iptables:
add block:
sudo iptables -t nat -A PREROUTING -m mac --mac-source <MAC ADDRESS> -j DROP

remove block:
sudo iptables -t nat -D PREROUTING -m mac --mac-source <MAC ADDRESS> -j DROP

kernel null route:
add null route:
sudo route add -host <IP ADDRESS> reject

delete null route:
sudo route delete -host <IP ADDRESS> reject