- A
The switch is blocking the traffic due to MAC address filtering.
Why wrong: MAC filtering would block specific devices, but it would not explain why two devices on different subnets cannot communicate.
- B
The computers are on different subnets and need a router to communicate.
Computers on different subnets cannot communicate directly; they require a router to forward packets between the subnets.
- C
The subnet mask on Computer B is incorrect.
Why wrong: The subnet mask is correct for its own subnet (255.255.255.0), but the problem is that they are on different subnets.
- D
The default gateway on both computers is not set.
Why wrong: A default gateway is needed to reach other subnets, but even if set, it would not enable direct communication without a router.
Quick Answer
The answer is that the computers cannot communicate because they are on different subnets and require a router to forward traffic between them. Even though both devices are connected to the same physical switch, their IP addresses—192.168.1.10 and 192.168.2.20—belong to separate logical subnets (192.168.1.0/24 and 192.168.2.0/24). A switch operates at Layer 2 and only forwards frames within the same broadcast domain; it cannot route packets between different subnets. On the CompTIA A+ Core 1 220-1201 exam, this scenario tests your understanding of the difference between switching and routing, and it often appears as a trick question where students assume a physical connection guarantees communication. The common trap is forgetting that subnet masks define the network boundary—here, both masks are 255.255.255.0, so the third octet (1 vs. 2) clearly separates them. A helpful memory tip: “Switches stay local, routers roam global.”
220-1101 IP Addressing Practice Question
This 220-1201 practice question tests your understanding of ip addressing. 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 a network where two computers cannot communicate. Computer A has an IP of 192.168.1.10 with subnet mask 255.255.255.0. Computer B has an IP of 192.168.2.20 with subnet mask 255.255.255.0. Both are connected to the same switch. The switch is not configured with VLANs. Why can't the computers communicate?
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
The computers are on different subnets and need a router to communicate.
Even though both computers are on the same physical switch, they are on different logical subnets (192.168.1.0/24 and 192.168.2.0/24). Without a router to forward traffic between subnets, they cannot communicate directly.
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The switch is blocking the traffic due to MAC address filtering.
Why it's wrong here
MAC filtering would block specific devices, but it would not explain why two devices on different subnets cannot communicate.
- ✓
The computers are on different subnets and need a router to communicate.
Why this is correct
Computers on different subnets cannot communicate directly; they require a router to forward packets between the subnets.
Related concept
Access ports place end devices into a single VLAN.
- ✗
The subnet mask on Computer B is incorrect.
Why it's wrong here
The subnet mask is correct for its own subnet (255.255.255.0), but the problem is that they are on different subnets.
- ✗
The default gateway on both computers is not set.
Why it's wrong here
A default gateway is needed to reach other subnets, but even if set, it would not enable direct communication without a router.
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
- Access ports place end devices into a single VLAN.
- Trunk ports carry multiple VLANs between switches.
- Allowed VLAN lists decide which VLANs can cross a trunk.
- Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
- Use show vlan brief to verify access VLANs.
- Use show interfaces trunk to verify trunk state and allowed VLANs.
- Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 220-1201 questions on switching, trunking, and access-port configuration.
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FAQ
Questions learners often ask
What does this 220-1201 question test?
IP Addressing — This question tests IP Addressing — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: The computers are on different subnets and need a router to communicate. — Even though both computers are on the same physical switch, they are on different logical subnets (192.168.1.0/24 and 192.168.2.0/24). Without a router to forward traffic between subnets, they cannot communicate directly.
What should I do if I get this 220-1201 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 220-1201 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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Same concept, more angles
1 more ways this is tested on 220-1201
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. A technician is configuring a new printer on a network with the IP 172.16.0.50 and subnet mask 255.255.0.0. The router's LAN IP is 172.16.0.1. A workstation with IP 172.16.1.10 can ping the printer, but a workstation with IP 172.17.0.10 cannot. What is the most likely reason?
medium- A.The printer's subnet mask is wrong.
- ✓ B.The workstation with IP 172.17.0.10 is on a different network and needs a router to reach the printer.
- C.The printer has a duplicate IP address.
- D.The default gateway on the printer is missing.
Why B: The subnet mask 255.255.0.0 means the network is 172.16.0.0/16, so 172.16.1.10 is on the same network, but 172.17.0.10 is on a different network (172.17.0.0/16). Without a router between them, they cannot communicate. This tests understanding of subnetting and how the subnet mask defines the network boundary.
Last reviewed: Jun 18, 2026
This 220-1201 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 220-1201 exam.
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