Question
The rule "DHCP Client", that allows 68/tcp
(iptables) and 546/tcp
(ip6tables) appeared in the Plesk Firewall after Plesk 18.0.38, why?
Answer
The rule was added in order for the IPv6 addresses to be assigned properly via DHCP on the cloud-hosted servers.
Note: This rule can be safely disabled or altered at discretion in case the server doesn't use IPv6 via DHCP.