Which technique involves sending a pre-connection SYN to probe a server before the full TCP handshake begins?

Which technique involves sending a pre-connection SYN to probe a server before the full TCP handshake begins?

• A. Session splicing
• B. Time to Live (TTL)
• C. ASCII shellcodes
• D. Pre-Connection SYN

Answer: (D)

This technique is the SYN scan approach. It sends a SYN packet to a target port to probe its state before the full TCP handshake is completed. In TCP, a connection would normally proceed with SYN, SYN-ACK, then ACK. A SYN scan uses only the initial SYN and then doesn’t finish the handshake—often sending a RST or simply leaving the connection half-open—so the scanner can determine whether a port is open, closed, or filtered based on the response. This allows port discovery with fewer resources and less chance of fully establishing a connection, which can be stealthier than a full three-way handshake. Other options describe different concepts (like TTL, shellcode, or unrelated session tricks) and don’t capture this probing method.

This technique is the SYN scan approach. It sends a SYN packet to a target port to probe its state before the full TCP handshake is completed. In TCP, a connection would normally proceed with SYN, SYN-ACK, then ACK. A SYN scan uses only the initial SYN and then doesn’t finish the handshake—often sending a RST or simply leaving the connection half-open—so the scanner can determine whether a port is open, closed, or filtered based on the response. This allows port discovery with fewer resources and less chance of fully establishing a connection, which can be stealthier than a full three-way handshake. Other options describe different concepts (like TTL, shellcode, or unrelated session tricks) and don’t capture this probing method.