This 200-201 practice question tests your understanding of security monitoring. 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.
During a security incident, a network engineer captures traffic with tcpdump and saves it to a pcap file. The analyst needs to extract all HTTP POST requests containing a specific string in the URI. Which command should be used?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
tcpdump -r traffic.pcap 'tcp port 80' -A | grep 'POST' | grep 'string'
Option B is correct because it uses tcpdump with the `-r` flag to read the pcap file, filters for TCP port 80 (HTTP), uses `-A` to print packet payloads in ASCII, and then pipes the output through two grep commands: first to isolate lines containing 'POST' (indicating HTTP POST requests) and second to filter for the specific string in the URI. This combination efficiently extracts only the relevant HTTP POST requests with the target string from the captured traffic.
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.
✗
tcpdump -r traffic.pcap -X | grep 'string'
Why it's wrong here
-X prints hex and ASCII; not focused on POST URI.
✓
tcpdump -r traffic.pcap 'tcp port 80' -A | grep 'POST' | grep 'string'
Why this is correct
Reads pcap, filters HTTP, prints ASCII, then greps for POST and string.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
ngrep -q -W byline 'POST.*string' port 80
Why it's wrong here
ngrep is not tcpdump, and -W byline might not extract full request.
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between reading a pcap file with `-r` versus capturing live traffic, and the trap here is that candidates may forget to include the `-A` flag for ASCII output or the `tcp port 80` filter, leading to incomplete or irrelevant results.
Detailed technical explanation
How to think about this question
HTTP POST requests are sent over TCP port 80 (or 443 for HTTPS), and the request line begins with 'POST' followed by the URI. The `-A` flag in tcpdump prints the packet payload in ASCII, which is essential for reading HTTP headers and URIs. In a real-world incident, an analyst might need to extract POST requests containing a malicious payload string like '/login?user=admin' to identify a brute-force attack, and piping through multiple grep commands allows precise filtering without needing a full packet analysis tool like Wireshark.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Monitoring — This question tests Security Monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: tcpdump -r traffic.pcap 'tcp port 80' -A | grep 'POST' | grep 'string' — Option B is correct because it uses tcpdump with the `-r` flag to read the pcap file, filters for TCP port 80 (HTTP), uses `-A` to print packet payloads in ASCII, and then pipes the output through two grep commands: first to isolate lines containing 'POST' (indicating HTTP POST requests) and second to filter for the specific string in the URI. This combination efficiently extracts only the relevant HTTP POST requests with the target string from the captured traffic.
What should I do if I get this 200-201 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: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
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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