[ntp:questions] Synchronizing using servers in stratum 1 and 2

Timo Ruiter timo.ruiter at xs4all.nl
Wed Feb 14 18:25:06 UTC 2007

Timo Ruiter schreef:
> Hi all,
> When using pool.ntp.org the DNS randomly select time servers.  Since 
> stratum-1 servers and stratum-2 servers share the same pool you will get 
> a mix of them when using 0.nl.pool.ntp.org, 1.nl.pool.ntp.org, and 
> 2.nl.pool.ntp.org for instance.
> When you are assigned *one* stratum-1 server and *two* stratum-2 servers 
> your clock will obviously synchronize to the stratum-1 server. But that 
> being the case, what is the use of the two stratum-2 servers, assuming 
> that the stratum-1 server will not go off-line?
> Could it be so that if the stratum-1 server is not so accurate after all 
> it would still be selected over the stratum-2 servers (since no 
> reference stratum-1 server is available)?
> Will you not be better served instead when you are assigned *three* 
> stratum-2 servers, so the selection process of ntpd will compare all 
> three servers equally and choose the best one, switching to another if 
> that one looks more stable after a while?
> Regards,
> Timo
What I really wanted to know is what is better in terms of stability: 
*one* stratum-1 server and *two* stratum-2 servers versus *three* 
stratum-2 servers.
When having only one stratum-1 server available you might be relying on 
that server too much; when having three stratum-2 servers (ideally 
synchronized to three different stratum-1 servers) time *could* be more 
stable since there are three stratum-1 servers involved, albeit through 
the stratum-2 servers.

This is a pure theoretical issue as far as I'm concerned, since who can 
tell the difference if your servers are 23 milliseconds off...
So replace "stratum-1" by "stratum-N" and "stratum-2" by 
"stratum-(N-1)"; the question will remain the same.


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