In this video, I'll tell you a bit about managing an NTP server.
Internet time services have a reliability, and this reliability is expressed as a stratum.
Stratum-1 servers have the highest level of reliability.
Typically they are atomic clocks, very accurate.
And if a time synchronization process synchronizes with the stratum-1 server, itself becomes
a stratum-2 server.
If the firewall allows access to NTP port 123, it makes an NTP client that successfully
synchronizes an NTP server as well.
Now in your NTP server, you can also set stratum-10.
Stratum-10 is commonly used as a backup configuration.
So the stratum is low enough, which makes it unlikely that any NTP client ever synchronizes
with it.
But if the internet goes down, then you still have your local time synchronization and time-dependent
applications within your network keep on functioning.
So stratum-16 can also be used.
That is what you use to advertise the unavailability of an NTP service.
So what do we need to make sure that our Crony-D server is really an NTP server?
Well, very easy.
Just open the port in the firewall.
You will learn in a later lesson how to do so.