[ntp:questions] Very rapid polling

Danny Mayer mayer at ntp.org
Sun Feb 15 20:00:47 UTC 2009


gary.limanapier at elisys.co.uk wrote:
> On Feb 15, 9:15 am, Uwe Klein <uwe_klein_habertw... at t-online.de>
> wrote:
>> gary.limanap... at elisys.co.uk wrote:
>>> Just joining this discussion as we have noticed NTP request from our
>>> Authorised Server every 300ms on our LAN. They occur only between the
>>> Time Server and the WiFi Tablet during a socket connection while there
>>> is a low signal strength. The Tablet sends its own NTP request with a
>>> Poll Interval of 4 (16 seconds). The server returns its response
>>> increasing the Poll Interval to 10 (1024 secs). The server then keeps
>>> sending this same packet every 300-500ms.
>> Does the ntp process submit these packets repeatedly or
>> are you seeing some (uncalled for) "collision/resend" action due to
>> issues with the wlan connection?
>>
>> uwe
> 
> Would it matter if the packet colided? NTP is using UDP and I can't
> see from the packet analyser that it is expects a response back. When
> it does work with a known good machine there is no acknowledgement of
> the packet being sent. Do you think that there another level of
> operation in the network that I am not seeing with the packet analyser?

How would an NTP packet collide? With what? NTP packets are always
unique. If a client sends a packet to the server it will get a response
(if it responds at all) with an identical-looking packet. If there is no
response either the server is dropping the request or there is a
firewall in the way dropping the requests. This is not an ethernet
packet and the nature of UDP is that there is no automatic resend.

Danny



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