[ntp:questions] Polling time backoff

David Lord snews at lordynet.org
Tue Jan 12 02:46:32 UTC 2010


shane-dated-2009 at csy.ca wrote:
>> Dave Hart <davehart at gmail.com> writes:
>>
>>> On Nov 28, 11:52=A0pm, shane-dated-2... at csy.ca wrote:
>>>> Just wondering if there is anything in particular which would keep ntpd
>>>> polling its servers every 64s
>>>>
>>>> server 127.127.20.0 minpoll 4 prefer
>>>> fudge 127.127.20.0 flag3 1 flag2 0
>>> The refclock is holding the poll interval down.  You have to use
>>> minpoll on the remote server lines to force them to a longer poll
>>> interval in the presence of a reflock with a smaller poll interval.
>> Is that really right? I thought that all of the clocks had their poll intervals
>> determined independently. YOu seem to be saying they do not, that the poll
>> intervals are "universal" the smallest poll interval for any server is used.
>> On my system that is certainly not true
> 
> Hmm, I think Richard Gilbert's post was pretty well spot on, watching the
> poll last night, it did go as high as 512 at around 2 AM for some of the
> servers. I just unconfig'd the refclock to see if that's making a difference
> but so far, polling is still at 64s. A bit odd, my connection to the net
> isn't terrible, res. cable connection but delays are decent. It's asymmetric
> though which I understand can give ntpd some grief.

I may be talking rubbish but ntpd here seems to need to get
within a certain tolerance before poll increases. At 64s
there may be too much jitter whilst at higher initial polls
this appears to be smoothed out and poll can increase
further.

An alternative to increase of minpoll may be to set mindist
above default. A higher minpoll can mean a longer period
before ntpd settles down, but on my setup I have a couple of
local peers that I'm polling as fast as needed.

> 
> I have my net speed throttled slightly below upstream max so I can do packet
> prioritization and have ntp packets pretty high up in the queues so it's not
> like they're being held up in the modem buffers either.

Same here and it doubled my upload speed and still leaves a bit
of headroom for prioritised traffic. I'm on 2Mbit/288kbit adsl.

David

> 
> Shane




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