Может быть тут: /ip firewall filter
add chain=input connection-state=invalid action=drop \
comment="Drop Invalid connections"
add chain=input connection-state=established action=accept \
comment="Allow Established connections"
add chain=input protocol=icmp action=accept \
comment="Allow ICMP"
add chain=input src-address=
192.168.0.0/24 action=accept \
in-interface=!ether1
add chain=input action=drop comment="Drop everything else" ??