LPIC-2 Advanced Networking Configuration Practice Question
Which TWO conditions must be met for a Linux bridge to forward Ethernet frames between its ports?
⚠ Common exam trap
Test-takers frequently assume a bridge needs an IP address to forward frames (Option D), confusing Layer 2 bridging with Layer 3 routing, or they think iptables must permit traffic (Option A) due to common firewall configurations on routers.
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 bridge must be in the 'up' state
A Linux bridge must be in the 'up' administrative state (set via `ip link set br0 up`) to forward frames. Without the 'up' state, the bridge will not process or forward any Ethernet frames between its ports, regardless of other configurations.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Traffic must be allowed by iptables FORWARD chain
Why it's wrong here
iptables rules in the FORWARD chain can filter but are not required for forwarding.
- ✓
The bridge must be in the 'up' state
Why this is correct
The bridge interface must be administratively up to forward frames.
- ✓
At least two ports must be added to the bridge
Why this is correct
A bridge with only one port cannot forward frames; it needs at least two to forward between them.
- ✗
The bridge must have an IP address configured
Why it's wrong here
An IP address is not required for bridging; the bridge can be purely layer 2.
- ✗
Spanning tree must be disabled
Why it's wrong here
STP can be enabled and still allow forwarding (after convergence).
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JA
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.