This is some test tools to test ntp servers.

Created: 2018-01-24

Software to ntp server stress test
Windows tool from Galleon:

Windows test tool - Aprox 64 packets / sec pr sesion - Local server

Windows test tool - Aprox 64 packets / sec pr sesion - from source

Linux tool by Kasper Pedersen

linux test tool - Aprox 4300 packets / sec pr RPI3 sesion- Local server - modified with argument by me
linux test tool - Aprox 4300 packets / sec pr RPI3 sesion- Local server - modified with argument by me - and compiled
linux test tool - Aprox 4300 packets / sec pr RPI3 sesion- Local server
linux test tool - Aprox 4300 packets / sec pr RPI3 sesion - from source

How to install linux tool

wget http://www.ntp.567.dk/software/ntpload3.c
gcc ntpload3.c -o ntpload3
# run it !!
./ntpload3 192.168.1.123

Here is my first stress test.
Server: RPI3 Linux raspberrypi 4.4.13-v7+ #894 SMP Mon Jun 13 13:13:27 BST 2016 armv7l GNU/Linux running ntpd 4.2.8p10@1.3728 First from 18:00 i tested with the windows tool, then at 19:30 - i found the linux tool
The test was runned from a Raspberry PI3 also -
1 sesion = 5.000 Packets/second
2 sesion =10.000 Packets/second
3 sesion =12.000 Packets/second
4 sesion =16.000 Packets/second
5 sesion =18.000 Packets/second

What is 5000 UDP Datagrams/s like ?

(Number of Packets per Second) x (Polling Rate) = Number of Clients

After an NTP client is synchronized, the default polling rate is 1024 seconds:
5000 packets/second x 1024 polling rate = 5.120.000 NTP clients

You can change the polling rate if you wish. Here is an example using 64 seconds:
5000 packets/second x 64 polling rate = 320.000 NTP clients