The correct answer is that VLANs segment a network into separate broadcast domains, and trunk links like 802.1Q carry traffic for multiple VLANs simultaneously. This is correct because a VLAN creates a logical grouping of devices that share a single broadcast domain, isolating broadcast traffic from other VLANs and reducing unnecessary network congestion. On the JNCIA-Junos exam, this concept tests your understanding of Layer 2 segmentation and how trunk ports use VLAN tags to multiplex traffic from different VLANs over a single physical link, a common scenario in enterprise networks. A frequent trap is confusing VLANs with subnets—remember that VLANs operate at Layer 2 for broadcast isolation, while subnets are Layer 3 logical addressing. For the exam, keep this memory tip: “Trunks tag, VLANs segregate, broadcasts isolate.”
JNCIA-JUNOS Networking Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of networking fundamentals. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Which TWO statements about VLANs are correct? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Trunk links can carry traffic for multiple VLANs.
Option C is correct because trunk links, such as 802.1Q trunk ports, are designed to carry traffic for multiple VLANs by adding VLAN tags to Ethernet frames. This allows a single physical link between switches or between a switch and a router to transport frames from different VLANs simultaneously.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
Common exam trap: answer the scenario, not the keyword
The trap here is that Juniper Networks often tests the misconception that a switch port can belong to only one VLAN, but this is only true for access ports—trunk ports can carry multiple VLANs, and some platforms support voice VLANs that allow a port to be in both a data and voice VLAN simultaneously.
Detailed technical explanation
How to think about this question
Under the hood, VLANs operate at Layer 2 by inserting a 4-byte 802.1Q tag into the Ethernet frame header, which includes a 12-bit VLAN ID (0–4095). Trunk ports use this tag to multiplex multiple VLANs over one link, while access ports strip the tag and associate all untagged frames with a single PVID. In real-world scenarios, trunk links are essential for inter-switch VLAN propagation and for router-on-a-stick configurations where a single router interface routes between VLANs.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Networking Fundamentals — This question tests Networking Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Trunk links can carry traffic for multiple VLANs. — Option C is correct because trunk links, such as 802.1Q trunk ports, are designed to carry traffic for multiple VLANs by adding VLAN tags to Ethernet frames. This allows a single physical link between switches or between a switch and a router to transport frames from different VLANs simultaneously.
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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