The answer is that a firewall on PC2 is blocking ICMP echo requests, which is the most likely reason PC1 cannot ping PC2. This occurs because firewalls can be configured to filter specific types of traffic, and ICMP (the protocol used by ping) is often restricted for security reasons while allowing other communications like web or file transfers. On the CompTIA ITF+ FC0-U61 exam, this scenario tests your understanding of how firewalls operate at the host level versus network-level issues, and it frequently appears as a trap where students mistakenly blame a faulty switch port or missing default gateway. Remember that if PC1 can ping PC3 on the same subnet, the network infrastructure is fine, so the problem must be specific to PC2’s configuration. A useful memory tip: “Ping is optional, not essential—firewalls often block the echo, not the connection.”
FC0-U61 Infrastructure Practice Question
This FC0-U61 practice question tests your understanding of infrastructure. 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.
Exhibit
Refer to the exhibit.
Router LAN IP: 192.168.1.1/24
Switch: Unmanaged
PC1: IP 192.168.1.10/24
PC2: IP 192.168.1.11/24
PC3: IP 192.168.1.12/24
All devices are connected and powered on. PC1 can ping PC3 but cannot ping PC2.
What is the most likely reason PC1 cannot ping PC2?
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.
Refer to the exhibit.
Router LAN IP: 192.168.1.1/24
Switch: Unmanaged
PC1: IP 192.168.1.10/24
PC2: IP 192.168.1.11/24
PC3: IP 192.168.1.12/24
All devices are connected and powered on. PC1 can ping PC3 but cannot ping PC2.
A
The default gateway is incorrect on PC1
Why wrong: Default gateway is not used for same-subnet communication.
B
A firewall on PC2 is blocking ICMP echo requests
Firewalls often block ping by default while allowing other traffic.
C
PC2's network interface is disabled
Why wrong: A disabled NIC would cause complete loss of connectivity, not just ping failure.
D
The switch port for PC2 is faulty
Why wrong: A faulty switch port would disrupt all traffic to PC2, not just ping.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A firewall on PC2 is blocking ICMP echo requests
Option C is correct because a firewall on PC2 can be configured to block ICMP echo requests (ping) while allowing other traffic. Option A is incorrect because if PC2's NIC were disabled, PC1 would not be able to communicate with PC2 at all, and the ping would fail, but it's not the most likely scenario given that PC1 can ping PC3 (indicating the switch and network are functioning). Option B is incorrect because a default gateway is only required for off-subnet communication; PC1 and PC2 are on the same subnet. Option D is incorrect because if the switch port for PC2 were faulty, PC2 would have no network connectivity, and PC1 would fail to reach it for any service, not just ping.
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.
A disabled NIC would cause complete loss of connectivity, not just ping failure.
✗
The switch port for PC2 is faulty
Why it's wrong here
A faulty switch port would disrupt all traffic to PC2, not just ping.
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.
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.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related FC0-U61 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure — This question tests Infrastructure — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: A firewall on PC2 is blocking ICMP echo requests — Option C is correct because a firewall on PC2 can be configured to block ICMP echo requests (ping) while allowing other traffic. Option A is incorrect because if PC2's NIC were disabled, PC1 would not be able to communicate with PC2 at all, and the ping would fail, but it's not the most likely scenario given that PC1 can ping PC3 (indicating the switch and network are functioning). Option B is incorrect because a default gateway is only required for off-subnet communication; PC1 and PC2 are on the same subnet. Option D is incorrect because if the switch port for PC2 were faulty, PC2 would have no network connectivity, and PC1 would fail to reach it for any service, not just ping.
What should I do if I get this FC0-U61 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 FC0-U61 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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