This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. 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.
Which of the following techniques is considered PASSIVE reconnaissance?
Ping sweeping a subnet
Why wrong: Ping sweep sends ICMP packets to hosts, which is active.
Banner grabbing with Telnet
Why wrong: Banner grabbing connects to a service on the target, making it active.
Running a SYN scan with Nmap
Why wrong: SYN scan sends packets to the target, making it active.
Performing a WHOIS lookup
WHOIS queries public databases and does not interact with the target's systems.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Performing a WHOIS lookup
WHOIS queries retrieve domain registration records from public databases like whois.iana.org or RDAP servers. Since the target server is never contacted directly — only public registries are queried — no packets are sent to the target's infrastructure, making it a purely passive reconnaissance technique.
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 sweeping a subnet
Why it's wrong here
Ping sweep sends ICMP packets to hosts, which is active.
Banner grabbing with Telnet
Why it's wrong here
Banner grabbing connects to a service on the target, making it active.
Running a SYN scan with Nmap
Why it's wrong here
SYN scan sends packets to the target, making it active.
Performing a WHOIS lookup
Why this is correct
WHOIS queries public databases and does not interact with the target's systems.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
EC-Council often tests the distinction between passive and active reconnaissance by making candidates think that any network-based query (like WHOIS) is active, when in fact WHOIS queries public third-party databases, not the target's own systems.
Detailed technical explanation
Passive reconnaissance relies on publicly available information without direct interaction with the target. WHOIS uses TCP port 43 (or HTTP/HTTPS for RDAP) to query registrar databases, not the target's own servers. A subtle behavior: WHOIS responses can reveal registrar, name servers, and creation/expiration dates, which help an attacker map the target's infrastructure without generating any logs on the target's systems.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
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FAQ
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
The correct answer is: Performing a WHOIS lookup — WHOIS queries retrieve domain registration records from public databases like whois.iana.org or RDAP servers. Since the target server is never contacted directly — only public registries are queried — no packets are sent to the target's infrastructure, making it a purely passive reconnaissance technique.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This CEH practice question is part of Courseiva's free EC-Council 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 CEH exam.
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