CEH Footprinting, Reconnaissance and Scanning Practice Question
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 TWO of the following Nmap flags can be used to bypass firewall restrictions? (Select 2)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
-f (fragment packets)
Option B is correct because the -f flag fragments packets into smaller 8-byte chunks, which can evade simple firewall rules that inspect packet headers for known signatures or block oversized packets. Option E is correct because the -D flag performs a decoy scan by spoofing multiple source IP addresses, making it difficult for a firewall to identify the true scanning host and block it.
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.
✗
-P0 (disable ping)
Why it's wrong here
-P0 (now -Pn) skips host discovery but doesn't bypass firewalls; it assumes hosts are up.
✓
-f (fragment packets)
Why this is correct
Fragmentation can bypass simple firewalls that don't reassemble packets.
Related concept
Read the scenario before looking for a memorised answer.
✗
-T4 (aggressive timing)
Why it's wrong here
Timing templates affect speed, not firewall evasion.
✗
-sS (SYN scan)
Why it's wrong here
SYN scan is stealthy but not a specific firewall bypass technique.
✓
-D (decoy scan)
Why this is correct
Decoy scan makes it harder for firewalls to identify the true source.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse stealth scanning (-sS) with firewall evasion, not realizing that SYN scans are still detectable by modern firewalls that track connection states, while fragmentation and decoys directly manipulate packet structure or source identity to bypass filters.
Detailed technical explanation
How to think about this question
Packet fragmentation (-f) works by splitting the TCP header across multiple IP fragments, causing some firewalls to reassemble incorrectly or pass fragments without inspection, as per RFC 791. Decoy scanning (-D) leverages IP spoofing to generate noise from multiple source addresses, forcing the firewall to process many seemingly legitimate scans and potentially failing to block the true source. In real-world penetration tests, combining -f with -D can bypass stateful inspection firewalls that lack deep packet inspection or fragment reassembly capabilities.
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 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: -f (fragment packets) — Option B is correct because the -f flag fragments packets into smaller 8-byte chunks, which can evade simple firewall rules that inspect packet headers for known signatures or block oversized packets. Option E is correct because the -D flag performs a decoy scan by spoofing multiple source IP addresses, making it difficult for a firewall to identify the true scanning host and block it.
What should I do if I get this CEH question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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