N10-009 Network Security Practice Question
A security analyst observes that a workstation on the network is sending unsolicited ARP replies stating that the workstation's MAC address corresponds to the default gateway IP for all subnets. This behavior is causing other devices to send traffic destined for external networks to the workstation instead of the legitimate gateway. Which type of attack is being performed?
⚠ Common exam trap
Watch out — candidates often confuse ARP spoofing with MAC flooding, because both involve MAC addresses and network interception, but MAC flooding targets the switch's CAM table to capture traffic, while ARP spoofing targets host ARP caches to redirect traffic to a specific MAC address.
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
✓
A: ARP spoofing
The workstation is sending unsolicited ARP replies that map the default gateway IP to its own MAC address. This poisons the ARP caches of other devices on the network, causing them to forward traffic destined for external networks to the attacker's workstation instead of the legitimate gateway. This is the classic behavior of an ARP spoofing (or ARP poisoning) attack, which exploits the lack of authentication in the ARP protocol (RFC 826).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
A: ARP spoofing
Why this is correct
ARP spoofing is a Layer 2 attack where an attacker sends forged Address Resolution Protocol (ARP) messages over a local area network. The goal is to associate the attacker's MAC address with the IP address of another host, most commonly the default gateway. By doing this, the attacker intercepts traffic intended for the gateway, effectively positioning themselves as a "man-in-the-middle" between the victim and the actual gateway, allowing for eavesdropping or manipulation of data.
- ✗
B: DHCP starvation
Why it's wrong here
DHCP starvation is a denial-of-service attack where an attacker floods a DHCP server with numerous bogus DHCP requests, often using spoofed MAC addresses. The objective is to exhaust the server's available IP address pool, preventing legitimate clients from obtaining network configurations and accessing the network. While it disrupts network services, this attack focuses on IP address allocation and does not involve a workstation claiming the gateway's IP via ARP replies.
When this WOULD be correct
A DHCP starvation attack would be correct if the question described an attacker sending numerous DHCPDISCOVER messages to exhaust the DHCP server's address pool, preventing legitimate clients from obtaining IP addresses.
- ✗
C: DNS poisoning
Why it's wrong here
DNS poisoning, also known as DNS cache poisoning, is an attack where corrupted Domain Name System (DNS) data is introduced into a DNS resolver's cache. This causes the resolver to return an incorrect IP address for a legitimate domain name, redirecting users to malicious websites. This attack operates at the application layer (Layer 7) and does not involve a workstation directly claiming the gateway's IP address using Layer 2 protocols like ARP.
When this WOULD be correct
A question where users report being redirected to a phishing site when typing a legitimate domain name, and the attack is traced to a compromised DNS server or cache poisoning.
- ✗
D: MAC flooding
Why it's wrong here
MAC flooding is an attack targeting network switches, where an attacker sends a large number of Ethernet frames with unique, spoofed source MAC addresses. This action overwhelms the switch's Content Addressable Memory (CAM) table, forcing it to enter a "fail-open" mode where it behaves like a hub, broadcasting all traffic to all ports. While it can facilitate eavesdropping, it does not involve a workstation sending ARP replies to claim the gateway's IP address.
When this WOULD be correct
A security analyst notices that the switch's MAC address table is full and the switch begins flooding unicast traffic to all ports. Which attack is being performed?
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓A: ARP spoofingCorrect answer▾
Why this is correct
ARP spoofing is a Layer 2 attack where an attacker sends forged Address Resolution Protocol (ARP) messages over a local area network. The goal is to associate the attacker's MAC address with the IP address of another host, most commonly the default gateway. By doing this, the attacker intercepts traffic intended for the gateway, effectively positioning themselves as a "man-in-the-middle" between the victim and the actual gateway, allowing for eavesdropping or manipulation of data.
✗B: DHCP starvationWrong answer — click to see why▾
Why this is wrong here
DHCP starvation floods a DHCP server with requests to exhaust its IP address pool, causing denial of service. The question describes unsolicited ARP replies mapping the attacker's MAC to the gateway IP, which is ARP spoofing, not DHCP-related.
★ When this WOULD be the correct answer
A DHCP starvation attack would be correct if the question described an attacker sending numerous DHCPDISCOVER messages to exhaust the DHCP server's address pool, preventing legitimate clients from obtaining IP addresses.
Why candidates choose this
Candidates may confuse DHCP starvation with ARP spoofing because both involve network-layer manipulation and can disrupt traffic flow, but they target different protocols (DHCP vs. ARP).
✗C: DNS poisoningWrong answer — click to see why▾
Why this is wrong here
DNS poisoning involves corrupting DNS resolver caches to redirect domain names to malicious IPs, not manipulating ARP tables with unsolicited replies for the default gateway IP.
★ When this WOULD be the correct answer
A question where users report being redirected to a phishing site when typing a legitimate domain name, and the attack is traced to a compromised DNS server or cache poisoning.
Why candidates choose this
Candidates may confuse 'poisoning' attacks (ARP vs. DNS) and think any redirection of traffic involves DNS, overlooking the Layer 2 ARP mechanism described.
✗D: MAC floodingWrong answer — click to see why▾
Why this is wrong here
MAC flooding involves sending many frames with different source MAC addresses to overflow the switch's MAC address table, causing it to fail open and broadcast traffic. The question describes unsolicited ARP replies, not MAC table overflow.
★ When this WOULD be the correct answer
A security analyst notices that the switch's MAC address table is full and the switch begins flooding unicast traffic to all ports. Which attack is being performed?
Why candidates choose this
Candidates may confuse MAC flooding with ARP spoofing because both involve manipulating network traffic, but MAC flooding targets the switch's forwarding table rather than ARP caches.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Quick reference
IPv4 Address Class Summary
| Class | First Octet Range | Default Mask | Networks | Hosts per Network |
|---|---|---|---|---|
| A | 1–126 | /8 (255.0.0.0) | 126 | 16,777,214 |
| B | 128–191 | /16 (255.255.0.0) | 16,384 | 65,534 |
| C | 192–223 | /24 (255.255.255.0) | 2,097,152 | 254 |
| D | 224–239 | N/A | Multicast groups | — |
| E | 240–255 | N/A | Reserved / experimental | — |
127.x.x.x is reserved for loopback. Modern networks use CIDR (classless) rather than classful addressing.
Go deeper
Related to this question
Learn chapter
Network Device Hardening
Key term
MAC address
A MAC address is a unique hardware identifier assigned to a network interface card that allows devices to communicate on a local network.
Key term
Address Resolution Protocol
Address Resolution Protocol (ARP) is a network protocol that maps a device's IP address to its physical MAC address so data can travel across a local network.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This N10-009 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 N10-009 exam.