The correct first step for host discovery in a penetration test is a ping sweep using ICMP echo requests. This technique is ideal because ICMP Type 8 packets are a standard, low-overhead method that quickly identifies live hosts without initiating full protocol handshakes or service interactions, thereby minimizing network disruption and the risk of triggering intrusion detection systems. On the CISSP exam, this question tests your understanding of the penetration testing methodology, specifically the principle of starting with passive or low-impact reconnaissance before escalating to more intrusive techniques. A common trap is choosing a more aggressive scan like a TCP SYN scan, which is reserved for later stages after live hosts are confirmed. Remember the memory tip: “Ping first, probe later”—ICMP is your quiet knock on the door before you try the handle.
CISSP Security Assessment and Testing Practice Question
This CISSP practice question tests your understanding of security assessment and testing. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 assessor is conducting a penetration test and needs to identify live hosts on a network without causing disruption. Which of the following techniques should the assessor use FIRST?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Ping sweep using ICMP echo requests.
A ping sweep using ICMP echo requests (ICMP Type 8) is the most appropriate first step for identifying live hosts on a network because it is a standard, low-disruption method that quickly determines host availability. ICMP echo requests are typically allowed by default on many networks and do not initiate full protocol handshakes or service interactions, minimizing the risk of triggering alarms or causing instability. This aligns with the penetration testing methodology of starting with passive or low-impact reconnaissance before escalating to more intrusive techniques.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
ARP scan to discover hosts on the local subnet.
Why it's wrong here
ARP scan is limited to the local subnet and may not reach all targets.
✓
Ping sweep using ICMP echo requests.
Why this is correct
Ping sweep is a standard, non-disruptive host discovery technique.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Vulnerability scan of all IP addresses in the target range.
Why it's wrong here
Vulnerability scanning is typically performed after identifying live hosts.
✗
Full TCP port scan on common ports.
Why it's wrong here
Port scan is more intrusive and should be done after host discovery.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose 'ARP scan' (Option A) thinking it is the least disruptive, but they forget that ARP is limited to the local broadcast domain and cannot discover hosts across routers, making it ineffective for a penetration test that typically spans multiple subnets.
Detailed technical explanation
How to think about this question
ICMP echo requests (ping) operate at the network layer (Layer 3) and do not require a transport-layer connection, making them lightweight and less likely to be blocked by host-based firewalls that permit ICMP but restrict TCP/UDP. However, many modern networks block ICMP echo requests for security reasons, so a penetration tester might follow up with a TCP SYN ping (e.g., to port 80 or 443) as an alternative, but the question specifies 'without causing disruption,' and ICMP remains the least disruptive standard option. In real-world scenarios, using a tool like `nmap -sn` (ping sweep) with multiple techniques (ICMP, TCP SYN, ARP) can increase accuracy while still being relatively low-impact.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Security Assessment and Testing — This question tests Security Assessment and Testing — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Ping sweep using ICMP echo requests. — A ping sweep using ICMP echo requests (ICMP Type 8) is the most appropriate first step for identifying live hosts on a network because it is a standard, low-disruption method that quickly determines host availability. ICMP echo requests are typically allowed by default on many networks and do not initiate full protocol handshakes or service interactions, minimizing the risk of triggering alarms or causing instability. This aligns with the penetration testing methodology of starting with passive or low-impact reconnaissance before escalating to more intrusive techniques.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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