This N10-009 practice question tests your understanding of network security. 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 security analyst detects that an attacker is sending forged ARP replies to associate the attacker's MAC address with the IP address of the default gateway. What is this attack called?
ARP poisoning directly exploits the ARP protocol by injecting false entries into a target's ARP cache, redirecting traffic destined for the gateway to the attacker.
B
MAC flooding
Why wrong: MAC flooding sends many frames with different source MAC addresses to overflow the switch's MAC table, causing the switch to fail open into a hub-like state. It does not specifically target the gateway's IP.
C
DHCP snooping
Why wrong: DHCP snooping is a security feature on switches to prevent rogue DHCP servers. It is not an attack; it is a mitigation technique.
D
DNS spoofing
Why wrong: DNS spoofing corrupts DNS resolution to redirect traffic to malicious sites, but it operates at the application layer and does not involve ARP.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ARP poisoning
ARP poisoning (also known as ARP spoofing) is the correct answer because the attacker sends forged ARP replies to associate their MAC address with the IP address of the default gateway. This causes the victim's switch to update its ARP cache with the attacker's MAC for the gateway's IP, enabling man-in-the-middle attacks where the attacker intercepts traffic destined for the gateway.
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.
✓
ARP poisoning
Why this is correct
ARP poisoning directly exploits the ARP protocol by injecting false entries into a target's ARP cache, redirecting traffic destined for the gateway to the attacker.
Related concept
Read the scenario before looking for a memorised answer.
✗
MAC flooding
Why it's wrong here
MAC flooding sends many frames with different source MAC addresses to overflow the switch's MAC table, causing the switch to fail open into a hub-like state. It does not specifically target the gateway's IP.
✗
DHCP snooping
Why it's wrong here
DHCP snooping is a security feature on switches to prevent rogue DHCP servers. It is not an attack; it is a mitigation technique.
✗
DNS spoofing
Why it's wrong here
DNS spoofing corrupts DNS resolution to redirect traffic to malicious sites, but it operates at the application layer and does not involve ARP.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between ARP poisoning (which targets the ARP cache) and MAC flooding (which targets the switch's CAM table), leading candidates to confuse the two because both involve MAC addresses and network attacks.
Detailed technical explanation
How to think about this question
Under the hood, ARP poisoning exploits the stateless nature of ARP; hosts accept unsolicited ARP replies (gratuitous ARPs) without verification. In a real-world scenario, an attacker could combine ARP poisoning with DNS spoofing to redirect traffic to a malicious site, bypassing network security controls. Tools like Ettercap or arpspoof automate this by sending crafted ARP packets at intervals to maintain the poisoned cache.
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 practitioner preparing for the N10-009 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ARP poisoning — ARP poisoning (also known as ARP spoofing) is the correct answer because the attacker sends forged ARP replies to associate their MAC address with the IP address of the default gateway. This causes the victim's switch to update its ARP cache with the attacker's MAC for the gateway's IP, enabling man-in-the-middle attacks where the attacker intercepts traffic destined for the gateway.
What should I do if I get this N10-009 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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