Setup Raspberry Pi3 as NTP server (not using external NTP server) - server

Question

I've searched around, but I cannot find an answer.
Can I use my Raspberry Pi as an NTP server (independently).
I want to synchronize 4 devices on a LAN for logging. They will be on a LAN with no WAN access... one is a Cisco Switch, one is the Pi and the other two are conversion boxes I want to log things on (they will be NTP client).
I just need them all to sysnc to 1 clock source (the Pi) is there a way to do this? All the answers I find are either to setup the Pi with a GPS module (which I can't do here) or sync it to external NTP servers for cascading the clock down (which I can't do here)... can I use NTP just to send out the Pi's system time ?

Answer 1

You could but best with a time source.
You would need to edit the code for a NTP server, as there isn't much cause to do this.
Best idea is to use a GPS hat on the RPi
http://www.reeve.com/Documents/Articles%20Papers/Reeve_GpsNtp-Pi.pdf

Answer 2

DEAR PEOPLE FROM THE FUTURE: Here's what we've figured out so far...
On your Raspberry Pi, run the following commands:
sudo apt update
sudo apt install ntp
sudo ufw allow ntp # if your firewall is enabled
sudo ufw allow 123
sudo sed --in-place --expression "\$aserver 127.127.1.0" /etc/ntp.conf
sudo systemctl start ntpd
On your Cisco switch, run the following commands:
NOTE - If you are using Cisco IOS, do not forget to force the NTP synchronization using clock read-calendar.
configure terminal
ntp server <the IPv4 address of your Raspberry Pi>
end
clock read-calendar
PS - If you want to shut everything down...
On your Raspberry Pi, run the following commands:
sudo ufw delete allow ntp
sudo ufw delete allow 123
sudo systemctl stop ntpd
sudo sed -i "/server 127.127.1.0/d" /etc/ntp.conf
On your Cisco switch, run the following commands:
configure terminal
no ntp server <the IPv4 address of your Raspberry Pi>
end