The correct answer is a DNS amplification DDoS attack. This is because the attacker exploits open DNS resolvers by sending small, forged queries with the victim’s spoofed IP address, causing those resolvers to flood the victim with much larger DNS responses—a classic reflection and amplification technique that saturates the target’s bandwidth. On the Security+ SY0-701 exam, this scenario tests your understanding of DDoS attack vectors, specifically how attackers leverage UDP-based services to multiply traffic while hiding behind a wide range of legitimate source IPs, making mitigation via simple IP blocking ineffective. A common trap is confusing this with a simple DNS cache poisoning or a SYN flood; remember that amplification attacks rely on a massive size disparity between the request and the response. Memory tip: think “small query, big reply” to recall the amplification factor.
SY0-701 Threats, Vulnerabilities, and Mitigations Practice Question
This SY0-701 practice question tests your understanding of threats, vulnerabilities, and mitigations. 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 public website is overwhelmed by a flood of DNS responses arriving from many open resolvers after the attacker sends small forged queries to those resolvers. The target bandwidth is saturated and the source IPs vary widely. What kind of attack is being used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DNS amplification DDoS
B is correct because this scenario describes a DNS amplification DDoS attack. The attacker sends small forged DNS queries with a spoofed source IP (the victim's IP) to open resolvers, which respond with much larger DNS replies. The flood of amplified responses saturates the victim's bandwidth, and the varying source IPs make mitigation difficult. This matches the description of a reflection/amplification attack using DNS.
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.
✗
SYN flood
Why it's wrong here
A SYN flood targets TCP handshake state, but this scenario is centered on DNS responses from third-party resolvers.
✓
DNS amplification DDoS
Why this is correct
DNS amplification uses small spoofed requests to trigger much larger replies from reflectors, multiplying traffic toward the victim.
Related concept
Read the scenario before looking for a memorised answer.
✗
Replay attack
Why it's wrong here
Replay attacks resend captured legitimate messages, but they do not create a large reflected response stream from resolvers.
✗
Man-in-the-middle attack
Why it's wrong here
A man-in-the-middle intercepts or alters traffic between parties, but the described symptom is bandwidth exhaustion from reflected traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing a DNS amplification attack with a SYN flood because both involve flooding, but the key differentiator is the use of DNS responses from open resolvers versus incomplete TCP handshakes.
Trap categories for this question
Scenario analysis trap
A SYN flood targets TCP handshake state, but this scenario is centered on DNS responses from third-party resolvers.
Detailed technical explanation
How to think about this question
DNS amplification exploits the fact that a small query (e.g., 60 bytes for an ANY record) can generate a response up to 4000 bytes, giving an amplification factor of ~70x. Attackers use open resolvers that respond to recursive queries from any source, and they spoof the victim's IP in the source field of the query. This attack is mitigated by disabling open recursion, implementing Response Rate Limiting (RRL), and using BCP38 ingress filtering to prevent IP spoofing.
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 SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this SY0-701 question in full detail.
Threats, Vulnerabilities, and Mitigations — This question tests Threats, Vulnerabilities, and Mitigations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: DNS amplification DDoS — B is correct because this scenario describes a DNS amplification DDoS attack. The attacker sends small forged DNS queries with a spoofed source IP (the victim's IP) to open resolvers, which respond with much larger DNS replies. The flood of amplified responses saturates the victim's bandwidth, and the varying source IPs make mitigation difficult. This matches the description of a reflection/amplification attack using DNS.
What should I do if I get this SY0-701 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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