- A
DNS poisoning, because the workstation name may be resolving to the wrong IP address.
Why wrong: DNS poisoning affects name resolution records, but the symptom here is an ARP cache mapping the gateway IP to the wrong MAC address on the local network.
- B
ARP poisoning, because false ARP replies are redirecting gateway traffic to another host.
ARP poisoning fits exactly when a host sends falsified ARP information so victims associate the gateway IP with the attacker’s MAC address. That can enable interception, disruption, or man-in-the-middle behavior on the local subnet.
- C
Replay attack, because the attacker is reusing old network frames to confuse the hosts.
Why wrong: Replay attacks involve captured traffic being resent later. The clue here is a poisoned ARP table, not the reuse of valid packets or timestamps.
- D
Denial of service, because traffic eventually times out and connectivity is lost.
Why wrong: DoS can cause outages, but the explicit evidence of wrong ARP mappings identifies the mechanism. The timeout is a result of the poisoning, not the root cause itself.
Quick Answer
The answer is ARP poisoning, because false ARP replies are redirecting gateway traffic to another host. This attack exploits the lack of authentication in the Address Resolution Protocol, allowing an attacker to send forged ARP replies that map the gateway’s IP address to the attacker’s MAC address. As a result, hosts in VLAN 20 update their ARP caches with this false mapping, sending traffic meant for the default gateway directly to the attacker’s workstation, where it is briefly forwarded or dropped, causing the random timeouts described. On the Security+ SY0-701 exam, this scenario tests your ability to recognize a man-in-the-middle attack via ARP cache corruption, often disguised as a simple connectivity issue. A common trap is confusing this with a DHCP starvation attack, but remember: ARP poisoning corrupts the IP-to-MAC mapping, not the IP lease itself. Memory tip: “Poison the cache, reroute the traffic.”
SY0-701 Threats, Vulnerabilities, and Mitigations Practice Question
This SY0-701 practice question tests your understanding of threats, vulnerabilities, and mitigations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 troubleshooting, several hosts in VLAN 20 lose access to the default gateway at random. Their ARP caches now map the gateway IP to a workstation MAC address, and traffic briefly flows through that workstation before timing out. What attack is most likely?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
ARP poisoning, because false ARP replies are redirecting gateway traffic to another host.
Option B is correct because the scenario describes classic ARP poisoning (also known as ARP spoofing). The attacker sends forged ARP replies to the hosts in VLAN 20, associating the gateway's IP address with the attacker's MAC address. This causes the hosts to forward traffic destined for the gateway to the attacker's workstation, where it is briefly forwarded (or dropped) before timing out, matching the symptoms of a man-in-the-middle attack via ARP cache corruption.
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.
- ✗
DNS poisoning, because the workstation name may be resolving to the wrong IP address.
Why it's wrong here
DNS poisoning affects name resolution records, but the symptom here is an ARP cache mapping the gateway IP to the wrong MAC address on the local network.
- ✓
ARP poisoning, because false ARP replies are redirecting gateway traffic to another host.
Why this is correct
ARP poisoning fits exactly when a host sends falsified ARP information so victims associate the gateway IP with the attacker’s MAC address. That can enable interception, disruption, or man-in-the-middle behavior on the local subnet.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Replay attack, because the attacker is reusing old network frames to confuse the hosts.
Why it's wrong here
Replay attacks involve captured traffic being resent later. The clue here is a poisoned ARP table, not the reuse of valid packets or timestamps.
- ✗
Denial of service, because traffic eventually times out and connectivity is lost.
Why it's wrong here
DoS can cause outages, but the explicit evidence of wrong ARP mappings identifies the mechanism. The timeout is a result of the poisoning, not the root cause itself.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests ARP poisoning by describing symptoms of gateway loss and ARP cache corruption, and the trap here is that candidates may confuse it with DNS poisoning because both involve redirection, but ARP poisoning operates at Layer 2 (MAC address) while DNS poisoning operates at Layer 7 (name resolution).
Detailed technical explanation
How to think about this question
ARP poisoning exploits the stateless nature of ARP (RFC 826); hosts accept unsolicited ARP replies without authentication. Tools like Ettercap or arpspoof send gratuitous ARP packets to poison the target's cache. In a switched VLAN, the attack can still succeed because ARP broadcasts are confined to the VLAN, but the attacker must be on the same broadcast domain or use VLAN hopping techniques. The brief flow of traffic through the workstation occurs because the attacker may enable IP forwarding (e.g., via sysctl net.ipv4.ip_forward=1 on Linux) to act as a man-in-the-middle, but if forwarding is disabled, traffic is dropped, causing timeouts.
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 security analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this SY0-701 question test?
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: ARP poisoning, because false ARP replies are redirecting gateway traffic to another host. — Option B is correct because the scenario describes classic ARP poisoning (also known as ARP spoofing). The attacker sends forged ARP replies to the hosts in VLAN 20, associating the gateway's IP address with the attacker's MAC address. This causes the hosts to forward traffic destined for the gateway to the attacker's workstation, where it is briefly forwarded (or dropped) before timing out, matching the symptoms of a man-in-the-middle attack via ARP cache corruption.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 30, 2026
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.
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