[ntp:questions] Re: NTP Server abuse

Brad Knowles brad at stop.mail-abuse.org
Wed Dec 1 10:09:53 UTC 2004


At 9:50 PM -0500 2004-11-30, Danny Mayer wrote:

>  To accomplish that, you first to define what is an abuser.

	In this case, it's actually pretty easy to do that.  Barring 
short startup periods, an abuser is anyone who makes more than one 
query roughly every 1024 seconds.  You might want to be generous and 
allow them to make queries as frequently as every 512 or 256 seconds.

	I think that this much has already been done, and simple 
prototype scripts have already been developed for some OSes to detect 
excessive traffic and to automatically generate firewall rules to 
send that somewhere else.

>  What may be better is to use SRV records instead (along with the
>  programming involved), so that only those developers keeping up
>  with the standards get to find out what's in the pool.

	It's all well and good to say this, but ntpd doesn't support SRV, does it?

	What do we do for all the old NTP clients (such as our own 
ntpd-4.2.0) that don't support SRV?

	How many years would be a reasonable time to wait for all 
"reasonable" clients to update to an SRV-aware implementation?

	Until that time comes along, what do we do -- just shut down 
pool.ntp.org altogether?

>  One idea I had was for a non-authorized client to be returned a
>  KOD and a timestamp to indicate that their clock was too
>  fast and keep moving it further and further back. A properly written
>  ntp app would notice quickly that it was getting a KOD and ignore
>  the bad time and quickly prefer a different server. A badly written
>  one would merrily accept the timestamp anyway and finding itself
>  further and further away from the accurate time. After a while any
>  use would notice how far off it was and switch to a different server.

	That's a nice idea.  When could we expect that to be tested, 
working, and in the field?

	In the meanwhile, do you have any suggestions for what we could 
do with the code as it exists today?

-- 
Brad Knowles, <brad at stop.mail-abuse.org>

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."

     -- Benjamin Franklin (1706-1790), reply of the Pennsylvania
     Assembly to the Governor, November 11, 1755

   SAGE member since 1995.  See <http://www.sage.org/> for more info.



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