4 is better than 3 because from time to time, one of them will be
unreachable. If one uses 3 and this happens, there is nobody to break a
tie.
I recommend also having these top-tier time sources 'peer' with each other.
What is your "interesting" issue with leap seconds?
H
On 4/8/2023 7:49 AM, MAYER Hans wrote:
Dear All,
I would say 3 ntp servers are also fine and good enough as there are never
taken more than 3 servers.
If there are no stratum-1 server available I would define at least 4 pools for
these 3 NTP servers.
I can tell you what I have done. Without claim to be correct.
I have 3 stratum-1 server ( GPS, DCF77 and rubidium disciplined )
The GPS and DCF77 are peered with the same type of server with another
organisation. In case the stratum-0 source would fail.
Below this I have 4 stratum-2 server which have also upstream servers from the
Internet. Just in case all 3 internal stratum-1 would fail.
There I am using two different types of daemon software. And 3 of these 4
servers are public available as part of the AT-pool (Austrian) for IPv6.
And internally I use only 2 stratum-3 servers for all clients. Good enough as I
manage and monitor complete NTP infrastructure.
These stratum-3 servers have defined all 4 of my stratum-2 servers I have and
are not using any external time source.
In my opinion it is not important to be accurate within a millisecond to the
real time. It is more important that all devices have the same time.
This becomes interesting especially if there is a leap second.
Therefore all clients are not allowed to fetch the time from Internet and such
traffic is prohibited by firewall.
To avoid that mis-configured clients have NO time I am using RPZ ( restricted
policy zones ) in DNS where a lot of well known DNS names for NTP servers are
rewritten to the internal IP address.
Kind regards
Hans
—
On 08.04.2023, at 13:37, Terje Mathisen <[email protected]> wrote:
Renzo Marengo wrote:
Il giorno venerdì 7 aprile 2023 alle 13:44:59 UTC+2 David Woolley ha
scritto:
On 07/04/2023 10:47, Renzo Marengo wrote:
I know NTP server numbers must be 1, 3 or 4,....
I don't understand this. NTP servers don't have numbers. They do
have a stratum, but that is determined automatically from the
current time distribution tree.
I wanted to say... the number (quantity) of ntp server. Now I have 3
ntp server(NTP1, NTP2, NTP3), if I had had 2 servers it should be
always a good idea ? I remembered there was a reason to have a
similar quantity (that is 3)
Server A has stratum 2 Server NTP1, NTP2, NTP3 has stratum 3
What do you think if I destroyed the Server A and I converted the
NTP1, NTP2, NTP3 to stratum 2 ? I would link these 3 server to the to
same time source of server A.
Your clients should all have at least 4 sources, so if you don't want them to
talk to the outside world, that means having at least that many internal
servers for them to reference.
Terje
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