Which NetCat option enables zero-I/O mode, where no data is sent or received?

• A. -z
• B. -w
• C. -L
• D. -n

Answer: (A)

This question tests understanding of NetCat’s zero-I/O mode, which is used to scan ports without sending or receiving any data. The flag that enables this behavior is the -z option. When you use it (often with -v to show results) NetCat will try to connect to each target port and then immediately stop transmitting or receiving payload, reporting whether the port is open or closed. No data is sent and nothing is read after the connection is established, making it ideal for quick port discovery.

Other options have different purposes: -w sets a timeout for connection attempts and final reads, but it doesn’t imply zero I/O; -L switches NetCat into a re-listen mode, acting like a server to accept new connections; -n tells NetCat not to resolve hostnames via DNS, using numeric addresses only. None of these implement the zero-I/O scanning behavior.