Which option performs a TCP connect scan?

Which option performs a TCP connect scan?

• A. -sN
• B. -sL
• C. -sX
• D. -sT

Answer: (D)

The method tests port state by using the operating system’s normal TCP connection process to complete a full handshake with the target. This is a TCP connect scan, where the scanner attempts to establish a real TCP connection to each port via the system’s connect() call. If the port is open, the handshake finishes and the scanner immediately closes the connection, marking the port as open. If the port is closed, the connect attempt fails quickly with a connection refusal, marking it as closed. If filtering or a firewall blocks the attempt, there may be no response, leading to a timeout or other filtering indication. This contrasts with the other techniques, which don’t establish a full connection: those send packets with unusual flag combinations or no flags to infer state without completing a handshake, or simply list targets without scanning ports.

The method tests port state by using the operating system’s normal TCP connection process to complete a full handshake with the target. This is a TCP connect scan, where the scanner attempts to establish a real TCP connection to each port via the system’s connect() call. If the port is open, the handshake finishes and the scanner immediately closes the connection, marking the port as open. If the port is closed, the connect attempt fails quickly with a connection refusal, marking it as closed. If filtering or a firewall blocks the attempt, there may be no response, leading to a timeout or other filtering indication. This contrasts with the other techniques, which don’t establish a full connection: those send packets with unusual flag combinations or no flags to infer state without completing a handshake, or simply list targets without scanning ports.