[ntp:questions] Re: What does 73.78.73.84 refer to?

Tim tim at mail.localhost.invalid
Wed Nov 9 11:32:43 UTC 2005


Tim:

>> as it's clock via the DHCP daemon (a local server for the LAN).  The
>> local clock setting is a manual thing left in so NTP carries on running
>> if the network is down.

David Woolley:

> NTP continues to run regardless of whether or not the network is up, and
> regardless of whether there is a local clock configured.

There's this little glitch with the current implementation, whether that
be NTP or NTP on Fedora:

If your internet connection goes down, NTP stops using it to connect to
servers.  Later, when your internet connection returns, it still makes no
attempt to connect to internet servers through the returned connection.

So, once outside connection is lost, manual intervention is required to
restart the NTP server.  I just put a restart script into an ip-up.local
script which is run after a PPP connection goes up.  But otherwise you end
up with a computer no better than if you *never* had NTP on it.

> Local clocks should never be used on leaf nodes.

I'd debated the wisdom of including a local clock, but it seems without at
least one clock that NTP can use, it stops working if it loses network
connectivity with other NTP servers.

> Also, it is conventional to use a stratum more like 10, to minimise the
> damage if anything does try and synch to a machine using a free running
> local clock.

I'd been advised 9, so that one served as a master (being at least one
stratum higher than most individual lost sync clients).  So they all
stayed together, rather than be able to drift apart as they all sat
isolated at stratum 10.

> When used as a fallback on servers, local clocks compromise the ability to
> estimate the uncertainty in the time, because root dispersion and delay
> are reset when the local clock is selected.

I'll have to read more on that, because I don't understand the jargon.

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