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

unruh unruh at wormhole.physics.ubc.ca
Mon May 31 21:10:57 UTC 2010

On 2010-05-31, Kalle Pokki <kalle.pokki at iki.fi> 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?

Misconfiguration, bad startup, ...

> What are the usual reasons for servers going crazy? From Mr. Mills'
> book I get the impression that he feels the NTP algorithms itself are
> stable. Using random internet servers is of course risky, as anyone
> could easily e.g. misconfigure a server to stratum 1 using only the
> LCL reference clock driver.

But the advice IS to use use random internet servers ( called the pool)

> If we assume there is a private subnet that has two GPS reference
> clocks to synchronize the rest of the machines, what would be the
> expected failure mode where one of the stratum 1 servers go crazy, and
> having three GPS clocks actually makes a difference?

The gps falls off the roof and is burried in shrub, but still uses its
internal clock to deliver PPS pulses is an example.

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