[ntp:questions] peer command and clusters

Steve Kostecke kostecke at ntp.org
Mon Mar 28 19:37:20 UTC 2011


On 2011-03-28, Florin Andrei <florin at andrei.myip.org> wrote:

> On 03/26/2011 08:46 AM, Dave Hart wrote:
>
>> You probably want iburst on each of those server lines, to sync the
>> clock in under 15 seconds instead of a few minutes.
>
> I thought that was frowned upon, to use iburst with public servers?
>
> (I do use iburst, from all the other machines to the internal NTP
> servers.)

'burst' is a permanent multiplier which causes a burst of packets to be
sent at expiration of _every_ poll period.

'iburst' is a temporary multiplier which causes a burst of packets to be
sent at expiration of each poll poll period _only_ when a remote time
server is unreachable.

The stable release uses bursts of 8 packets while ntp-dev uses bursts of
6 packets.

Documentation references:

Current Stable --> http://doc.ntp.org/4.2.6p3/confopt.html

"burst -- When the server is reachable, send a burst of eight packets
instead of the usual one. The packet spacing is normally 2 s; however,
the spacing between the first and second packets can be changed with
the calldelay command to allow additional time for a modem or ISDN call
to complete. This option is valid only with the server command and type
s addressesa. It is a recommended option when the maxpoll option is
greater than 10 (1024 s).

iburst -- When the server is unreachable, send a burst of eight packets
instead of the usual one. The packet spacing is normally 2 s; however,
the spacing between the first and second packets can be changed with the
calldelay command to allow additional time for a modem or ISDN call to
complete. This option is valid only with the server command and type s
addresses. IT IS A RECOMMENDED OPTION WITH THIS COMMAND." (emphasis
added)

NTP Dev --> http://www.eecis.udel.edu/~mills/ntp/html/confopt.html

"burst -- When the server is reachable, send a burst of packets instead
of the usual one. This option is valid only with the server command and
type s addresses. It is a recommended option when the maxpoll option is
greater than 10 (1024 s). Additional information about this option is on
the Poll Program page.

iburst -- When the server is unreachable, send a burst of packets
instead of the usual one. This option is valid only with the server
command and type s addresses. IT IS A RECOMMENDED OPTION WITH THIS
COMMAND. Additional information about this option is on the Poll Program
page." (emphasis added)

Poll Program page http://www.eecis.udel.edu/~mills/ntp/html/poll.html

"The burst options can result in increased load on the network if not
carefully designed. Both options are affected by the provisions
described on the Rate Management and the Kiss-o'-Death Packet page. In
addition, when iburst or burst are enabled, the first packet of the
burst is sent, but the remaining packets sent only when the reply to the
fist packet is received. If no reply has been received after a timeout
set by the minpoll option, the first packet is sent again. This means
that, even if a server is unreachable, the network load is no more than
at the minimum poll interval."

-- 
Steve Kostecke <kostecke at ntp.org>
NTP Public Services Project - http://support.ntp.org/




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