Which command initiates a UDP scan and targets UDP port 123?

• A. nmap -sT -p 123
• B. nmap -sN -p 123
• C. nmap -sU -p 123
• D. nmap -sA -p 123

Answer: (C)

UDP scanning in Nmap is requested with the -sU switch. This tells Nmap to use UDP, rather than TCP, for the probe. Pairing it with -p 123 directs the scan to UDP port 123. The other switches are for TCP-based scans (for example, a TCP connect scan, a TCP NULL/ACK scan), so they won’t perform a UDP scan. Therefore, combining -sU with -p 123 is the right approach to initiate a UDP scan on UDP port 123.