[ntp:questions] Good ntp.conf for a public server?

Chuck Swiger cswiger at mac.com
Tue May 10 18:09:55 UTC 2011


Hi, Jim--

On May 10, 2011, at 10:46 AM, Jim Kusznir wrote:
> I'm setting up an NTP server with a GPS-PPS hardware clock, and I am
> wondering what settings are "recommended".
> 
> My time server is currently accessible at:
> 
> time.eecs.wsu.edu
> 
> Its a P4-2.4Ghz using the shm driver pulling a PPS feed from a SEL
> 2407 GPS clock.

It would be helpful to show the peers scoreboard, but either a firewall or your config is blocking this:

% ntpq -p -crv time.eecs.wsu.edu
time.eecs.wsu.edu: timed out, nothing received
***Request timed out

> I'm mostly concerned about correct permissions and any multicast or
> other options I should turn on (or off) for public use.

OK.  It's likely that the wiki page here will help:

  http://support.ntp.org/bin/view/Support/AccessRestrictions

NTP multicast isn't that commonly used, especially over the WAN.
(I've seen one or two networks using it locally, though.)

> I'm also curious about what the expected load and its effect on
> accuracy for a public pool server.

Most NTP is tiny (~70 byte) UDP packets; even fairly high load of 100+ packets per second won't require much in the way of network bandwidth or CPU load on the box.  In any event, you can assign a bandwidth to servers in the pool, which govern how often they are listed when clients lookup pool servers.  You can adjust this to suit your preferences.

In times past, I was seeing about 15 pps normally, with peaks of ~50 pps with a 1.5 Mbit/s setting.

There is minimal impact on accuracy from client even for a stratum-2 or higher server which needs to talk with primary NTP timesources over the network; for something which is a stratum-1 with a PPS discipline, you shouldn't see any impact to timekeeping accuracy.

Regards,
-- 
-Chuck




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