Vinicius Cordeiro

Para bloquear:

sudo iptables -t filter -A FORWARD -d 0/0 -s IP -m mac –mac-source MAC_ADDRESS -j REJECT

Para liberar:

sudo iptables -t filter -D FORWARD -d 0/0 -s IP -m mac –mac-source MAC_ADDRESS -j ACCEPT

Bastando mudar IP e MAC_ADDRESS.