Which statement best describes UDP scanning relative to TCP scanning?

Which statement best describes UDP scanning relative to TCP scanning?

• A. -sT
• B. Generally slower and more difficult than TCP scanning
• C. Open Response: A service responds with a UDP packet
• D. Filtered Response: Other ICMP unreachable errors (type 3, codes 0, 1, 2, 9, 10, 13)

Answer: (B)

UDP scanning is slower and more difficult than TCP scanning because UDP is a connectionless protocol with no guaranteed reply. When you probe UDP ports, many open ports don’t respond at all, and whether a port is closed may only be inferred from ICMP unreachable messages or from no response at all, which makes it hard to draw firm conclusions. Firewalls and rate-limiting commonly drop UDP traffic, so you often have to send many probes and wait longer to obtain meaningful results. In contrast, TCP scanning benefits from clearer state indicators (open ports often reply with a connection-backed response, while closed ports typically respond with a reset), making results faster and more straightforward to interpret. The other statements describe specific scan switches or particular response types, which don’t capture the general challenge posed by UDP scanning.

UDP scanning is slower and more difficult than TCP scanning because UDP is a connectionless protocol with no guaranteed reply. When you probe UDP ports, many open ports don’t respond at all, and whether a port is closed may only be inferred from ICMP unreachable messages or from no response at all, which makes it hard to draw firm conclusions. Firewalls and rate-limiting commonly drop UDP traffic, so you often have to send many probes and wait longer to obtain meaningful results. In contrast, TCP scanning benefits from clearer state indicators (open ports often reply with a connection-backed response, while closed ports typically respond with a reset), making results faster and more straightforward to interpret. The other statements describe specific scan switches or particular response types, which don’t capture the general challenge posed by UDP scanning.