220-1101 Network Troubleshooting Practice Question
This 220-1201 practice question tests your understanding of network troubleshooting. 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 small office has a single switch connecting all workstations. Several users report that they cannot access the internet, but they can still communicate with each other on the local network. What is the most likely cause?
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.
Why wrong: A bad port would affect only one user, not multiple users simultaneously, and local communication would also fail for that user.
B
The router is not properly routing traffic to the internet.
If the router is down or misconfigured, local traffic within the switch works, but internet-bound traffic fails because routing is broken.
C
The DNS server is unreachable.
Why wrong: DNS failure would prevent name resolution but users could still access the internet by IP address; the scenario says no internet access at all.
D
The workstations have incorrect subnet masks.
Why wrong: Incorrect subnet masks would likely disrupt local communication as well, but users can still communicate locally.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The router is not properly routing traffic to the internet.
Local communication working while internet access fails points to a problem with the router or the connection between the switch and the router. The switch itself is functioning correctly for local traffic, so the issue is upstream.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 has a bad port.
Why it's wrong here
A bad port would affect only one user, not multiple users simultaneously, and local communication would also fail for that user.
✓
The router is not properly routing traffic to the internet.
Why this is correct
If the router is down or misconfigured, local traffic within the switch works, but internet-bound traffic fails because routing is broken.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
DNS failure would prevent name resolution but users could still access the internet by IP address; the scenario says no internet access at all.
✗
The workstations have incorrect subnet masks.
Why it's wrong here
Incorrect subnet masks would likely disrupt local communication as well, but users can still communicate locally.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Trap categories for this question
Scenario analysis trap
DNS failure would prevent name resolution but users could still access the internet by IP address; the scenario says no internet access at all.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 220-1201 question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
Network Troubleshooting — This question tests Network Troubleshooting — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The router is not properly routing traffic to the internet. — Local communication working while internet access fails points to a problem with the router or the connection between the switch and the router. The switch itself is functioning correctly for local traffic, so the issue is upstream.
What should I do if I get this 220-1201 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related 220-1201 subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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