unruh <un...@wormhole.physics.ubc.ca> writes:
> On 2011-02-08, Chuck Swiger <cswi...@mac.com> wrote:
>> On Feb 8, 2011, at 12:05 PM, Richard B. Gilbert wrote:
>>>>> What would wild swings in latency on the order of seconds from a
>>>>> ntp client register on a ntp server as?
>>>>
>>>> High latency ("delay" column in "ntpq -p" output), high jitter.
>>>>
>>>> Regards,
>>>
>>> Why would the server even notice what the client is doing? The
>>> server does not monitor clients, it simply responds with the correct
>>> time whenever it is asked for the correct time.
>>>
>>> Now ntpq -p on the *client* would show "High latency", etc.
>>
>> I agree that "ntpq -p" on the client should show this; that was what
>> I'd meant to suggest. :-)
>>
>> This being said, a NTP client does indeed provide it's time to the
>> server when making an NTP request, in a field called the "Transmit
>> Timestamp". A typical NTP exchange looks like the following:
>
> Yes, but all the server does is to copy that timestamp into the
> outgoing packet, puts its received timestamp into the appropriate box
> and when it is ready to send the packet pack, put in its own transmit
> timestamp
Presently! It sounds like a lightly modified ntp server - or set thereof
- could actually attempt to keep track of this information. Might even
be possible to do it in a pf or iptables rule.
>> # tcpdump -n -s 0 -v -v port ntp
[Elided]
Do ntp clients use an ephemeral udp src address for a query?
--
Dave Taht
http://nex-6.taht.net
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