[ntp:questions] General ntp architecture question

Richard B. Gilbert rgilbert88 at comcast.net
Mon Aug 2 12:40:23 UTC 2010

konsu wrote:
> Hello list,
> I work for an investment bank with 300 UNIX servers, around 3000
> workstation PCs and would like to ask some questions to more
> experience users.
> a) Are there any banks relying on ntp pool project or should we
> consider having our own GPS clock ?

Ask a banker.  For most of us the question is out of our area of expertise!

> b) What are the criteria to consider in deciding when ntp pool project
> is enough for our needs ?

1. Availability
2. Reliability
3. Distance from your site.  Absurd example: If you are in New York 
City, you would NOT want to configure a server in Tokyo!

> c) Should we decide to use ntp, for an organization of our size would
> 2 servers syncing to ntp pool project in DMZ and 2 servers inside to
> which all UNIX servers + Domain Controller will sync (PCs would sync
> to the Domain controller) suffice ?

I would suggest that you consider purchasing a GPS Timing Receiver and 
installing it.  If you can site an antenna smaller than a hockey puck 
somewhere within reach and with a good view of the sky, and connect it 
to your receiver and your receiver to your computer you will have your 
very own Stratum 1 server.  You also minimize your exposure to other 
people's mistakes and disasters.

Don't use two servers!  It is written that a man with two clocks can 
never be certain what time it is.  Four servers is generally regarded as 
the minimum.  A configuration of five servers can survive the failure of 
two servers and a configuration of seven servers is able to survive the 
failure of three.

Failure, in this context, can mean either not responding or responding 
with an incorrect time.  The last NTP survey found one server that 
responded with the wrong year!!  This sort of thing does not happen 
often; that survey covered several thousand NTP servers and most of the 

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