LFCS Networking Practice Question
You are troubleshooting a Linux server that acts as a router between two networks: 10.0.1.0/24 (eth0) and 10.0.2.0/24 (eth1). IP forwarding is enabled. Hosts on 10.0.1.0/24 can ping the server's eth0 IP (10.0.1.1), but cannot ping hosts on 10.0.2.0/24 (e.g., 10.0.2.10). The server can ping both 10.0.2.10 and 10.0.1.10. The iptables FORWARD chain policy is ACCEPT. What is the most likely cause?
⚠ Common exam trap
Test-takers frequently assume the router's IP forwarding or firewall is the problem when the server itself can reach both networks, overlooking the requirement for client-side routing configuration.
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 hosts on 10.0.1.0/24 do not have a route to 10.0.2.0/24
The server can ping both networks, confirming IP forwarding is enabled and iptables FORWARD chain policy is ACCEPT. Hosts on 10.0.1.0/24 can ping the server's eth0 IP but not hosts on 10.0.2.0/24, which indicates the hosts lack a route to the 10.0.2.0/24 network. Without a route, packets from 10.0.1.0/24 destined for 10.0.2.0/24 are dropped at the source host because the kernel has no next-hop information for that destination.
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 hosts on 10.0.1.0/24 do not have a route to 10.0.2.0/24
Why this is correct
If hosts don't know where 10.0.2.0/24 is, they send packets to their default gateway, which may not be this server.
- ✗
The server cannot reach 10.0.2.10
Why it's wrong here
The server can ping 10.0.2.10.
- ✗
IP forwarding is not enabled
Why it's wrong here
The scenario states IP forwarding is enabled.
- ✗
The iptables FORWARD chain has a DROP policy
Why it's wrong here
The policy is ACCEPT.
Go deeper
Related to this question
About these practice questions
One of 507 original LFCS practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.