JN0-106 Junos OS Fundamentals Practice Question
Your data center uses Juniper QFX5110 switches as leaf nodes in a Virtual Chassis Fabric (VCF) topology with QFX5100 as spine nodes. You are adding a new QFX5110 leaf node to the fabric. The new switch is physically connected to all spine nodes as per the cabling guidelines. However, after powering on the new switch, it does not automatically join the fabric. The existing fabric shows the new switch's member ID as 8, but it remains in 'standalone' state. The VCF has been operational for several months without issues. You check the configuration on the existing VC and notice that the 'virtual-chassis' configuration does not include the new member. What is the most likely reason the new switch does not join?
⚠ Common exam trap
Many exam-takers assume a switch with a member ID assigned has successfully joined the fabric, but in VCF, member ID assignment happens early in the discovery process and does not guarantee full integration—the switch must also have a matching virtual-chassis ID to move out of 'standalone' state.
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 new switch does not have the same virtual-chassis ID configured as the existing fabric
In a Virtual Chassis Fabric (VCF), all member switches must share the same virtual-chassis ID to be recognized as part of the same fabric. The existing fabric has a configured virtual-chassis ID, but the new QFX5110, by default, has a different or no virtual-chassis ID set. Without a matching virtual-chassis ID, the new switch cannot join the fabric and remains in 'standalone' state, even though it is physically connected and assigned a member ID.
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 new switch is running a different version of Junos that is not compatible with the fabric
Why it's wrong here
While Junos version compatibility is essential for VCF formation, the scenario does not indicate any version discrepancy. The QFX5110 supports the same major Junos releases as other VCF-capable switches, and a version mismatch would typically cause an explicit error or prevent the member identification, but the question does not state this as the cause. Therefore, this is an incorrect diagnosis.
- ✓
The new switch does not have the same virtual-chassis ID configured as the existing fabric
Why this is correct
In a Juniper Virtual Chassis Fabric, every member must share the same virtual-chassis ID (VC-ID) to be recognized as part of the fabric. If the new leaf's VC-ID differs, it will not accept member-add requests and will remain isolated even though physically connected. The VC-ID is typically configured at initial provisioning, and mismatches manifest as the device failing to join the fabric.
- ✗
The new switch is only connected to one spine node, and VCF requires full mesh connections to all spines
Why it's wrong here
A VCF leaf node only needs at least one connection to a spine node to be discovered and participate in fabric operations. The VCF topology recommends full mesh for redundancy and performance, but it is not a hard requirement for membership. The device will still join and exchange fabric membership information over the single link, so this option incorrectly states a requirement.
- ✗
The new switch has 'set virtual-chassis no-split-detection' enabled, preventing it from joining
Why it's wrong here
The 'no-split-detection' configuration is designed to control the behavior when a virtual chassis splits (i.e., when member links are lost), ensuring that certain members remain active. It does not influence the process of a new device joining the fabric. A leaf with this setting enabled can still join a VCF as long as its VC-ID and version are compatible; therefore, this is not the cause.
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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.