- A
DNS
Why wrong: The user is connecting by IP address, not hostname, so DNS is not used.
- B
DHCP
Why wrong: DHCP assigns IP addresses, but the computer already has an IP and can access the internet, so DHCP is working.
- C
ARP
ARP resolves the printer's IP to its MAC address. If ARP fails, the computer cannot send frames to the printer, causing ping failure.
- D
NAT
Why wrong: NAT is used for traffic between different networks; the printer is on the same subnet, so NAT is not involved.
Question 429 of 1,020
ARP Failure: Why Pinging a Device on the Same Subnet Fails
This 220-1201 practice question tests your understanding of network services. 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.
A technician is troubleshooting an issue where a user's computer can access the internet but cannot connect to a network printer by its IP address. The printer is on the same subnet and is powered on. Pinging the printer's IP from the computer fails. Which network service is most likely causing the problem?
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.
Quick Answer
The answer is ARP, or Address Resolution Protocol, because when pinging a device on the same subnet, the computer must resolve the target IP address to its corresponding MAC address before any data can be sent. Since the printer is on the same subnet, no router or default gateway is involved, so the failure lies in the ARP process—if the computer cannot obtain the printer’s MAC address, the ping will simply time out. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of when ARP is used versus DNS or DHCP; a common trap is assuming DNS is the issue when connecting by IP, but DNS only resolves names, not IP-to-MAC mappings. Remember that ARP operates at Layer 2 of the OSI model and is essential for same-subnet communication. A helpful memory tip: “Same subnet, same switch—ARP is the missing piece.”
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
Since the computer can access the internet but cannot ping the printer on the same subnet, the issue is at Layer 2 (Data Link) rather than Layer 3 (Network). ARP (Address Resolution Protocol) is responsible for resolving a known IP address to a MAC address on the local subnet. If the ARP cache is corrupted, missing, or the printer fails to respond to ARP requests, the computer cannot build the correct Ethernet frame to reach the printer, causing the ping to fail even though the printer is powered on and on the same subnet.
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
Why it's wrong here
The user is connecting by IP address, not hostname, so DNS is not used.
- ✗
DHCP
Why it's wrong here
DHCP assigns IP addresses, but the computer already has an IP and can access the internet, so DHCP is working.
- ✓
ARP
Why this is correct
ARP resolves the printer's IP to its MAC address. If ARP fails, the computer cannot send frames to the printer, causing ping failure.
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.
- ✗
NAT
Why it's wrong here
NAT is used for traffic between different networks; the printer is on the same subnet, so NAT is not involved.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA A+ often tests the misconception that a failed ping to a local IP must be a Layer 3 routing or DNS issue, when in fact the problem is often a missing or incorrect ARP entry at Layer 2.
Detailed technical explanation
How to think about this question
When a host pings another host on the same subnet, it first checks its ARP cache for the target IP's MAC address. If no entry exists, it broadcasts an ARP request (destination MAC FF:FF:FF:FF:FF:FF) asking 'Who has this IP?'. If the printer does not respond (e.g., due to a firewall blocking ARP, a misconfigured static ARP entry, or a switch port issue), the ping fails with 'Destination Host Unreachable'. The `arp -a` command on Windows or `ip neigh` on Linux can be used to inspect the ARP table and verify if the printer's MAC is present.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this 220-1201 question test?
Network Services — This question tests Network Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ARP — Since the computer can access the internet but cannot ping the printer on the same subnet, the issue is at Layer 2 (Data Link) rather than Layer 3 (Network). ARP (Address Resolution Protocol) is responsible for resolving a known IP address to a MAC address on the local subnet. If the ARP cache is corrupted, missing, or the printer fails to respond to ARP requests, the computer cannot build the correct Ethernet frame to reach the printer, causing the ping to fail even though the printer is powered on and on the same subnet.
What should I do if I get this 220-1201 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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Last reviewed: Jul 4, 2026
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