[ntp:questions] server and peer lines correct?

Charles Swiger cswiger at mac.com
Mon Apr 7 20:08:07 UTC 2014


Hi--

On Apr 7, 2014, at 12:12 PM, Harlan Stenn <stenn at ntp.org> wrote:
> Why would you not want to iburst all of the servers?

iburst helps to populate the reachability field quickly.
That reduces the interval it takes for an NTP server to move from:

associd=0 status=c012 leap_alarm, sync_unspec, 1 event, freq_set   =>
associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync

...which is the transition needed before clients of the server will trust it for time.

However, the transition doesn't happen any faster if you only use one server with iburst,
or with all of the server lines.  The data I've seen doesn't show any significant
differences to the local clock variables like frequency, sys_jitter, clk_jitter.

(My offset is bouncing around because ntpd is being started up using -g.)

Regards,
-- 
-Chuck

PS: For more detailed comparison; let's consider three examples.  #1; start with:

$ cat /etc/ntp.conf
server 17.254.0.27	# aka time1.apple.com
server 17.254.0.28	# aka time2.apple.com
server 17.254.0.31	# aka time3.apple.com
server 17.151.16.20	# aka time4.apple.com

Restart ntpd.  Run:

repeat 100; do; sleep 10; ntpq -npcrl; done

It takes ~200 seconds before the transition happens:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*17.254.0.27     17.150.142.121   2 u    6   64   17    3.903   14.965   0.082
 17.254.0.28     17.150.142.121   2 u  136   64   14   55.557   40.997   2.545
 17.254.0.31     17.150.142.121   2 u   67   64    6   41.580   33.254   4.612
 17.151.16.20    17.107.131.11    2 u   67   64    7    3.183   14.882   0.109
associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
version="ntpd 4.2.6 at 1.2089-o Fri May 28 01:20:53 UTC 2010 (1)",
processor="x86_64", system="Darwin/12.5.0", leap=00, stratum=3,
precision=-20, rootdelay=4.911, rootdisp=980.970, refid=17.254.0.27,
reftime=d6ed797f.fcf6fd16  Mon, Apr  7 2014 12:22:39.988,
clock=d6ed7985.0fb84e27  Mon, Apr  7 2014 12:22:45.061, peer=39832, tc=6,
mintc=3, offset=14.965, frequency=-11.064, sys_jitter=0.082,
clk_jitter=5.291, clk_wander=0.000

	======

#2; start with:

$ cat /etc/ntp.conf
server 17.254.0.27 iburst
server 17.254.0.28
server 17.254.0.31
server 17.151.16.20

Restart ntpd.  Run:

repeat 100; do; sleep 10; ntpq -npcrl; done

...except there's no need, since ntpd claims to be synced immediately:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*17.254.0.27     17.150.142.121   2 u    6   64    1    3.301  -33.495   0.077
 17.254.0.28     .INIT.          16 u    -   64    0    0.000    0.000   0.000
 17.254.0.31     .INIT.          16 u    -   64    0    0.000    0.000   0.000
 17.151.16.20    17.107.131.11    2 u    8   64    1    3.198  -33.747   0.001
associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
version="ntpd 4.2.6 at 1.2089-o Fri May 28 01:20:53 UTC 2010 (1)",
processor="x86_64", system="Darwin/12.5.0", leap=00, stratum=3,
precision=-20, rootdelay=4.308, rootdisp=251.489, refid=17.254.0.27,
reftime=d6ed7a30.28ff9651  Mon, Apr  7 2014 12:25:36.160,
clock=d6ed7a36.32b6d90d  Mon, Apr  7 2014 12:25:42.198, peer=31035, tc=6,
mintc=3, offset=-33.495, frequency=-11.068, sys_jitter=0.077,
clk_jitter=11.076, clk_wander=0.001

	======

#3; start with:

$ cat /etc/ntp.conf
server 17.254.0.27 iburst
server 17.254.0.28 iburst
server 17.254.0.31 iburst
server 17.151.16.20 iburst

Restart ntpd.  Run:

repeat 100; do; sleep 10; ntpq -npcrl; done

...except there's no need (again), since ntpd becomes synced immediately:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*17.254.0.27     17.150.142.121   2 u    8   64    1    3.246  -28.288   0.597
 17.254.0.28     .INIT.          16 u    -   64    0    0.000    0.000   0.000
 17.254.0.31     .INIT.          16 u    -   64    0    0.000    0.000   0.000
 17.151.16.20    17.107.131.11    2 u    5   64    1    2.787  -28.584   0.070
associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
version="ntpd 4.2.6 at 1.2089-o Fri May 28 01:20:53 UTC 2010 (1)",
processor="x86_64", system="Darwin/12.5.0", leap=00, stratum=3,
precision=-20, rootdelay=3.798, rootdisp=985.368, refid=17.254.0.27,
reftime=d6ed7adc.97957b98  Mon, Apr  7 2014 12:28:28.592,
clock=d6ed7ae6.03b8c8dc  Mon, Apr  7 2014 12:28:38.014, peer=51228, tc=6,
mintc=3, offset=-28.318, frequency=-11.064, sys_jitter=0.787,
clk_jitter=10.012, clk_wander=0.000

[ Perhaps I should retry with ntpd 4.2.7p439 at 1.2483-o.  And track the variables over a longer period of time, perhaps several hours.... ]


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