Shippable ntp.conf files for the HOWTO

Hal Murray hmurray at
Thu Jun 9 08:09:25 UTC 2016

gem at said:
>> Are you confusing iburst with burst?
> Probably.  The official descriptions are essentially identical, and the
> iburst seems a tad nicer to my eye.  But we know that reading between the
> lines is not useful with NTP doc. :-( 

iburst happens at startup time.  That includes restart for things like 
plugging an Ethernet cable in.  It lets ntpd get (re)started (much) faster.

burst happens every time it decides to poke the remote server, aka at the 
poll interval.

If you are using your servers you can do anything you want.  If you are using 
a free resource (pool servers or public servers like NIST), you should be 
polite.  I don't know of any official pool rules.  One a minute is generally 
considered OK.  I think I've seen something like that on the NIST web site.

Using iburst is generally considered reasonable.  The default server side 
rate limiting will allow iburst but probably kick in if you are behind NAT 
and restart 2 or more systems using iburst at the same time.

burst has a bad reputation.  If I read things correctly, the size of the 
burst is adjusted to not go over the equivalent minpoll rate.  There is a 
ceiling of 8.  So I don't see any problem.  Neither do I see any reason to 
use it unless you are working with dialup or very low bandiwidth radio links.

Even without any bursting, reducing the polling interval below the default 6 
with minpoll/maxpoll is not friendly to pool/public servers.

Similarly, if you have lots of systems, you should setup your own server (or 
a few of them) and have most of your systems get time from your local servers.


If I'm looking for documentation on something like iburst, I generally try 
something like:
  grep iburst docs/ -rl
And then poke around in the hits.

These are my opinions.  I hate spam.

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