JN0-106 Practice Question: IRB (Integrated Routing and Bridging) Interface
An engineer is troubleshooting a network issue where hosts on the same VLAN cannot communicate with each other. Which configuration element is most likely missing?
⚠ Common exam trap
Many exam-takers confuse the need for a default gateway (Layer 3) with Layer 2 connectivity, assuming hosts on the same VLAN need a gateway to communicate, when in fact they communicate directly via ARP and MAC addresses.
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
✓
Spanning Tree Protocol enabled
Hosts on the same VLAN communicate at Layer 2 and do not require any Layer 3 configuration such as an IRB interface or default gateway. The most likely missing configuration is that Spanning Tree Protocol (STP) is not enabled. Without STP, loops can cause broadcast storms and MAC address flapping, preventing communication between hosts in the same VLAN. Therefore, option A is correct.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Spanning Tree Protocol enabled
Why this is correct
STP prevents loops, does not affect Layer 3 connectivity.
- ✗
An IRB interface for the VLAN
Why it's wrong here
An IRB interface provides Layer 3 functionality for a VLAN on MX or EX series.
- ✗
A Layer 3 switchport
Why it's wrong here
Layer 3 switchports are for routed ports, not VLAN interfaces.
- ✗
A default gateway for the VLAN
Why it's wrong here
Default gateway is for inter-VLAN communication, not intra-VLAN.
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 JN0-106 practice question is part of Courseiva's free Juniper Networks 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 JN0-106 exam.