Regarding the Wiki site OpenVPN server: Firewall configuration (using iptables), if the Pi-hole internal DHCP server is active, do we have to specify ports 67 (dnsmasq) and 68 (dhcpcd) too? Both are listening on 0.0.0.0. The above site only mentions ports 22, 53, 80, 1194.
Only 67 UDP is necessary for the DHCP service.
Port 68 is used when configured as a DHCP client (not static IP like Pi-hole).
Means the Wiki site has to be extended with information and further iptables rules regarding DHCP and port 67?
It is a Wiki.
A wiki (/ˈwɪki/ (About this sound listen) WIK-ee) is a website on which users collaboratively modify content and structure directly from the web browser.
This is no clear answer to my question.