[ntp:questions] NTPD concurrent clients limit

Richard B. Gilbert rgilbert88 at comcast.net
Wed Jul 30 11:21:49 UTC 2008

j. wrote:
> Hi all,
> I'm testing an embedded linux device, which implement an NTP server,
> based on the ntpd demon.
> It looks like ntpd accepts only a limited number of requests from a
> test clientIi've set up.
> Do you know if there's such limit or what's the logic behind it?
> Maybe ntpd rejects bursts of requests coming from the same IP?
> Thanks in advance,
> Gianandrea Gobbo.

If you poll the server continuously at intervals of less than 64 
seconds, most modern NTP servers will send you a "Kiss of Death" packet.
Polling this frequently is considered abusive!  It's also unnecessary, 
NTP is designed to work with poll intervals between 64 seconds and 1024 
seconds and will adjust its poll interval within that range as needed.

There are two exceptions to the above.  You may specify the "iburst" 
keyword for a server and NTPD will send an INITIAL burst of eight 
request packets at intervals of two seconds.  This is designed for fast 
startup.  After the initial burst, polling continues at intervals 
between 64 and 1024 seconds.

If you are using a dialup telephone connection for short periods three 
or four times a day, you may specify the "burst" keyword which sends 
eight requests two seconds apart at EACH poll interval.  "Burst" is to 
be used ONLY for brief periods with LONG intervals between them!

It is customary to request permission from the owner of the server 
before using "burst".

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