[ntp:questions] Syncing and peering for a multi-continent deployment

Blair Zajac blair at orcaware.com
Sun Apr 7 01:01:29 UTC 2013

I'm working on deploying a large number of servers to data centers on 
three continents, say US, Europe and India.  Because each data center 
will be writing data and timestamping the data, I want them all to think 
they are at the same time, even if it isn't exactly the correct UTC 
time.  The data will be synced to other data centers, so relative 
ordering of when something happened can be important.

To not ping stratum-1 and -2 level servers from a large number of boxes, 
I'm setting up three stratum-3 NTP servers in each data center.

Here's what I've read:

1) Each ntp server should have 4 to 7 upstream clocks [1], [2], [3].

2) The three stratum-3 NTP servers in each data center should be peers 
of each other [4].  So each NTP server would have at most 2+7=9 connections.


1) Should each data center use nearby stratum-2 clocks or pick a set of 
stratum-2 clocks that are network wise in the center between all data 
centers (it may not be possible to get a true center)?

2) Should each stratum-3 server in a single data center use all 4-7 
upstream clocks?  Or should the 4-7 be split between the three stratum-3 
servers?  The diagram at [4] suggests they should be split?  If that's 
the case, then how are falsetickers identified?

3) Should I have all the stratum-3 servers in each data center be peers 
of each other, so each would have 8 peers?  This would ensure that all 
my clocks think they are at the same time.  If I do this, then I would 
need to increase maxclocks to support up to 7 (upstream) + 8 (peers)=15 

4) Or, should I not peer data centers to each other and trust that the 
stratum-2 clocks near each data center will be close to the other clocks?

Other random questions:

1) It doesn't appear that its necessary to set up symmetric keys for peers?

2) Is there a way to tell which peer is the "master" peer?  Looking 
through ntpdc and ntpq I didn't see anything.


[1] http://support.ntp.org/bin/view/Support/SelectingOffsiteNTPServers#Secti
[2] http://support.ntp.org/bin/view/Support/SelectingOffsiteNTPServers#Secti
[3] http://support.ntp.org/bin/view/Support/StartingNTP4#Section_7.
[4] http://www.ntp.org/ntpfaq/NTP-s-config-adv.htm#AEN3101

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