JNCIS-ENT Spanning Tree Practice Question
An organization runs MSTP with multiple instances. A packet belonging to a VLAN that is not explicitly mapped to any MST instance is processed in which manner?
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
✓
It is automatically mapped to Instance 0 (the CIST).
Any unmapped VLANs in MSTP are automatically mapped to Instance 0, which is the CIST (Common and Internal Spanning Tree).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
It is processed by the default RSTP instance running outside MSTP.
Why it's wrong here
MSTP replaces RSTP entirely within the region; unmapped VLANs go to Instance 0.
- ✗
It is dropped by the switch because unmapped VLANs are considered invalid in MSTP.
Why it's wrong here
Unmapped VLANs are not dropped; they fall back to Instance 0.
- ✓
It is automatically mapped to Instance 0 (the CIST).
Why this is correct
Instance 0 acts as the default catch-all instance for any unmapped VLANs.
- ✗
It floods to all ports regardless of spanning tree port states.
Why it's wrong here
Spanning tree states apply fully to Instance 0 for unmapped VLANs.
Visual reference
About these practice questions
This JNCIS-ENT question is part of Courseiva's 506-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed August 2026 · checked against the official Juniper Networks exam blueprint
This JNCIS-ENT 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 JNCIS-ENT exam.