Re: [chrony-users] chrony question about -x option

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On Mon, Oct 24, 2022 at 12:14 PM Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
On Fri, Oct 21, 2022 at 06:07:19PM +0200, Hubert Verstraete wrote:
>  Hello
>
> I want to use chrony on a host "A" connected to the Internet which should
> act only as a kind of NTP relay to serve the time from an NTP server on the
> Internet to another host "B" on the local network. But I don't want to set
> the system clock of host "A" with this Internet time.
> To achieve this, I plan to start chrony on host "A" with the option -x.
>
> The system clock of host "A" is controlled by another process getting the
> time from the local network.
> Will the Internet time served by host "A" be impacted by the fact that the
> system clock is adjusted by the other process ?

Yes, it will. How much it depends on the stability of the system clock
synchronization. You should make sure it's not synchronized to
something synchronizing directly or indirectly to the chronyd -x
instance. That would work poorly due to a synchronization loop.

OK, then it's not a good idea to use the option -x.
 
> The host "B" needs to synchronize to the raw Internet time in order to keep
> the best accuracy.

Why does host A not have the same requirement and why does B not send
requests directly to Internet?

In my network topology, there are several local networks.
Only the first network with host A can connect to Internet.
The network with host B is completely isolated from Internet (NAT is not allowed).
I have the constraint that host B must synchronize all the hosts of all local networks.

That's why I wanted to use chrony on host A as a relay of the NTP time. I thought chrony -x could be the solution but it's not.
Is there something in chrony which listens for incoming NTP packets on one inbound interface and forwards them on an outbound interface ?
Or I could maybe implement a server on host A to relay NTP packet to the NTP server on Internet...

Thanks
Hubert


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