JNCIS-ENT Spanning Tree Practice Question
An operator configures RSTP across multiple EX Series switches. A rogue switch running legacy STP is connected to an RSTP switch. How does the RSTP switch handle interaction with the legacy STP switch?
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 RSTP switch falls back to legacy STP behavior on that specific interface.
RSTP switches have a migration mechanism that automatically detects legacy STP BPDUs on a per-port basis and falls back to running legacy 802.1D STP behavior on that specific port.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The port receiving legacy BPDUs is immediately placed into a permanent error-disabled state.
Why it's wrong here
Interoperability mechanisms prevent immediate error-disabling by falling back to legacy STP.
- ✗
The legacy STP BPDUs are dropped and logged as protocol violations.
Why it's wrong here
They are processed using the migration protocol mechanism rather than being dropped as violations.
- ✗
The entire switch converts its spanning tree mode to legacy STP.
Why it's wrong here
Fallback happens on a per-port basis, not globally across the entire switch.
- ✓
The RSTP switch falls back to legacy STP behavior on that specific interface.
Why this is correct
Per-port protocol migration allows interoperability by downgrading to 802.1D on ports receiving legacy BPDUs.
Visual reference
About these practice questions
This JNCIS-ENT question is part of Courseiva's 519-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.