Which of the following is an example of a firewall deny rule?

• A. add allow MAC 00:d0:59:aa:af:80 any in
• B. add deny ip from 10.121.70.151 to any in
• C. add deny mac 00:aa:bb:cc:dd:ee any in
• D. add allow ip from 0.0.0.0 to 255.255.255.255 in

Answer: (B)

A firewall deny rule works by blocking traffic that matches certain criteria. In this case, the rule blocks IP traffic coming into the network from a specific source address: the source IP is 10.121.70.151, destination is any, and it applies to inbound traffic. The action is deny, so any packet from that host trying to enter the network will be dropped. This is the classic, straightforward example of a deny rule: a precise match on IP and direction with a deny action.

The other options illustrate different ideas that aren’t the same as a standard IP-based deny rule. An allow rule lets traffic through, which is the opposite action. A deny by MAC address filters at the hardware or layer-2 level, which is a different filtering mechanism than the typical IP-based firewall rule. A broad allow rule would permit all traffic, which doesn’t demonstrate a deny action at all.