[ntp:questions] Re: ntpd on Windows XP

Steve Kostecke kostecke at ntp.isc.org
Wed Mar 23 20:16:37 UTC 2005


On 2005-03-23, Kemal Oral CANSIZLAR <ocansizlar at comcast.net> wrote:

> "David J Taylor"
> <david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk> wrote in
> message news:lsi0e.3994$Ab.1753 at text.news.blueyonder.co.uk...
>
>> Steve Kostecke wrote:
>>
>>> burst When the server is reachable, send a burst of eight packets
>>> instead of the usual one.

Another way of describing burst is that it causes ntpd to send a burst
of eight packets to a remote time server each time that remote time
server is polled.

>>> iburst When the server is unreachable, send a burst of eight packets
>>> instead of the usual one.

Another way of describing iburst is that it causes ntpd to send a burst
of eight packets to a remote time server when ntpd has lost contact with
that time server for an extended period of time or when ntpd has never
contacted that server before (e.g. at start-up).

<snip>

>>> It seems pretty clear if you understand what "reachable" means.
>>
>> I disagree. Unreachable sounds like a fault condition, something that
>> would not normally be encountered.

A remote time server is considered to be unreachable when ntpd has not
received NTP packets from that remote time server for so long that none
of the bits in the Reachability Register are set.

>From RFC-1305:

"Reachability Register (peer.reach): This is a shift register of WINDOW
bits used to determine the reachability status of the peer, with bits
entering from the least significant (rightmost) end. A peer is
considered reachable if at least one bit in this register is set to
one."

The Reachability Register is updated at each poll interval.

>>Reachable sounds like a normal operating mode.

Yes. A remote time server is reachable when your ntpd regularly receives
packets from it. 

> That's exactly what I understood from the text; I think it is
> misleading for an outsider.
>
>> However, if phrases like:
>>
>>  burst only use for debugging, not for normal usage

burst is intended to be used in situations where packet loss is a
problem.

>>  iburst typically used when NTP is starting up so as to speed initial
>> synchronisation

iburst will be used whenever a remote time server becomes unreachable,
not just when ntpd is first started.

>> were added to the text it would make it much clearer what the
>> intended purpose of these options was.

The document we're discussing is maintained by Dr. Mills. Please forward
your suggested revisions to him.

You are also welcome to contribute material to the Community Supported
Documentation at http://ntp.isc.org/support

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



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