LPIC-2 Advanced Networking Configuration Practice Question
A network administrator notices that a Linux router with two network interfaces is not forwarding packets between them, despite having IP forwarding enabled in the kernel. The administrator has verified that the firewall rules are not blocking the traffic. What is the most likely cause of the issue?
⚠ Common exam trap
Candidates often assume IP forwarding alone is sufficient for routing, overlooking that the kernel still needs a routing table entry to determine the next hop, and they may confuse a missing default gateway with a firewall or ARP issue.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The default gateway on the router is not set correctly.
A Linux router needs a default gateway to forward packets to networks not directly connected to any of its interfaces. Even with IP forwarding enabled and no firewall blocking, if the default gateway is not set or is incorrect, the router will drop packets destined for remote networks. The administrator has verified that firewall rules are not blocking traffic, and ARP cache issues would not cause persistent failure, so the most likely cause is a missing or incorrectly configured default gateway.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The ARP cache on the router is stale.
Why it's wrong here
ARP cache staleness would cause connectivity issues but not prevent forwarding entirely.
- ✓
The default gateway on the router is not set correctly.
Why this is correct
If the router does not have a correct default gateway, it may not know where to send packets destined for other networks.
- ✗
The iptables FORWARD chain policy is set to DROP.
Why it's wrong here
The administrator verified firewall rules are not blocking traffic.
- ✗
The routing table does not contain a route for the destination network.
Why it's wrong here
The router can still forward packets if it has a default route or specific routes; missing routes would cause unreachability, not lack of forwarding.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LPIC-2 practice question is part of Courseiva's free LPI 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 LPIC-2 exam.