This LFCS practice question tests your understanding of networking. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
# ip addr show eth0
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:1a:2b:3c:4d:5e brd ff:ff:ff:ff:ff:ff
inet 192.168.10.15/24 brd 192.168.10.255 scope global dynamic eth0
valid_lft 86399sec preferred_lft 86399sec
inet6 fe80::21a:2bff:fe3c:4d5e/64 scope link
valid_lft forever preferred_lft forever
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.10.1 0.0.0.0 UG 0 0 0 eth0
192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
# ping -c 1 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
From 192.168.10.15 icmp_seq=1 Destination Host Unreachable
Based on the exhibit, a system administrator runs ping to 8.8.8.8 and gets 'Destination Host Unreachable'. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The gateway 192.168.10.1 is not reachable from this host.
The 'Destination Host Unreachable' message indicates that the host has no route to the destination network or the next-hop gateway is not reachable. Since the ping target is 8.8.8.8 (a public IP), the host must forward traffic to its default gateway. If the gateway 192.168.10.1 is not reachable (e.g., due to a down interface, ARP failure, or missing neighbor entry), the kernel will immediately return this ICMP error without attempting to send the packet.
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.
✗
The IP address 192.168.10.15 is not configured on eth0.
Why it's wrong here
The IP is configured as shown in ip addr.
✗
A firewall is blocking ICMP traffic.
Why it's wrong here
The error is 'Destination Host Unreachable', not 'Request timed out', suggesting a routing issue rather than a firewall block.
✓
The gateway 192.168.10.1 is not reachable from this host.
Why this is correct
The ping error indicates the gateway cannot be reached, likely because it's down or not on the same network.
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.
✗
The default route is missing.
Why it's wrong here
The default route is present (0.0.0.0 via 192.168.10.1).
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse 'Destination Host Unreachable' (which indicates a local routing or next-hop reachability issue) with 'Request Timed Out' (which typically indicates a remote firewall or network congestion), leading them to incorrectly select a firewall blocking ICMP.
Trap categories for this question
Command / output trap
The IP is configured as shown in ip addr.
Detailed technical explanation
How to think about this question
When a host sends a packet to a non-local destination, it checks its routing table for a matching route. If a default route exists (e.g., via 192.168.10.1), the kernel performs an ARP request for that gateway's IP on the local subnet. If no ARP reply is received (or the gateway's MAC is not in the ARP cache and the interface is down), the kernel generates an ICMP Destination Host Unreachable (Type 3, Code 1) from the local host. This differs from 'Network Unreachable' (Type 3, Code 0), which occurs when no route exists at all. In real-world scenarios, a misconfigured static route or a downed gateway interface on the router can cause this exact symptom.
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 network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
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.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The gateway 192.168.10.1 is not reachable from this host. — The 'Destination Host Unreachable' message indicates that the host has no route to the destination network or the next-hop gateway is not reachable. Since the ping target is 8.8.8.8 (a public IP), the host must forward traffic to its default gateway. If the gateway 192.168.10.1 is not reachable (e.g., due to a down interface, ARP failure, or missing neighbor entry), the kernel will immediately return this ICMP error without attempting to send the packet.
What should I do if I get this LFCS 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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