[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?

Often.
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.




More information about the questions mailing list