Which is the correct syntax to scan ports in a range from 1 to 20?

• A. -p 1-20
• B. -p 0-20
• C. -p 1-21
• D. -p 2-20

Answer: (A)

To scan a specific port range in Nmap, you use the -p option followed by a start-end range, and both ends are inclusive. Scanning ports 1 through 20 is done with -p 1-20. Port numbers start at 1; 0 is not a valid port, so -p 0-20 would be inappropriate. Including 21 would extend the range beyond the requested upper bound, and starting at 2 would miss port 1. In general, valid ports go from 1 to 65535, so -p 1-20 correctly targets exactly the first twenty ports.