[ntp:questions] How to get a list of > 500 ntp clients

Kiss Gábor kissg at niif.hu
Tue Aug 13 18:18:56 UTC 2019

> I?m running NTP servers on centos 7.6. I know that I can get a list of ntp clients doing ?ntpq -p? but I seem to remember reading somewhere that it was limited to 500 clients.
> Is there another method in which I can quickly get / monitor the number of clients that are ?attached? to my server if I plan on having a few thousand clients?

You can set up an 'ip set' in your packet filter subsystem.
A firewall rule listens incoming packets and if destination port is UDP 123
then it adds the source address to the set.
You can configure a default expiry time (e.g. 3600 seconds) for the ip set.
After this time entries will wiped out unless another incoming packet
from the same address arrives.
So each time you list the content of the set you can see the
clients of the past hour.



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