LPIC-2 Advanced Networking Configuration Practice Question
This LPIC-2 practice question tests your understanding of advanced networking configuration. 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.
An administrator wants to allow SSH access from the internal network (192.168.1.0/24) only, using nftables. Which rule should be added to the filter table input chain?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
iif lo accept; tcp dport 22 ip saddr 192.168.1.0/24 accept
Option C is correct because it first accepts loopback traffic (iif lo accept) to avoid breaking local services, then uses a combined match: tcp dport 22 ip saddr 192.168.1.0/24 accept. This ensures only SSH packets from the 192.168.1.0/24 subnet are accepted, while all other SSH attempts are implicitly dropped by the default policy (typically drop) of the input chain. The rule syntax follows nftables' concise, single-line format without semicolons or comments.
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.
✗
tcp dport 22 accept #from 192.168.1.0/24
Why it's wrong here
The comment is not a source condition; the rule accepts SSH from anywhere.
✗
tcp dport 22 accept; ip saddr 192.168.1.0/22 accept
Why it's wrong here
First rule accepts all SSH; second rule with wrong netmask does nothing useful.
✓
iif lo accept; tcp dport 22 ip saddr 192.168.1.0/24 accept
Why this is correct
Accepts loopback traffic and SSH from the specified subnet.
Related concept
Read the scenario before looking for a memorised answer.
✗
tcp dport 22 ip saddr != 192.168.1.0/24 drop
Why it's wrong here
Drops SSH from non-matching sources but requires a default accept for other traffic, which may not be desired.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse nftables syntax with iptables or think that a comment or semicolon can be used to add conditions, when in fact nftables requires explicit, comma-separated matches within a single rule statement.
Detailed technical explanation
How to think about this question
In nftables, rules are evaluated sequentially within a chain, and the default policy (often 'drop' for input) applies if no rule matches. The 'iif lo accept' rule is critical to prevent locking out local services (e.g., SSH from localhost) and to avoid dropping packets from the loopback interface. The combined match 'tcp dport 22 ip saddr 192.168.1.0/24 accept' uses a single rule with multiple selectors, which is more efficient than separate rules and ensures atomic evaluation; nftables does not support inline comments as match criteria, unlike iptables.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Advanced Networking Configuration — This question tests Advanced Networking Configuration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: iif lo accept; tcp dport 22 ip saddr 192.168.1.0/24 accept — Option C is correct because it first accepts loopback traffic (iif lo accept) to avoid breaking local services, then uses a combined match: tcp dport 22 ip saddr 192.168.1.0/24 accept. This ensures only SSH packets from the 192.168.1.0/24 subnet are accepted, while all other SSH attempts are implicitly dropped by the default policy (typically drop) of the input chain. The rule syntax follows nftables' concise, single-line format without semicolons or comments.
What should I do if I get this LPIC-2 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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