcaster keeps
broadcasting?  Not even once a hour/day?

It seems very wrong to accept a negative broadcast delay, shoudn't
ntpd check for this and try again or reject the peer?

Info below:

version is ntpq 4.2.4p3.


card9# ntpdate -q card8
server 172.16.7.1, stratum 1, offset 2.614497, delay 0.02570
19 Oct 18:57:28 ntpdate[1387]: step time server 172.16.7.1 offset 2.614497 sec

card9# ntpq -c peers
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*card8           .EXTL.           1 u    1   16  377    0.064    2.029   0.020

card9# ntpq -c "pstatus 41011"
assID=41011 status=1614 reach, sel_sys.peer, 1 event, event_reach,
srcadr=card8, srcport=123, dstadr=172.16.8.1, dstport=123, leap=00,
stratum=1, precision=-20, rootdelay=0.000, rootdispersion=10.422,
refid=EXTL, reach=377, unreach=0, hmode=6, pmode=5, hpoll=6, ppoll=4,
flash=00 ok, keyid=0, ttl=0, offset=2.029, delay=0.064,
dispersion=0.246, jitter=0.020,
reftime=cac37c8e.6b04779a  Fri, Oct 19 2007 18:57:18.418,
org=cac37c9a.6ac923d1  Fri, Oct 19 2007 18:57:30.417,
rec=cac37c97.cd7c2a03  Fri, Oct 19 2007 18:57:27.802,
xmt=cac36ac1.dfef554c  Fri, Oct 19 2007 17:41:21.874,
filtdelay=     0.06    0.06    0.06    0.06    0.06    0.06    0.06    0.06,
filtoffset=    2.03    2.00    2.04    2.05    2.02    2.04    2.06    2.04,
filtdisp=      0.00    0.26    0.53    0.77    0.99    1.26    1.49    1.76

card9# ntpdc -c "showpeer card8"
remote 172.16.7.1, local 172.16.8.1
hmode control, pmode mode#108, stratum 1, precision -20
leap 00, refid [EXTL], rootdistance 0.00000, rootdispersion 0.01042
ppoll 4, hpoll 6, keyid 0, version 4, association 41011
reach 377, unreach 0, flash 0x0000, boffset -2.61241, ttl/mode 0
timer 0s, flags system_peer
reference time:      cac37c8e.6b04779a  Fri, Oct 19 2007 18:57:18.418
originate timestamp: cac37c9a.6ac923d1  Fri, Oct 19 2007 18:57:30.417
receive timestamp:   cac37c97.cd7c2a03  Fri, Oct 19 2007 18:57:27.802
transmit timestamp:  cac36ac1.dfef554c  Fri, Oct 19 2007 17:41:21.874
filter delay:  0.00006  0.00006  0.00006  0.00006 
               0.00006  0.00006  0.00006  0.00006 
filter offset: 0.002029 0.002000 0.002042 0.002048
               0.002016 0.002036 0.002062 0.002042
filter order:  0        1        2        3       
               4        5        6        7       
offset 0.002029, delay 0.00006, error bound 0.01569, filter error 0.00449

-- 
Dave Johnson
Starent Networks




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