200-201 Network Intrusion Analysis Practice Question
A security analyst observes repeated ICMP port unreachable responses from a target host. The source IP is sending packets to multiple UDP ports. Which type of scan is most likely being performed?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
UDP scan
UDP scans elicit ICMP port unreachable messages from closed ports; open ports typically do not respond.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
TCP SYN scan
Why it's wrong here
TCP SYN scan uses TCP packets, not UDP.
- ✓
UDP scan
Why this is correct
UDP scan sends UDP datagrams; closed ports respond with ICMP port unreachable.
- ✗
TCP connect scan
Why it's wrong here
TCP connect scan completes full handshakes, not UDP.
- ✗
Ping sweep
Why it's wrong here
Ping sweep uses ICMP echo requests, not UDP probes.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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