DNS Poisoning vs ARP Spoofing: How to Tell Them Apart
Users on the internal Wi-Fi report that the finance portal suddenly resolves to a different IP address, and the browser shows a fake login page that closely matches the real site. The DNS resolver cache on the network also contains unexpected entries for that host name. What attack is most likely?
Quick Answer
The answer is DNS poisoning, because the attacker has corrupted the name resolution process to redirect users to a malicious IP address. This attack works by injecting forged DNS records into a resolver’s cache, so when users type the finance portal’s hostname, the DNS server returns the attacker’s fake IP instead of the legitimate one. The telltale sign here is the unexpected entries in the DNS resolver cache—ARP spoofing would instead corrupt the MAC-to-IP mapping at Layer 2, not the DNS cache. On the Security+ SY0-701 exam, this scenario tests your ability to distinguish between attacks on name resolution (DNS poisoning) versus attacks on local network addressing (ARP spoofing). A common trap is confusing the two because both can redirect traffic, but DNS poisoning affects all users system-wide, while ARP spoofing is limited to a single subnet. Memory tip: “DNS corrupts the directory, ARP corrupts the address.”
⚠ Common exam trap
It's easy for candidates to confuse ARP spoofing with DNS poisoning because both can redirect traffic, but ARP spoofing operates at Layer 2 and does not affect DNS resolver cache entries, whereas DNS poisoning directly corrupts the name resolution database.
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 poisoning, because the attacker has corrupted name resolution so users are sent to a malicious destination.
B is correct because DNS poisoning (also known as DNS cache poisoning) directly corrupts the name resolution process, causing the finance portal's hostname to resolve to a malicious IP address. The presence of unexpected DNS resolver cache entries for that hostname confirms that the attack targeted the DNS infrastructure, not the ARP table or network availability.
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 spoofing, because the attacker is changing the MAC address used on the local network.
Why it's wrong here
ARP spoofing targets Layer 2 address resolution, usually affecting traffic within the same local segment. The key symptom here is a changed name resolution result in DNS.
- ✓
DNS poisoning, because the attacker has corrupted name resolution so users are sent to a malicious destination.
Why this is correct
DNS poisoning fits the evidence because the resolver cache contains bad entries and users are being directed to a fake site through altered name resolution. That lets the attacker redirect traffic without changing the user’s bookmarks or typing habits.
- ✗
Port scanning, because the attacker is probing internal services for open ports.
Why it's wrong here
Port scanning is reconnaissance against services, not a method for redirecting a domain name to a counterfeit web page.
- ✗
Denial-of-service, because the attacker is overwhelming the portal with traffic.
Why it's wrong here
A denial-of-service attack aims to exhaust availability, usually by flooding a target. Here, the attacker is serving a fake destination rather than making the real site unavailable.
Visual reference
Go deeper
Related to this question
Learn chapter
Network-Based Attacks
Key term
ARP table
An ARP table is a data structure stored on a network device that maps IP addresses to their corresponding MAC addresses, enabling communication within a local network.
Key term
Availability
Availability is the measure of how often a system or service is operational and accessible when needed, typically expressed as a percentage of uptime.
About these practice questions
Courseiva writes every SY0-701 question from scratch — 1,013 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
Same concept, more angles
2 more ways this is tested on SY0-701
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Users on a wired subnet report intermittent outages when reaching an internal application. A packet capture shows the default gateway IP address repeatedly mapped to a different workstation MAC address, and traffic is being forwarded through that workstation. What attack is most likely occurring?
medium- A.DNS poisoning, because the hostname is resolving to the wrong server.
- ✓ B.ARP spoofing, because false Layer 2 address mappings are redirecting traffic.
- C.Replay attack, because packets are being resent to the gateway.
- D.Rogue DHCP service, because clients are losing access to the default gateway.
Why B: B is correct because ARP spoofing (also known as ARP poisoning) involves an attacker sending forged ARP messages over a local area network. This results in the attacker's MAC address being associated with the IP address of the default gateway, causing traffic destined for the gateway to be forwarded to the attacker's workstation instead. The packet capture evidence of the default gateway IP repeatedly mapped to a different workstation MAC address is the classic signature of this attack.
Variation 2. Several users on the same subnet report that their traffic to the default gateway is intermittently slow and sometimes reaches the wrong device. A packet capture shows ARP replies that map the gateway IP to a different MAC address. What attack is most likely occurring?
easy- ✓ A.ARP spoofing, which poisons address resolution on the local network
- B.DNS amplification, which overwhelms the target with reflected DNS traffic
- C.Replay attack, which resends captured authentication data
- D.Port scanning, which probes hosts for open services and ports
Why A: ARP spoofing (also known as ARP poisoning) is the correct answer because the attacker sends forged ARP replies that associate the default gateway's IP address with the attacker's MAC address. This causes the victims' ARP caches to update with the false mapping, so traffic destined for the gateway is instead sent to the attacker, leading to intermittent connectivity and misrouted packets. The symptoms—slow traffic and reaching the wrong device—are classic indicators of a man-in-the-middle (MITM) attack via ARP cache poisoning. (Switches maintain MAC address tables, not ARP caches.)
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.