[ntp:questions] broadcast client

Danny Mayer mayer at ntp.isc.org
Sat Nov 22 13:46:02 UTC 2008


Normally I would not respond to a 2 month old message but I need to
correct some things here that were written.

Unruh wrote:
>>> connected via 1 Gbps switch.  The network is lightly loaded and I
>>> configured the clients as such
>>>
>>> server ntp minpoll 4 maxpoll 4 iburst
> 
>> Dave Mills, please note, yet another non-believer in the NTP algorithms.
> 
> What this has to do with not believing in the algorithm I have no idea. If
> ntp runs from a refclock that is EXACTLY the default behaviour.

This is NOT the default behavior. minpoll defaults to 4 and maxpoll
defaults to 10 and you should NOT change them unless you understand the
discipline arguments and how these changes affect the discipline.

> Running on
> a local private network where you are referencing your own server, that
> behaviour is also fine. The reason for the backup to long poll intervals is
> a) to save the public servers from flooding, and b)to discipline the local
> clock's drift rate in case there are long periods of disconnection from the
> net. If you have constant connection and it is your own server, neither of
> those apply, and short polling is better. 
> 

a) This is not correct. It has nothing to do with public servers. In
addition I've conducted tests where I've fired 100's of packets per
second and not even noticed any affect on other work on the target
server. In the case of your own servers you won't notice the traffic in
any event.

b) is also incorrect. The purpose of the backup is in the algorithms and
has to do with oversampling. In this case you are making your local
clock less stable rather than more stable. More is not necessarily
better and the sooner that people understand this the fewer problems
that they will have.


> I have no idea why you make the first claim. Yes, the rate will vary as the
> network rates vary, but who cares. The purpose is to discipline the TIME,
> not the rate.

No. The purpose is to discipline both.

> And short polls discipline the time better.

It doesn't.

> Rate discipline
> is overrated because of the rate variations due to temperature changes
> during the day anyway.
> 

No, it is not overrated unless you are oversampling like you are
recommending.

Danny




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