Which scan type establishes a full three-way handshake (TCP Connect Scan)?

Which scan type establishes a full three-way handshake (TCP Connect Scan)?

• A. -sT
• B. -sO
• C. -sP
• D. -sR

Answer: (A)

The scan type that establishes a full three-way handshake is the TCP connect approach. It uses the system’s connect() call to try to open a real TCP connection to the target port, which means the full handshake—SYN, SYN-ACK, and ACK—occurs. If the port is open, the handshake completes and the connection is established (and then typically torn down by the scanner). This provides definitive evidence that the port is open, but it’s noisier and more easily detected because it completes a full TCP connection. The other options don’t perform a standard TCP handshake: the IP protocol scan sends crafted IP packets to detect which IP protocols the host supports; the ping sweep simply checks if a host is up; the RPC scan targets remote procedure call services and asks about RPC-specific ports rather than establishing a general TCP connection.

The scan type that establishes a full three-way handshake is the TCP connect approach. It uses the system’s connect() call to try to open a real TCP connection to the target port, which means the full handshake—SYN, SYN-ACK, and ACK—occurs. If the port is open, the handshake completes and the connection is established (and then typically torn down by the scanner). This provides definitive evidence that the port is open, but it’s noisier and more easily detected because it completes a full TCP connection.

The other options don’t perform a standard TCP handshake: the IP protocol scan sends crafted IP packets to detect which IP protocols the host supports; the ping sweep simply checks if a host is up; the RPC scan targets remote procedure call services and asks about RPC-specific ports rather than establishing a general TCP connection.