The answer is 802.1Q, the IEEE standard for VLAN tagging on trunk links. This protocol inserts a 4-byte tag into the Ethernet frame header to identify VLAN membership, allowing multiple VLANs to traverse a single trunk link between switches without requiring separate physical links per VLAN. On the CompTIA Network+ N10-009 exam, this concept tests your understanding of how switches segregate broadcast domains while sharing a physical connection; a common trap is confusing 802.1Q with ISL (Cisco’s proprietary protocol) or assuming all untagged frames are dropped. Remember that 802.1Q uses a “native VLAN” concept—frames on the native VLAN remain untagged, while all others carry the tag. A helpful memory tip: think of 802.1Q as the “Q-tip” that inserts a tag into the frame to keep VLANs cleanly separated on the trunk.
N10-009 Network Implementation Practice Question
This N10-009 practice question tests your understanding of network implementation. 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.
A network administrator needs to connect two switches to allow multiple VLANs to traverse the link. Which protocol should be used to tag frames with VLAN information?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
802.1Q
802.1Q is the IEEE standard for VLAN tagging, which inserts a 4-byte tag into the Ethernet frame header to identify the VLAN membership of the frame. This allows multiple VLANs to traverse a single trunk link between switches, enabling inter-switch VLAN communication without requiring separate physical links per VLAN.
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.
✗
STP (Spanning Tree Protocol)
Why it's wrong here
STP prevents loops in redundant switch topologies, but does not tag frames with VLAN information.
✓
802.1Q
Why this is correct
802.1Q is the standard for VLAN tagging on trunk links, ensuring proper VLAN identification across switches.
Related concept
Read the scenario before looking for a memorised answer.
✗
VTP (VLAN Trunking Protocol)
Why it's wrong here
VTP manages VLAN databases across switches but does not tag frames; 802.1Q or ISL are tagging protocols.
✗
LACP (Link Aggregation Control Protocol)
Why it's wrong here
LACP bundles multiple physical links into a single logical link (link aggregation) but does not provide VLAN tagging.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse VTP (a management protocol) with the actual tagging protocol, assuming VTP handles frame tagging because of the word 'trunking' in its name.
Detailed technical explanation
How to think about this question
802.1Q inserts a 4-byte tag between the source MAC address and the EtherType/Length field, consisting of a 2-byte Tag Protocol Identifier (TPID) set to 0x8100 and a 2-byte Tag Control Information (TCI) that includes a 12-bit VLAN ID (0-4095). A subtle behavior is that 802.1Q does not encapsulate the entire frame like ISL; instead, it modifies the original frame, which can cause issues with older hardware that expects a specific frame size. In real-world scenarios, trunk misconfiguration (e.g., native VLAN mismatch) can lead to VLAN hopping or connectivity loss, making proper 802.1Q configuration critical.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 question in full detail.
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 802.1Q — 802.1Q is the IEEE standard for VLAN tagging, which inserts a 4-byte tag into the Ethernet frame header to identify the VLAN membership of the frame. This allows multiple VLANs to traverse a single trunk link between switches, enabling inter-switch VLAN communication without requiring separate physical links per VLAN.
What should I do if I get this N10-009 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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