The correct command is `ip route add 172.16.0.0/16 via 10.0.0.5 dev eth1`, because the VPN tunnel endpoint at 10.0.0.5 on the eth1 subnet acts as the next-hop gateway for reaching the remote 172.16.0.0/16 network. This command explicitly tells the kernel to forward all traffic destined for that remote range through the 10.0.0.5 gateway, using the eth1 interface as the egress path. On the Linux Foundation Certified System Administrator LFCS exam, this scenario tests your understanding of policy routing with multiple interfaces and the distinction between directly connected routes and static routes via a gateway. A common trap is to mistakenly use the server’s own IP or the default gateway as the next-hop; remember that the `via` address must be a reachable IP on the same subnet as the chosen interface. For a memory tip, think “VPN via VPN’s IP” — the next-hop is always the tunnel endpoint, not your own interface address.
LFCS Networking Practice Question
This LFCS practice question tests your understanding of networking. 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.
A company has a server with two network interfaces: eth0 (192.168.1.10/24, gateway 192.168.1.1) and eth1 (10.0.0.10/24, gateway 10.0.0.1). The server needs to reach a remote network 172.16.0.0/16 via a VPN tunnel that terminates at 10.0.0.5 on eth1. Which command should be used to add a route for this traffic?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ip route add 172.16.0.0/16 via 10.0.0.5 dev eth1
Option A is correct because the VPN tunnel endpoint is at 10.0.0.5 on the eth1 network, so traffic to 172.16.0.0/16 must be forwarded via that next-hop IP address using the eth1 interface. The `ip route add` command with `via 10.0.0.5 dev eth1` explicitly sets the gateway and egress interface, ensuring packets are sent through the VPN tunnel.
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.
✓
ip route add 172.16.0.0/16 via 10.0.0.5 dev eth1
Why this is correct
This correctly routes traffic to the VPN endpoint via eth1.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
ip route add 172.16.0.0/16 via 10.0.0.5 dev eth0
Why it's wrong here
This specifies eth0, but the VPN endpoint is reachable via eth1.
✗
ip route add 172.16.0.0/16 via 192.168.1.1 dev eth0
Why it's wrong here
This route sends traffic via the default gateway on eth0, bypassing the VPN.
✗
ip route add 172.16.0.0/16 dev eth1
Why it's wrong here
This assumes the network is directly connected, which it is not.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often forget to specify the `via` next-hop IP when the destination is not directly connected, or they mistakenly use the default gateway instead of the VPN tunnel endpoint, assuming all external traffic goes through the same gateway.
Detailed technical explanation
How to think about this question
The `ip route add` command manipulates the kernel's routing table (FIB). When a `via` address is specified, the kernel performs a recursive route lookup to resolve the next-hop; if the next-hop is on a directly connected subnet (like 10.0.0.5 on eth1), the route is installed as a gateway route. In real-world VPN scenarios, the tunnel interface (e.g., tun0) often replaces the physical interface in the route, but here the VPN terminates at a remote IP, so the physical interface must be used to reach the tunnel endpoint.
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.
Networking — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: ip route add 172.16.0.0/16 via 10.0.0.5 dev eth1 — Option A is correct because the VPN tunnel endpoint is at 10.0.0.5 on the eth1 network, so traffic to 172.16.0.0/16 must be forwarded via that next-hop IP address using the eth1 interface. The `ip route add` command with `via 10.0.0.5 dev eth1` explicitly sets the gateway and egress interface, ensuring packets are sent through the VPN tunnel.
What should I do if I get this LFCS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
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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