In firewall terminology, which action notifies the source when blocking a packet?

• A. Allow: allow packet to pass
• B. Drop: drops the packet without any diagnostic message to the packet source host
• C. Deny: Do not let the packet pass, but notify the source host
• D. Reject: send an ICMP error to the sender

Answer: (C)

The action being tested is how a firewall handles blocked traffic and whether it informs the sender. Notifying the source when blocking means the firewall stops the packet and sends some form of response back to the originator to indicate it was blocked. That behavior is described by the deny action: it does not let the packet pass, but it informs the source host. In practice, the notification could be an ICMP message or another diagnostic signal, depending on the device and configuration.

Dropping would discard the packet silently, with no notification. Allowing would let the traffic through. Rejecting would send a specific error back to the sender (an explicit ICMP error or reset), which is a different kind of notification than the deny action described here.