What is the response from an open UDP port which is not behind a firewall?

UDP’s connectionless nature means it lacks inherent acknowledgment mechanisms, affecting its port response behavior.

Why B is correct:An open UDP port does not respond unless an application explicitly sends a reply. Without a firewall or application response, the sender receives no feedback, per CNSP scanning guidelines.

Why other options are incorrect:

A:ICMP Port Unreachable indicates a closed port, not an open one.

C:SYN packets are TCP-specific, not UDP.

D:FIN packets are also TCP-specific.

References:CNSP "UDP Scanning" (Section on Port Behavior) notes "no response" as the default for open UDP ports.