[ntp:questions] Re: restrict in ntpdc

Richard B. Gilbert rgilbert88 at comcast.net
Wed Nov 3 14:43:30 UTC 2004

Nagy Bela wrote:

>First, thanks for your help.
>>Assuming that you're talking about the ntpd running on the dial-up
>>system... Just list the remote time servers in your /etc/ntp.conf and
>>use /etc/ppp/ip-up to restart ntpd. Your ntpd will sync to a remote time
>>server in ~15.30 seconds if you use the 'iburst' option on the server
>>lines in your /etc/ntp.conf.
>I heard the using iburst without prior permission is highly unfriendly.
>And I dont have permissions.
I think you are confusing burst with iburst.   The documentation on 
these features is not as clear as it might be.

Burst is special purpose hack that was never intended for general use 
and should not be used without special permission from the owner of the 
server.  Burst causes ntpd to send eight request packets at every 
polling interval.  This, of course, places eight times the normal load 
on the server which is the reason permission is required.

Iburst is used to initialize an association quickly.   It does this by 
sending eight request packets at intervals of two seconds.   The eight 
replies fill the clock filter pipeline and allow ntpd to make a 
reasonable estimate of the round trip delay to each server and the 
correct time.  ntpd will select a synchronization source in about 
sixteen seconds instead of eight minutes.  After the initial burst of 
packets, the succeeding packets will be sent at the normal interval of 
sixty-four seconds.

Iburst is particularly appropriate for a dialup connection; ntpd 
acquires enough information in the first sixteen seconds to begin 
synchronizing your clock.  A ten or fifteen minute phone call should be 
enough to bring your clock into fairly good synchronization if it was 
close to being correct initially.

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