What is the effect of the -n option in Nmap, and when would you disable DNS resolution?

• A. -n disables DNS resolution; disable when scanning many hosts or when DNS is slow or unnecessary.
• B. -n enables DNS resolution.
• C. -n changes network speed to fastest.
• D. -n toggles numeric hosts only.

Answer: (A)

Disabling DNS resolution is what the -n option does. Nmap normally tries to resolve hostnames to IP addresses (and may include hostnames in its output). By using -n, no DNS lookups are performed, so scans are driven strictly by the numeric addresses you provide and results show IPs only.

This is most useful when you’re scanning lots of hosts and DNS lookups would slow things down, or when DNS is slow or unreliable, or when you already have a list of IPs and don’t need hostnames in the results. If you need hostnames in the output, you wouldn’t use this option, and you would allow DNS resolution instead. Also, if you provide hostnames and use -n, those targets won’t be resolved to IPs, so the scan may not proceed as intended.