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

Blair Zajac blair at orcaware.com
Wed Apr 10 02:07:39 UTC 2013


Thanks Charles,

OK.  So unless I go for some GPS-based clocks in my servers, each data 
center will use close stratum-2 servers and the stratum-3 clocks will 
not peer with clocks in my other datacenters.

Regarding peering, then 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 [1] suggests they should be 
split?   If that's the case, then how are falsetickers identified?

Blair

[1] http://www.ntp.org/ntpfaq/NTP-s-config-adv.htm#AEN3101

On 04/08/2013 05:45 PM, Charles Elliott wrote:
> I don't think you will ever achieve acceptable synchronization between the
> data centers without accurate external clocks, such as GPS-based clocks,
> attached to a time server in each location.  Internet traffic acts as waves
> of high use and periods of quiescence.  During these periods of high traffic
> your data centers will differ by 250 ms or more and will take some time to
> resynchronize during quiescent periods.  This problem is greatly exacerbated
> by the large distances between your data center locations.  NTPD cannot
> prevent that.  Nor is it really NTPD's fault.  The ISPs have installed very
> large buffers in front of their routers to prevent dropping packets and
> sending choke packets to the data originators, as the Internet was
> originally designed.  Hence the Internet is not automatically rerouting
> packets when traffic patterns change, again as originally designed.  Money
> is the root of all evil.
>
> Charles Elliott
>
>> -----Original Message-----
>> From: questions-bounces+elliott.ch=verizon.net at lists.ntp.org
>> [mailto:questions-bounces+elliott.ch=verizon.net at lists.ntp.org] On
>> Behalf Of Blair Zajac
>> Sent: Saturday, April 6, 2013 9:01 PM
>> To: questions at lists.ntp.org
>> Subject: [ntp:questions] Syncing and peering for a multi-continent
>> deployment
>>
>> 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.
>>
>> Questions:
>>
>> 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
>> clocks?
>>
>> 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.
>>
>> Thanks,
>> Blair
>>
>> [1]
>> http://support.ntp.org/bin/view/Support/SelectingOffsiteNTPServers#Sect
>> i
>> [2]
>> http://support.ntp.org/bin/view/Support/SelectingOffsiteNTPServers#Sect
>> i
>> [3]
>> http://support.ntp.org/bin/view/Support/StartingNTP4#Section_7.1.4.3.2.
>> [4] http://www.ntp.org/ntpfaq/NTP-s-config-adv.htm#AEN3101
>> _______________________________________________
>> questions mailing list
>> questions at lists.ntp.org
>> http://lists.ntp.org/listinfo/questions
>



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