Re: [chrony-dev] Running chronyd without syncing system clock

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

On Fri, 24 Feb 2012, Leo Baltus wrote:
> I am not saying that multiple processes should serve a single clock.
>
> Let me try some good old ascii art:
>
>        uplink                   local nets
>   pool  ---   ntp-only-server1     ---     ntp-client
>               ntp-only-server2     ---     ntp-client
>               ntp-only-server3     ---     ntp-client
>                                    ---     ntp-client
>
> The pool is a set of ntp-servers outside my network. Inside my network I
> have 4 servers (hardware) each running an ntp-client synchronizing to 3
> ntp-only-servers (chronyd instances). The ntp-only servers run on the

No idea what that means.

> same hardware as the ntp-clients but do not sync the system clock. Each

That makes no sense. Ntp is a procedure for sycnchronising the local clock to
a remote clock by periodically comparing the remote clock to the local clock.
It has absolutely no idea of time. It cannot serve time. It is a device for
comparing two clocks which do have an idea of time. It is like a weighing
machine, and you are talking about a  balance weighing machine onto whose pans you
place nothing, and then saying it is supposed to tell you want weight is. It
cannot.


> ntp-only server has its own ip address unrelated to the server's ip
> address. Some hardware is running ntp-clients only. The ntp-clients do
> sync the system clock. Some ntp clients may even be outside my networks.
>
> The ntp-only servers can now bind to its own IP address for *both*
> serving ntp as well as sending udp packets to the pool. This way there
> is now way for the pool or the ntp-clients to see on what hardware the
> ntp-only server is running. We call this IP-virtualization, no need for
> virtual machines. This is ideal if there are firewall administrators
> who have a policy of only allowing traffic based on single IP numbers
> rather than ranges. Also this works with IPv6 as well. Any solution that
> requires NAT is a no go as far as we are concerned.
>
> So for the ntp-only servers to function properly they have to have an
> accurate system clock which they cannot set. This may be a catch22 on

Why? What is this for in your scheme?

> startup, however I assume that not all local clocks will be off so an
> ntp client can still pick an other ntp-only source.
>
> I am approaching this from an networking/firewalling/administration
> point of view and hope not to introduce all sorts of timing issues which
> I am sure you have thought about much harder than I did.
>
> In the mean time I have prepared a patch to see if i can get this
> working. Any thoughts about testing scenarios?

--
William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1     |      and Gravity       |  www.theory.physics.ubc.ca/

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