JNCIP-ENT Ethernet Switching And Spanning Tree Practice Question
When configuring advanced Layer 2 tunneling (Q-in-Q) on Juniper EX Series switches, which THREE statements are correct regarding VLAN stacking behavior and limitations? (Choose three)
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
✓
MTU sizes across the core must be adjusted to account for the extra 4 bytes of the added outer VLAN tag.
QinQ on Juniper EX switches involves specific encapsulation requirements like flexible-ethernet-services, stacking VLAN tags on ingress and popping on egress, and preserving inner customer VLAN tags transparently.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Layer 2 Protocol Tunneling (L2PT) is automatically enabled for all protocols without additional configuration when QinQ is active.
Why it's wrong here
L2PT must be explicitly configured on customer-facing access/tunnel ports to process and tunnel control traffic like BPDUs or CDP.
- ✓
MTU sizes across the core must be adjusted to account for the extra 4 bytes of the added outer VLAN tag.
Why this is correct
Because stacked tags add overhead (an extra 4 bytes per tag), core link MTU must be increased to prevent frame fragmentation or drops.
- ✓
Incoming customer frames have an outer VLAN tag pushed onto them at the provider edge ingress port.
Why this is correct
The provider edge switch pushes a service provider outer VLAN tag onto the incoming customer frame.
- ✓
The inner customer VLAN tags remain entirely untouched and transparent as the frames traverse the provider core.
Why this is correct
Customer inner VLAN tags pass through the provider core transparently without modification.
- ✗
QinQ tunneling requires standard access mode encapsulation on all core-facing uplink ports.
Why it's wrong here
Core-facing uplink ports typically use trunk mode encapsulation carrying the stacked provider VLANs.
Visual reference
About these practice questions
Courseiva writes every JNCIP-ENT question from scratch — 336 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or 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 JNCIP-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 JNCIP-ENT exam.