The answer is ARP spoofing, also known as ARP poisoning. This attack is the most likely cause because the packet capture shows forged ARP replies that map the gateway IP to a different MAC address, and the same host sends these unsolicited replies repeatedly, which is a classic sign of an attacker trying to redirect traffic through their machine. On the Security+ SY0-701 exam, this scenario tests your ability to recognize network-based man-in-the-middle attacks, where the attacker intercepts traffic by corrupting the ARP cache of hosts on the local subnet. A common trap is confusing this with a MAC flooding attack, but remember that MAC flooding overwhelms a switch’s CAM table, while ARP spoofing specifically targets the IP-to-MAC mapping in a host’s ARP table. Memory tip: think “ARP = Address Resolution Poisoning” to link the forged replies with the poisoning of the cache.
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.
Several users on the same subnet report intermittent inability to reach the default gateway. A packet capture shows ARP replies mapping the gateway IP to a different MAC address, and the same host keeps sending those replies every few seconds. 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ARP spoofing
The correct answer is B, ARP spoofing. The symptoms—intermittent gateway unreachability, ARP replies mapping the gateway IP to a different MAC address, and repeated unsolicited ARP replies—are classic indicators of an ARP spoofing (also called ARP poisoning) attack. The attacker sends forged ARP replies to associate their own MAC address with the gateway IP, causing traffic destined for the gateway to be sent to the attacker instead, disrupting connectivity.
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.
✗
Replay attack
Why it's wrong here
A replay attack reuses captured valid traffic later, but the key clue here is false ARP information on the local network.
✓
ARP spoofing
Why this is correct
ARP spoofing, also called ARP poisoning, forges ARP replies so hosts associate the gateway IP with the attacker MAC address.
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.
✗
DNS amplification
Why it's wrong here
DNS amplification relies on reflected DNS traffic and large response volumes, not altered ARP mappings on a local subnet.
✗
Man-in-the-middle via TLS downgrade
Why it's wrong here
A man-in-the-middle can happen in many ways, but the capture specifically shows forged ARP replies rather than a TLS issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse ARP spoofing with a man-in-the-middle attack in general, but the question specifically describes ARP-level manipulation (forged ARP replies mapping the gateway IP to a different MAC), which is the defining characteristic of ARP spoofing, not a TLS downgrade or replay attack.
Trap categories for this question
Command / output trap
A man-in-the-middle can happen in many ways, but the capture specifically shows forged ARP replies rather than a TLS issue.
Detailed technical explanation
How to think about this question
ARP spoofing exploits the lack of authentication in the Address Resolution Protocol (RFC 826). The attacker sends gratuitous ARP replies (often with a target IP of the gateway and a target MAC of the attacker's NIC) to poison the ARP cache of hosts on the subnet. This can be used to intercept traffic (man-in-the-middle) or cause a denial of service by dropping packets; tools like Ettercap or arpspoof automate this. In real-world scenarios, ARP spoofing is often a precursor to session hijacking or credential theft on local networks.
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 developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
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: ARP spoofing — The correct answer is B, ARP spoofing. The symptoms—intermittent gateway unreachability, ARP replies mapping the gateway IP to a different MAC address, and repeated unsolicited ARP replies—are classic indicators of an ARP spoofing (also called ARP poisoning) attack. The attacker sends forged ARP replies to associate their own MAC address with the gateway IP, causing traffic destined for the gateway to be sent to the attacker instead, disrupting connectivity.
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.
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