During an external penetration test, you need to discover which TCP services a remote server exposes, but you must avoid completing the full three-way handshake so that service daemons generate as few log entries as possible. Which Nmap scan type should you choose?
The TCP SYN scan (-sS) sends only the initial SYN packet and interprets the reply, never completing the handshake. Because no ACK is returned, most daemons do not register the connection in their application-level logs, making the technique stealthier than a full TCP connect scan. A TCP connect scan (-sT) finishes the handshake and is therefore noisier. An ACK scan (-sA) is used primarily for firewall rule discovery, not for identifying open ports, and a UDP scan (-sU) targets UDP services, not TCP.
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What is the three-way handshake in TCP?
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Why is a TCP SYN scan (-sS) considered stealthier?
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When would you use an ACK scan (-sA) instead of a SYN scan?
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Why is a TCP SYN scan (-sS) considered stealthy?
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What is the purpose of the TCP ACK scan (-sA)?
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How does a UDP discovery scan (-sU) differ from TCP scans?
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Reconnaissance Techniques
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