Re: chrony question about -x option

On Mon, Oct 24, 2022 at 12:14 PM Miroslav Lichvar <[email protected]>
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