This LFCS practice question tests your understanding of networking. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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 legacy command can still be used to view the IPv4 routing table on a modern Linux system?
ip route show
Why wrong: This is the modern command, but the question asks for a legacy command.
route -n
Why wrong: route is also legacy but may not be installed by default on some distributions.
arp -a
Why wrong: This command shows the ARP table, not the routing table.
netstat -r
netstat -r is a legacy command that still works on most systems.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
netstat -r
Option D is correct because `netstat -r` is a legacy command that reads the kernel routing table from `/proc/net/route` and displays it in a human-readable format. It remains available on modern Linux systems for backward compatibility, even though its use is discouraged in favor of `ip route`. The `-r` flag specifically instructs `netstat` to show the routing table.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
ip route show
Why it's wrong here
This is the modern command, but the question asks for a legacy command.
route -n
Why it's wrong here
route is also legacy but may not be installed by default on some distributions.
arp -a
Why it's wrong here
This command shows the ARP table, not the routing table.
netstat -r
Why this is correct
netstat -r is a legacy command that still works on most systems.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse 'legacy command' with 'modern command' and pick `ip route show` (Option A) because it is the current standard, but the question explicitly asks for a legacy command that still works.
Trap categories for this question
Command / output trap
This is the modern command, but the question asks for a legacy command.
Detailed technical explanation
The kernel routing table is stored in the `fib_trie` and `fib_table` structures for IPv4, and legacy commands like `netstat -r` and `route` read from `/proc/net/route` (which is a text-based snapshot of the Forwarding Information Base). The `ip route` command uses netlink sockets (RTNETLINK) to communicate directly with the kernel, providing more detailed and dynamic information, such as multiple routing tables and policy routing. In a real-world scenario, a system administrator might use `netstat -r` on an older script or during troubleshooting on a minimal system where `iproute2` is not installed.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
The correct answer is: netstat -r — Option D is correct because `netstat -r` is a legacy command that reads the kernel routing table from `/proc/net/route` and displays it in a human-readable format. It remains available on modern Linux systems for backward compatibility, even though its use is discouraged in favor of `ip route`. The `-r` flag specifically instructs `netstat` to show the routing table.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This LFCS practice question is part of Courseiva's free Linux Foundation certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LFCS exam.
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