200-201 Network Intrusion Analysis Practice Question
An analyst is analyzing a PCAP and sees multiple ICMP port unreachable responses from a target host when scanning UDP ports. What does this indicate about the scanned ports?
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
✓
The ports are closed.
When a UDP scan sends a packet to a closed port, the target responds with an ICMP port unreachable message.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The ports are closed.
Why this is correct
Correct. ICMP port unreachable indicates closed port.
- ✗
The scan is a SYN scan.
Why it's wrong here
SYN scan uses TCP, not UDP.
- ✗
The ports are filtered by a firewall.
Why it's wrong here
Filtered ports may drop packets without response.
- ✗
The ports are open.
Why it's wrong here
Open UDP ports do not send ICMP unreachable.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-201 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 200-201 exam.