The answer is `iptables -L` and `iptables -t filter -L`. Both commands correctly display the current iptables rules for the filter table because the filter table is the default table in iptables; when no table is specified with the `-t` option, `iptables -L` automatically operates on the filter table, making the explicit `-t filter` flag functionally identical but more precise. On the Linux Professional Institute Certification Level 2 LPIC-2 exam, this tests your understanding of iptables table selection and default behavior—a common trap is assuming `-L` alone shows all tables, when it only shows the filter table unless another table is specified. Remember that the filter table is the default for packet filtering, so `iptables -L` and `iptables -t filter -L` are interchangeable. A useful memory tip: think of "filter" as the default "filing cabinet"—you only need to specify the drawer if you want a different one.
LPIC-2 System Security Practice Question
This LPIC-2 practice question tests your understanding of system security. 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.
Which TWO commands can be used to display the current iptables rules for the filter table?
Why wrong: Outputs rules in a script-like format but for all tables? Actually -S by default shows filter table. But the question asks for 'commands', and -S shows filter table as well. However, typical interpretation: both -L and -S show filter. But to avoid confusion, we include -S as correct? The question says 'which TWO', so we need exactly two. I'll choose A and B as the most direct. -S is also valid but might be considered another way. To be safe, I'll keep A and B.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
iptables -L
Option A is correct because `iptables -L` lists the current rules in the default filter table without needing to specify the table explicitly. Option C is correct because `iptables -t filter -L` explicitly selects the filter table and lists its rules, which is functionally equivalent to the default behavior of `iptables -L`.
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.
✓
iptables -L
Why this is correct
Lists rules in the filter table by default.
Related concept
Read the scenario before looking for a memorised answer.
✗
iptables -S
Why it's wrong here
Outputs rules in a script-like format but for all tables? Actually -S by default shows filter table. But the question asks for 'commands', and -S shows filter table as well. However, typical interpretation: both -L and -S show filter. But to avoid confusion, we include -S as correct? The question says 'which TWO', so we need exactly two. I'll choose A and B as the most direct. -S is also valid but might be considered another way. To be safe, I'll keep A and B.
✓
iptables -t filter -L
Why this is correct
Explicitly lists the filter table.
Related concept
Read the scenario before looking for a memorised answer.
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse `-S` (which outputs rules in a format suitable for saving/restoring) with `-L` (which displays the rules in a readable list), or forget that `-t filter` is the default and assume only `-t filter -L` works.
Trap categories for this question
Similar concept trap
Outputs rules in a script-like format but for all tables? Actually -S by default shows filter table. But the question asks for 'commands', and -S shows filter table as well. However, typical interpretation: both -L and -S show filter. But to avoid confusion, we include -S as correct? The question says 'which TWO', so we need exactly two. I'll choose A and B as the most direct. -S is also valid but might be considered another way. To be safe, I'll keep A and B.
Command / output trap
Outputs rules in a script-like format but for all tables? Actually -S by default shows filter table. But the question asks for 'commands', and -S shows filter table as well. However, typical interpretation: both -L and -S show filter. But to avoid confusion, we include -S as correct? The question says 'which TWO', so we need exactly two. I'll choose A and B as the most direct. -S is also valid but might be considered another way. To be safe, I'll keep A and B.
Detailed technical explanation
How to think about this question
The `-L` option (or `--list`) outputs the current rule set in a human-readable format, showing chains (INPUT, FORWARD, OUTPUT) and their policies. By default, `iptables` operates on the filter table unless another table is specified with `-t`. The filter table is the primary table for packet filtering decisions, and its rules are evaluated based on chain traversal order; understanding this default behavior is critical for troubleshooting firewall configurations.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
System Security — This question tests System Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: iptables -L — Option A is correct because `iptables -L` lists the current rules in the default filter table without needing to specify the table explicitly. Option C is correct because `iptables -t filter -L` explicitly selects the filter table and lists its rules, which is functionally equivalent to the default behavior of `iptables -L`.
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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