[ntp:questions] what happens when sys.peer turns stratum 16?

Richard B. Gilbert rgilbert88 at comcast.net
Mon May 31 19:14:28 UTC 2010

Kalle Pokki wrote:
> On Mon, May 31, 2010 at 06:42, unruh <unruh at wormhole.physics.ubc.ca> wrote:
>> Note, that this is one of the reasons why your customers should never
>> use 2 servers. You have no way to know which one is crazy. Use 3 or 5.
>> (4 can be as bad as 2 if two of the servers go nuts in exactly the same
>> way-- eg they are both tied to a single server which has gone nuts).
> The concept of configuring lots of servers in case some of them go
> crazy comes up often in the mailing list. Is this really a common
> problem with NTP? How often are there really crazy servers whose time
> is off by more than milliseconds?

The last NTP survey turned up one system that was responding with the 
wrong year!

The more common case is that a server fails due to something like a 
power outrage.  When the power comes back, that server may be off by 
several seconds, or minutes.  It may take ten to twelve hours before 
that server is fit to serve time to any but the truly desperate!

> What are the usual reasons for servers going crazy? 

A power outrage is the most likely cause.  If the power is off long 
enough for the UPS to run down it will probably take ten to twelve hours 
to stabilize with the correct time.

The next most likely is human tinkering.  Then there are the people who 
think that a time server can be started at 8:30 AM and shut down at 5:00 
PM Monday through Friday and still do a decent job of serving time!


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