[chrony-users] Polling intervals between peers

[cfanygapa <cfanygapa@xxxxxxx>]

Hi

I am using 4 own (internal) Chrony servers which are synced from web 
(external) NTP sources.
Additionally, my own servers are all in peer relation to each other.

NTP’s documentation 
(https://www.eecis.udel.edu/~mills/ntp/html/assoc.html#poll) has the 
following sentence regarding peers:
“With symmetric modes the most stable behavior results when both peers 
are configured in symmetric active mode with matching poll intervals of 
6 (64 s)”

Does the same recommendation apply for peers set up in Chrony?
If yes, does it have any explanation why polling=6 is better for peers 
instead of something like “minpoll 2 maxpoll 4 polltarget 30” if peers 
are in local network with short distance between each other?

I’ve done a simple test ... configured my sever A to peers B, C and D 
with “minpoll 2 maxpoll 6 polltarget 30” to observe how polling will 
change.
A B C are in the same subnet/VLAN (Peer delay ~0.0001s), D is in distant 
backup localization but still with good link and short distance (Peer 
delay ~0.001s). With mentioned “minpoll 2 maxpoll 6 polltarget 30” 
settings, A->B and A->C (so polls to very close hosts) ends up with max 
Poll=2 for most of the time while A->D (so to distant peer) always raise 
towards Poll=6.
Is that explainable somehow or I am looking into non-existing issue and 
I should go to sleep leaving defaults and letting Chrony to do its 
calculate job? 

Example sources output:

MS Name/IP address         Stratum Poll Reach LastRx Last sample
=============================================================================== 

....
=+ b.foo.bar.net                 2   2   377     5    +31us[  +31us] ± 
5290us
=+ c.foo.bar.net                 2   2   377     4    +48us[  +48us] ± 
5128us
=+ d.foo.bar.net                 2   6   377    30    -32us[  -30us] ± 
6927us

Example sourcestats output:

Name/IP Address            NP  NR  Span  Frequency  Freq Skew Offset  
Std Dev
============================================================================== 

....
b.foo.bar.net               8   7    29     -1.290      3.407 +37us    16us
c.foo.bar.net              46  22   181     +0.007      0.124 +40us    13us
d.foo.bar.net              30  12   26m     +0.031      0.065 -236us   
 43us


On the other hand, I would like to understand what I’m doing as whole 
topic of minpoll/maxpoll/polltarget is still a bit non-clear to me 
despite of pretty good info in chrony’s FAQ page.
Should I simply observe “NP” + “Span” fields as an indication of any 
poll values tuning?

Thanks in advance
Tom

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