[ntp:questions] time delta between clients

Per Hedeland per at hedeland.org
Sun Dec 23 09:42:23 UTC 2007


In article <476DCB00.3090008 at alum.mit.edu> Tom Smith
<smith at alum.mit.edu> writes:
>Per Hedeland wrote:
>> In article <476B3C9C.8090607 at ntp.isc.org> mayer at ntp.isc.org (Danny
>> Mayer) writes:
>>> Per Hedeland wrote:
>>>> In article <4761F0AA.3060003 at cag.zko.hp.com> Tom Smith
>>>> <smith at cag.zko.hp.com> writes:
>>>>> Rick Jones wrote:
>>>>>> Rick Jones <rick.jones2 at hp.com> wrote:
>>>>>>> Here is what I have now that I've dropped the minpoll from the server
>>>>>>> and dropped LOCAL:
>>>>>>> peer bl480c2 minpoll 3 maxpoll 4 iburst
>>>>>>> server 10.208.0.1 iburst
>>>>>>> server 10.0.0.1
>>>>>>> server 10.202.1.1
>>>>>> Scratch that - I commented-out the last two servers.
>>>>>>
>>>>>> rick jones
>>>>> I think you may have problems, even in the mythical zero-latency network,
>>>>> getting the skew consistently below double the clock tick of the system
>>>>> with the largest clock tick interval.
>>>> Hm, if you were a newbie here, I'd assume that you simply don't know
>>>> what you're talking about, but since you aren't, I must be
>>>> misunderstanding you as you appear to be saying that two Unix hosts with
>>>> the traditional 100 Hz clock (on the same LAN) couldn't achieve a skew
>>>> consistently below 20 ms - while (at least) sub-millisecond offsets in
>>>> such setups are commonplace and discussed here every other day.
>>>> Apparently not even Windows has the kind of problem you suggest anymore.
>>>>
>>> While Rick may be a relative newbie to NTP he has had years of
>>> conducting performance analysis of applications and systems. His
>>> performance testing of BIND9 is probably *the* seminal reference on DNS
>>> testing.
>> 
>> Uh, your point being? I'm sure your description is correct even though I
>> have no knowledge of that subject (which doesn't seem to be relevant
>> here), and I specifically said that I *didn't* consider Rick a newbie to
>> NTP - based on the very limited knowledge of *that* subject that I have,
>> namely past postings in this forum. Which is why I found his statement
>> surprising, and assumed that I must be misunderstanding it. Are you
>> saying that you agree with that statement? Or maybe you can explain how
>> I'm misunderstanding it?
>
>Well, lets see if we can reduce the confusion a little. ;-)
>
>Rick (Jones) is the author of netperf. He deals with quite a large number
>of platforms, releases of those platforms, and combinations thereof.
>Tom (Smith) happens to work for the same company as Rick, also deals
>with quite a large number of platforms, releases, combinations, and with
>customers with large heterogeneous and problematic NTP networks, among
>other things.
>
>Per's question was to Tom's comment, not Rick's, and Tom's comment was to Rick,
>not Per. I imagine Rick may be just sitting on the sidelines scratching
>his head at this point wondering what he did wrong.

Thanks for that - I actually knew that I was responding to Tom
initially:-), and will blame Danny's message (which then seems even more
pointless) for making me mix up the names...:-) Now I'm just wondering
if Tom Smith at alum.mit.edu is the same person as Tom Smith at
cag.zko.hp.com?:-) Well, I guess I'm also still wondering whether the
latter is actually saying that it won't be possible to get the skew
below 20 ms with Unix hosts with 100Hz clocks, but it's not really
important - the important thing is that such a statement (if made) is
not correct.

--Per Hedeland
per at hedeland.org




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