LPIC-1 Essential System Services and Networking Practice Question
This LPIC-1 practice question tests your understanding of essential system services and networking. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 security administrator needs to allow SSH access from the 10.0.0.0/8 network but deny all other traffic to port 22. The firewall uses iptables with default policy ACCEPT on the INPUT chain. Which set of rules should be added?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
iptables -A INPUT -s 10.0.0.0/8 -p tcp --dport 22 -j ACCEPT; iptables -A INPUT -p tcp --dport 22 -j DROP
Option C is correct: First rule allows SSH from 10.0.0.0/8, second rule drops all other SSH. Option A would drop all SSH. Option B allows from subnet but doesn't block others. Option D blocks subnet.
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.
✗
iptables -A INPUT -p tcp --dport 22 -j DROP; iptables -A INPUT -s 10.0.0.0/8 -p tcp --dport 22 -j ACCEPT
Why it's wrong here
Order matters; drop rule blocks all SSH before allow.
✗
iptables -A INPUT -s 10.0.0.0/8 -p tcp --dport 22 -j DROP; iptables -A INPUT -p tcp --dport 22 -j ACCEPT
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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: iptables -A INPUT -s 10.0.0.0/8 -p tcp --dport 22 -j ACCEPT; iptables -A INPUT -p tcp --dport 22 -j DROP — Option C is correct: First rule allows SSH from 10.0.0.0/8, second rule drops all other SSH. Option A would drop all SSH. Option B allows from subnet but doesn't block others. Option D blocks subnet.
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.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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