[ntp:questions] simple nt.conf cases for ntp-client

ardi peter.knezel at gmail.com
Thu Jan 23 07:29:25 UTC 2014


Below are described some basic cases for ntp.conf on ntp-client:

a)
In the simplest case of ntp-client the following ntp.conf is defined:

restrict default noquery nomodify notrap
restrict 127.0.0.1
driftfile /var/lib/ntp/ntp.drift
server xx.xx.xx.xx minpoll 4 maxpoll 4 
restrict xx.xx.xx.xx

Why should i need the restrict line xx.xx.xx.xx?
What does the first restrict line means?

b1)In case using 2 ntp-servers from which my ntp-client can get time,
is my ntp-client taking time from xx.xx.xx.xx
and if this server is not reachable then from xx.xx.xx.yy?


restrict default noquery nomodify notrap
restrict 127.0.0.1
driftfile /var/lib/ntp/ntp.drift
server xx.xx.xx.xx minpoll 4 maxpoll 4 
server xx.xx.xx.yy minpoll 4 maxpoll 4 
restrict xx.xx.xx.xx
restrict xx.xx.xx.yy

What happens if xx.xx.xx.xx comes up again?
Does client take time again from the xx.xx.xx.xx?

b2)
What does prefer do in this case b2)?
Is there any difference between b1) and b2) case?

restrict default noquery nomodify notrap
restrict 127.0.0.1
driftfile /var/lib/ntp/ntp.drift
server xx.xx.xx.xx minpoll 4 maxpoll 4 prefer
server xx.xx.xx.yy minpoll 4 maxpoll 4 
restrict xx.xx.xx.xx
restrict xx.xx.xx.yy

b3)
what about this case b3) below?
Is time taken for the ntp-client according to order of lines - i mean the xx.xx.xx.xx is taken as time source?
or the 2nd server xx.xx.xx.yy is preferred?

restrict default noquery nomodify notrap
restrict 127.0.0.1
driftfile /var/lib/ntp/ntp.drift
server xx.xx.xx.xx minpoll 4 maxpoll 4 
server xx.xx.xx.yy minpoll 4 maxpoll 4 prefer
restrict xx.xx.xx.xx
restrict xx.xx.xx.yy

Thanks for the explanation.
Peter



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