LPIC-1 Essential System Services and Networking Practice Question
This LPIC-1 practice question tests your understanding of essential system services and networking. 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.
After running 'ip route show default', a system administrator sees no output. Users on that system can only communicate with hosts on the local subnet. 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 default gateway is missing
Option B is correct because the absence of a default route means traffic to destinations outside the local subnet cannot be forwarded. Option A could be an issue but connectivity to local subnet works. Option C is less specific, and Option D would cause no connectivity at all.
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.
✗
DNS is misconfigured
Why it's wrong here
DNS issues would not prevent IP communication to non-local hosts if route exists.
✗
A firewall is blocking all traffic
Why it's wrong here
A firewall might block specific traffic, but local subnet works.
✗
The network interface is down
Why it's wrong here
If the interface were down, local subnet would not work either.
✓
The default gateway is missing
Why this is correct
Without a default route, traffic cannot reach external networks.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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 LPIC-1 subnetting questions on CIDR, address ranges, and subnet selection.
Essential System Services and Networking — This question tests Essential System Services and Networking — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The default gateway is missing — Option B is correct because the absence of a default route means traffic to destinations outside the local subnet cannot be forwarded. Option A could be an issue but connectivity to local subnet works. Option C is less specific, and Option D would cause no connectivity at all.
What should I do if I get this LPIC-1 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 LPIC-1 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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Question Discussion
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