...

If everything works well you should see first Cable Modems requesting DHCP (DISCOVER, OFFER, REQUEST, ACK) followed by Named and tftp config file download

DNS

Check if we you can resolve cable modem hostnames hostname via ping, like

ping cm-100000.nmsprime.test
# NOTE: ping must be working!

If this is not working then add the following line to you /etc/sysconfig/network-scripts/ifcfg-... public interface file:

...

systemctl restart network

Then check the /etc/resolv.conf file. There should be NO hostname statement with an external DNS IP inside of it.