# NTP maxpoll limits

Regarding NTP's maxpoll configuration attribute, many resources state:

The maximum poll interval defaults to 10 (1,024 s), but can be increased by the maxpoll option to an upper limit of 17 (36.4 h)

However I couldn't find references for hacing it lower than the defaul value of 10 (1,024s). Can it be set for a lower value? say to 6?

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You could just use Science and test it... –  mgorven May 31 '12 at 21:26
@mgorven - I'm trying to, haven't figured out how to validate it for sure with the monitoring app. besides, I believe in having stuff documented for the sake of others, and the stack exchange platform is ideal for that. If I will manage to find the answer, I will share of course. –  Jonathan Jun 1 '12 at 5:47

According to the ntp.conf(5) man page, the lowest value of maxpoll is 4. This setting requires that minpoll is set to 3.

minpoll minpoll, maxpoll maxpoll

These options specify the minimum and maximum poll intervals for NTP messages, in seconds as a power of two. The maximum poll interval defaults to 10 (1,024 s), but can be increased by the maxpoll option to an upper limit of 17 (36.4 h). The minimum poll interval defaults to 6 (64 s), but can be decreased by the minpoll option to a lower limit of 4 (16 s). These option are valid only with the server and peer commands.

Edit: This is how it is implemented in ntp-4.2.6p5/ntpdc/ntpdc_ops.c:1433:

if (minpoll < NTP_MINPOLL || minpoll > NTP_MAXPOLL ||
maxpoll < NTP_MINPOLL || maxpoll > NTP_MAXPOLL ||
minpoll > maxpoll) {
fprintf(fp, "***min/max-poll must be within %d..%d\n",
NTP_MINPOLL, NTP_MAXPOLL);
res = TRUE;
}


Where NTP_MINPOLL is 3 and NTP_MAXPOLL is 17.

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they are referring to minpoll not maxpoll. This is exactly the reason for my question –  Jonathan Jun 1 '12 at 8:38
You can set minpoll 3 and maxpoll 4 if I understood that correctly. –  Oliver Jun 1 '12 at 9:11
Use the source, Luke. –  Oliver Jun 1 '12 at 9:25
Now you're talking! :) –  Jonathan Jun 1 '12 at 10:19