Then, of course you would have to give more information to the community in order to get at least a suggestion.
Or, put a bunch of rules in the firewall, for each ip, something like: src-address=192.168.1.2 dst-address=192.168.1.0/24 action=drop.
Or like that. Extrapolate, and put a little effort.
Or, play with interfaces.
in-interface=local out-interface=local action=drop.
Your choice. Your network.