LFCS Networking Practice Question
Which THREE conditions must be met for a Linux system to function as a router between two networks?
⚠ Common exam trap
Watch out — candidates often think a router must be the default gateway for both networks, but in reality, it only needs to have IP addresses in each subnet and proper routing entries; the default gateway is a client-side setting, not a router requirement.
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
✓
Each interface has an IP address in the respective subnet
Each interface must have an IP address in its respective subnet for the Linux system to receive packets from that network and forward them to the other. Without an IP address in the subnet, the interface cannot participate in ARP resolution or routing decisions for that network.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Each interface has an IP address in the respective subnet
Why this is correct
The router must have an IP in each network to send/receive packets.
- ✓
IP forwarding is enabled (net.ipv4.ip_forward = 1)
Why this is correct
This is required to forward packets between interfaces.
- ✗
Both interfaces have the same MAC address
Why it's wrong here
Interfaces must have unique MAC addresses.
- ✓
iptables rules allow forwarding (FORWARD chain policy or rules)
Why this is correct
Firewall rules must permit packet forwarding.
- ✗
The system is configured as the default gateway for both networks
Why it's wrong here
The system can act as a router without being the default gateway.
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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.