SY0-701 Threats, Vulnerabilities, and Mitigations Practice Question
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?
⚠ Common exam trap
Watch out — candidates often confuse 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.
Answer choices
Why each option matters
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.
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 exhausts a target's TCP connection table with half-open handshakes; it involves no DNS resolvers and no forged queries to third parties. It tempts as a volumetric denial-of-service, but the reflected DNS responses from open resolvers identify DNS amplification instead.
- ✓
DNS amplification DDoS
Why this is correct
The attacker sends small forged queries to many open resolvers, which return much larger responses to the spoofed victim address. This reflection and amplification saturates the target's bandwidth, matching the widely varying source IPs and DNS response flood.
- ✗
Replay attack
Why it's wrong here
A replay attack retransmits previously captured valid authentication or session data to impersonate a legitimate party; it generates no flood of DNS responses. It tempts because captured traffic is reused, but the described amplification via open resolvers with spoofed queries is a DNS amplification attack.
- ✗
Man-in-the-middle attack
Why it's wrong here
A man-in-the-middle attack intercepts or alters traffic between two communicating parties, typically via ARP spoofing or rogue proxies. Here the victim receives unsolicited DNS responses from many third-party resolvers, which is DNS amplification/reflection, not interception. MitM would be the answer where an attacker secretly relays and possibly modifies traffic between two endpoints.
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Related to this question
Learn chapter
DoS and DDoS Attacks
Key term
DNS
DNS is the system that translates human-friendly domain names like example.com into machine-readable IP addresses so computers can find each other on a network.
Key term
Denial-of-service
A Denial-of-service (DoS) attack is an attempt to make a computer, network, or online service unavailable to its intended users by overwhelming it with fake traffic or requests.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SY0-701 practice question is part of Courseiva's free CompTIA 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 SY0-701 exam.