Port specification and scan order

• Single port: For example, -p 21
• The range of ports (from 1 to 1,000): For example, -p 1-1000
• A list of ports: For example, -p 21, 25, 80
• Popular ports: --top-ports [number] (for example, --top-ports 100 or --top-ports 1000)
• Scan fewer ports than the scanner default port numbers (fast mode): -F