This 200-201 practice question tests your understanding of network intrusion analysis. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security analyst observes a high volume of ICMP echo replies from multiple internal hosts to a single external IP address. Which type of network activity is most likely indicated?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Ping sweep
Ping sweep sends ICMP echo requests to multiple hosts to discover live hosts.
ARP spoofing
Why wrong: ARP spoofing involves falsified ARP messages to redirect traffic, not ICMP.
Port scan
Why wrong: Port scan typically uses TCP or UDP probes to discover open ports, not ICMP echo replies.
Smurf attack
Why wrong: Smurf attack is a DDoS that uses ICMP echo requests to broadcast addresses, not a sweep mapping hosts.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Ping sweep
A ping sweep uses ICMP echo requests to discover live hosts; the observed high volume of ICMP echo replies from multiple internal hosts to a single external IP indicates that the external IP sent a flood of echo requests, and the internal hosts are responding. This is the classic signature of a ping sweep (or ICMP sweep) where an attacker probes a range of internal addresses to map the network.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Ping sweep
Why this is correct
Ping sweep sends ICMP echo requests to multiple hosts to discover live hosts.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
ARP spoofing
Port scan
Smurf attack
Why it's wrong here
Smurf attack is a DDoS that uses ICMP echo requests to broadcast addresses, not a sweep mapping hosts.
Common exam traps
Cisco often tests the distinction between a Smurf attack and a ping sweep by emphasizing that in a Smurf attack the replies are directed to a spoofed victim IP (often internal), whereas here the replies go to a single external IP, making it a sweep.
Detailed technical explanation
Under the hood, a ping sweep often uses a tool like fping or nmap with the -sn flag to send ICMP echo requests to a subnet; the replies are collected to build a host list. In real-world scenarios, attackers may combine ping sweeps with TCP SYN scans to avoid detection by firewalls that block ICMP, but a pure ICMP echo reply flood from multiple internal hosts to one external IP is a strong indicator of an external host performing a sweep.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Network Intrusion Analysis — This question tests Network Intrusion Analysis — Read the scenario before looking for a memorised answer..
The correct answer is: Ping sweep — A ping sweep uses ICMP echo requests to discover live hosts; the observed high volume of ICMP echo replies from multiple internal hosts to a single external IP indicates that the external IP sent a flood of echo requests, and the internal hosts are responding. This is the classic signature of a ping sweep (or ICMP sweep) where an attacker probes a range of internal addresses to map the network.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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