LPIC-2 Advanced Networking Configuration Practice Question
An administrator configures a bridge br0 with two ports (eth0 and eth1). The network uses STP. After configuration, packets from a host on eth0 to a host on eth1 are not forwarded. The bridge shows blocking state for one of the ports. What is the most likely cause?
⚠ Common exam trap
Candidates often think STP only blocks ports when there are multiple switches in a loop, but STP also blocks ports on a single bridge with two ports in the same broadcast domain because it sees a loop between its own ports.
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 has loop detection and blocked one port
The bridge br0 has two ports (eth0 and eth1) and STP is enabled. STP detects a loop in the network — in this case, the bridge itself with two ports on the same broadcast domain creates a loop. To prevent broadcast storms and MAC table instability, STP places one of the ports into the blocking state, which stops forwarding frames between the two ports. This is why packets from a host on eth0 to a host on eth1 are not forwarded.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Incorrect MTU
Why it's wrong here
MTU mismatch may cause fragmentation issues, not blocking state.
- ✗
STP is disabled
Why it's wrong here
If STP disabled, both ports would be forwarding, so not cause of blocking.
- ✗
MAC address learning is disabled
Why it's wrong here
Disabling learning would flood packets but not cause STP blocking.
- ✗
The bridge is in promiscuous mode
Why it's wrong here
Promiscuous mode affects packet capture, not blocking state.
- ✓
The bridge has loop detection and blocked one port
Why this is correct
STP blocks redundant paths to prevent loops, which can cause one port to be in blocking state.
Visual reference
Quick reference
Access Control Model Comparison
| Model | Acronym | Who Controls Access? | Best For |
|---|---|---|---|
| Discretionary Access Control | DAC | Resource owner | Small teams, file shares |
| Mandatory Access Control | MAC | System / security labels | Classified govt / military |
| Role-Based Access Control | RBAC | Administrator (via roles) | Enterprise environments |
| Attribute-Based Access Control | ABAC | Policy engine (user + resource attributes) | Fine-grained, dynamic policies |
| Rule-Based Access Control | RuBAC | System rules / ACLs | Firewall rules, network ACLs |
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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.