[ntp:questions] Ntp in peer configuration

Steve Kostecke kostecke at ntp.org
Sat Apr 12 05:27:23 UTC 2008


On 2008-04-09, Ginni Misra <misraginni at yahoo.com> wrote:

>   I am trying to use NTP in peer configuration. 

In a time island.

> 5. All machines on the network should have a common notion of time
> (offset not larger than 20ms) - not necessarily the 'correct' time(no
> need of getting time from external servers)

NTP synchronizes clocks to a _common_ _time_ _base_.  The time base that
is customarily used is UTC. UTC is ubiquitous (e.g. available via the
Internet, GPS, GPS over CMDA, HF Radio, ATCS dialup) and is relatively
inexpensive compared to the cost of generating a local time base of
similar stability.

>So, to solve the above, I configured the 1st machine on the network
>with reference clock as LOCL. So, when the 2nd device comes up, ntpdate
>is successful. However, this introduces additional complexity like: 2

You're doing this the hard way.

An "Orphan mesh" (or web) is the preferred way to handle your situation;
assuming that you are using NTP 4.2.x.

Orphan mode is enabled by adding the following line to the ntp.conf of
all of your systems:

	tos orphan 5

Then you need to choose the mode for your mesh: unicast, broadcast, or
multicast. Each system in the mesh needs to be configured to poll all of
the other systems.

You may wish to consult the following news-group articles for
configuration information:

https://lists.ntp.org/pipermail/hackers/2007-March/002809.html
http://www.mail-archive.com/questions@lists.ntp.org/msg00986.html

Those articles do not address setting up a unicast (conventional
client/server) mesh. If you just have a small number of systems this may
be the the easiest solution as it avoids configuring NTP authentication.

Each system in a 4 node mesh could have an ntp.conf which looks like
this:

-----------------------------------8X-----------------------------------

driftfile /path/to/drift.file
tos orphan 5
server A iburst
server B iburst
server C iburst
server D iburst

-----------------------------------8X-----------------------------------

Make sure that ntpd is started with '-g' so that the initial time can
make an unlimited step.

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




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