Redundant DHCP server and DNS Resolver using OpenBSD and FreeBSD

Some time ago, I set up Redundant DHCP server and DNS Resolver using OpenBSD . Time has past and one of the Raspberry Pi board I own is now running FreeBSD while the ODROID HC4 is running OpenBSD . I secured both my DHCP server and DNS resolver services running on those boards so that I can perform maintenance on one machine without turning down the whole services set.