[ntp:questions] ntp architecture

Marco Marongiu brontolinux at gmail.com
Tue May 21 14:18:24 UTC 2013

On 21/05/2013 14:31, Riccardo Castellani wrote:
> n.4 srv Internet--> server A
> server A --> server B
> server 
> A --> server C
> A is my internal source
> B,C are cluster machine so hardware 
> is reliable but I don't want to present these servers directly  on pubblic 
> network

My comments:

1) two servers is maybe the worst situation; use one, or three, or four
if possible, but not two.
See http://www.ntp.org/ntpfaq/NTP-s-algo-real.htm#Q-NTP-ALGO

2) both servers pointing to A: A is a single point of failure. If A
dies, B and C will both be left to their own devices.

I had a similar problem -- I needed to feed clients in a private network
that were not NAT'ed to the public network, and did as follows.

I have four servers on the public network, Pu1..Pu4; each of those
server uses four different public sources, and no public source is
shared between two different servers (so they are 16 in total).

I have four servers on the private network, Pr1..Pr4. Each one of them
uses Pu1..Pu4 as sources, but PrX marks PuX as preferred. This way, in
normal conditions they all follow a separate source (in a sense, PrX is
a "repeater" of PuX in the private network).

If a public servers fails, say Pu1, then Pr1 will follow the one among
Pu2..Pu4 it thinks it's the best. The service on both public and private
will be a bit degraded, but the resulting configuration will still be
good enough to give us time to fix problems safely.


-- bronto

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