[ntp:questions] Re: Question on abusive clients.

David L. Mills mills at udel.edu
Fri Dec 23 01:35:56 UTC 2005


There are copious examples of that happening right now on the NIST and 
USNO servers. What would you suggest we do to stop it? See the paper

Mills, D.L., J. Levine, R. Schmidt and D. Plonka. Coping with overload 
on the Network Time Protocol public servers. Proc. Precision Time and 
Time Interval (PTTI) Applications and Planning Meeting (Washington DC, 
December 2004), 5-16.

Full text is at www.eecis.udel.edu/~mills/papers.html.


David J Taylor wrote:
> [Excuse top-post]
> .. and so if the client ignores the KoD, it may keep hammering on the 
> server every second?
> David
> David L. Mills wrote:
>>Current ntpd will clamp the poll interval to not less than 4 in server
>>replies no matter what the client says. If KoD is enabled, it will
>>return KoD packets if the headway beteen packets is less than 1 s or
>>the average headway is less than 4 s.
>>David J Taylor wrote:
>>>On a related topic, what does NTP do if a request is received with
>>>the Poll field set to less than the minimum value (4)?  Is the
>>>request silently dropped?  Or a KOD packet sent?

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