Re: [chrony-users] chronyc tracking question

[Miroslav Lichvar <mlichvar@xxxxxxxxxx>]

On Wed, Jul 26, 2017 at 06:15:13PM -0400, Chris Perl wrote:
> I'm pretty sure the interleaving gets messed up and I don't wind up
> getting back the timestamp from the previous exchange (i.e. I'm losing
> out on the hardware timestamping of t3 on the server).  I think that
> accounts for the extra 15us that I'm seeing.

Your analysis is correct. 

> Is this something that should work, or is the thing I'm trying to do
> not intended to work?

With the current implementation, interleaved mode with multiple
clients on the same IP address is not expected to work. The man page
mentions this issue with multiple clients behind NAT.

Modifying the code to keep track of individual ports wouldn't help,
because clients usually change their port between requests.

The timestamps could be separate from IP addresses completely. This
would allow multiple clients on the same IP address, or even clients
that change their address between requests. However, a broken client
sending too many request would be able to flush timestamps that belong
to other clients. I'm not sure which is worse. There may be a better
way to do this.

As a workaround in your case, you could configure the monitoring
client as a peer or you could run a second server instance on a
different port serving local time.

-- 
Miroslav Lichvar

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