Re: [chrony-users] chronyc tracking question

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On Thu, Jul 27, 2017 at 4:57 AM, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
> 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.

Thanks for confirming.

> 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.

Doh.  Next time I'll try to read the man page more carefully.

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

I had come to the same realization a few hours after I had sent my prior email.

> 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.

Interesting thought.  I agree with your sentiment, "I'm not sure which
is worse."

> 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.

I had thought of the latter, but not the former.  I'll try both and
see how I make out.

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