On FreeBSD the SSHd root login is disabled by default. Now to allow root login only for a specific network range or network host add the following to /etc/ssh/sshd_config:

Match Address 192.168.0.*, 172.16.0.1, 172.16.0.2, 172.16.*.*
        PermitRootLogin yes

the addresses are separated by commas and i guess the asterisk is self-explaining if you are into computing 😛