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
Router1 configuration:
interface FastEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip route 0.0.0.0 0.0.0.0 10.0.0.1
Switch1: VLAN1, IP 192.168.1.2/24
PC1: IP 192.168.1.10/24, gateway 192.168.1.1
PC2: IP 192.168.2.10/24, gateway 192.168.2.1
Refer to the exhibit. PC1 (192.168.1.10) cannot communicate with PC2 (192.168.2.10). 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.
Router1 configuration:
interface FastEthernet0/0
ip address 192.168.1.1 255.255.255.0
ip route 0.0.0.0 0.0.0.0 10.0.0.1
Switch1: VLAN1, IP 192.168.1.2/24
PC1: IP 192.168.1.10/24, gateway 192.168.1.1
PC2: IP 192.168.2.10/24, gateway 192.168.2.1
A
PC2 has an incorrect default gateway
Why wrong: PC2's gateway is 192.168.2.1, which is correct for its subnet (assuming a router exists for that subnet).
B
Router1 lacks a route to the 192.168.2.0/24 network
Without a route to the 192.168.2.0 network, Router1 cannot forward packets to PC2.
C
Switch1 is not routing between VLANs
Why wrong: Switch1 is a switch, not a router, and is not capable of routing between VLANs unless configured as a layer 3 switch, which is not indicated.
D
PC1 has an incorrect subnet mask
Why wrong: PC1 uses /24, which matches its subnet; the mask is correct.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Router1 lacks a route to the 192.168.2.0/24 network
Router1 lacks a route to the 192.168.2.0/24 network, so when PC1 sends traffic to PC2, Router1 does not have a destination network entry in its routing table to forward the packets. Without a route, the router drops the packets and may send an ICMP Destination Unreachable message back to PC1. This is the most likely cause because PC1 can reach its default gateway (Router1), but Router1 cannot forward traffic to the remote 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.
✗
PC2 has an incorrect default gateway
Why it's wrong here
PC2's gateway is 192.168.2.1, which is correct for its subnet (assuming a router exists for that subnet).
✓
Router1 lacks a route to the 192.168.2.0/24 network
Why this is correct
Without a route to the 192.168.2.0 network, Router1 cannot forward packets to PC2.
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.
✗
Switch1 is not routing between VLANs
Why it's wrong here
Switch1 is a switch, not a router, and is not capable of routing between VLANs unless configured as a layer 3 switch, which is not indicated.
✗
PC1 has an incorrect subnet mask
Why it's wrong here
PC1 uses /24, which matches its subnet; the mask is correct.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a router automatically knows all networks in a topology, but routers only know directly connected networks unless routes are explicitly configured or learned via a routing protocol.
Detailed technical explanation
How to think about this question
Routers maintain a routing table with entries for directly connected networks and static or dynamic routes. When a packet arrives destined for a non-local network, the router performs a longest-prefix match lookup; if no match is found, the packet is discarded. In real-world scenarios, missing routes are often due to misconfigured static routes or incomplete dynamic routing protocol adjacencies (e.g., OSPF, EIGRP).
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Infrastructure — This question tests Infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Router1 lacks a route to the 192.168.2.0/24 network — Router1 lacks a route to the 192.168.2.0/24 network, so when PC1 sends traffic to PC2, Router1 does not have a destination network entry in its routing table to forward the packets. Without a route, the router drops the packets and may send an ICMP Destination Unreachable message back to PC1. This is the most likely cause because PC1 can reach its default gateway (Router1), but Router1 cannot forward traffic to the remote subnet.
What should I do if I get this FC0-U61 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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Question Discussion
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