JN0-106 Networking Fundamentals Practice Question
An engineer is implementing VLAN trunking between two Juniper EX switches. Which statement about native VLANs on a trunk is correct?
⚠ Common exam trap
Many exam-takers confuse the native VLAN behavior with Cisco's default where the native VLAN is VLAN 1 and is untagged, but they may incorrectly assume that all frames on a trunk are always tagged, leading them to select option B.
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
✓
Untagged frames arriving on a trunk port are assigned to the native VLAN.
On Juniper EX switches, a trunk port can accept both tagged and untagged frames. Untagged frames received on a trunk port are automatically assigned to the native VLAN, which by default is VLAN 1. This behavior is defined by the IEEE 802.1Q standard, where the native VLAN is the only VLAN that can carry untagged traffic on a trunk link.
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 native VLAN cannot be changed after initial configuration.
Why it's wrong here
In Junos, the native VLAN is not a permanent, immutable value: it is a per-interface setting in the ethernet-switching family configuration, and you can change it at any time with the `native-vlan` statement (e.g., `set interfaces ge-0/0/1 unit 0 family ethernet-switching native-vlan sales`). The running configuration is updated immediately and no reboot or complete trunk rebuild is required. Thus, claiming it cannot be changed after initial configuration misrepresents a simple, live-updatable parameter.
- ✗
Frames in the native VLAN are always tagged with the VLAN ID on the trunk.
Why it's wrong here
IEEE 802.1Q trunk links carry frames from multiple VLANs by adding a 4-byte tag, but each trunk is also allowed to designate one native VLAN whose frames are transmitted without any tag — and on arrival, those untagged frames are placed into that same native VLAN. Therefore, the statement that native VLAN frames are 'always tagged' directly contradicts how a native VLAN works; the entire point is to leave those frames untagged, often to interoperate with legacy devices or to support mixed-format traffic. On Junos, you explicitly configure the native VLAN to control which untagged packets are associated with which VLAN.
- ✗
The native VLAN must be the same as the management VLAN.
Why it's wrong here
The native VLAN and the management VLAN are conceptually separate: the native VLAN is a layer-2 trunk-port property that handles untagged frames, while the management VLAN is a layer-3 construct used for out-of-band or in-band management access (SSH/SNMP/CLI). On a Junos device, the management interface could be a separate routing (RE) port (like `me0`) or a VLAN with an IRB interface, and that VLAN is wholly independent of the trunk's native VLAN setting. There is no Junos requirement that the management VLAN equal the native VLAN; they are different configuration namespaces, and you can set them to any values you need.
- ✓
Untagged frames arriving on a trunk port are assigned to the native VLAN.
Why this is correct
Yes — that is the definition of the native VLAN on an IEEE 802.1Q trunk. When a port is in trunk mode and an untagged Ethernet frame arrives, the switch does not discard it; it processes that frame as if it were tagged with the configured native VLAN ID, placing it in that VLAN's forwarding database. This allows a trunk to also carry traffic from a legacy device that does not add tags, or to carry certain control protocols without us forced to use tags. In Junos, you configure this with the `native-vlan` statement under the interface's ethernet-switching family, and by default the native VLAN is typically VLAN 1 (though this is configurable).
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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.