This LFCS practice question tests your understanding of networking. 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 nmcli command creates a VLAN interface with tag 10 on device eth0?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
nmcli connection add type vlan con-name vlan10 dev eth0 id 10
Option B is correct because the `nmcli connection add` command with `type vlan` requires the `dev` option to specify the parent interface (eth0) and the `id` option to set the VLAN tag (10). The `con-name` assigns a name to the connection profile, and the resulting interface will be named automatically (e.g., eth0.10) unless overridden by `ifname`. This creates a VLAN interface that tags frames with ID 10 on the parent device eth0.
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.
✗
nmcli connection add type vlan con-name vlan10 ifname eth0 id 10
Why it's wrong here
The correct parameter is 'dev', not 'ifname'.
✓
nmcli connection add type vlan con-name vlan10 dev eth0 id 10
Why this is correct
This is the correct syntax to create a VLAN connection on eth0 with ID 10.
Related concept
Read the scenario before looking for a memorised answer.
✗
nmcli device add vlan con-name vlan10 dev eth0 id 10
Why it's wrong here
'nmcli device add' is not a valid command.
✗
nmcli connection add type vlan con-name vlan10 ifname eth0.10
Why it's wrong here
This would create a connection with a specific ifname but not necessarily a VLAN.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing `ifname` (which sets the resulting interface name) with `dev` (which specifies the parent device), leading candidates to incorrectly use `ifname eth0` instead of `dev eth0` when the intent is to attach the VLAN to the physical interface.
Trap categories for this question
Command / output trap
'nmcli device add' is not a valid command.
Detailed technical explanation
How to think about this question
VLAN interfaces in Linux use 802.1Q encapsulation, where each frame is tagged with a VLAN ID (0-4095) in the Ethernet header. The `nmcli` command creates a NetworkManager connection profile that persists across reboots; the `dev` option binds the VLAN to a specific parent interface, and the `id` sets the 802.1Q tag. Without the `id` option, the VLAN interface will not function correctly because the kernel's VLAN module (8021q) requires the tag to be explicitly defined for proper packet classification.
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 — This question tests Networking — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: nmcli connection add type vlan con-name vlan10 dev eth0 id 10 — Option B is correct because the `nmcli connection add` command with `type vlan` requires the `dev` option to specify the parent interface (eth0) and the `id` option to set the VLAN tag (10). The `con-name` assigns a name to the connection profile, and the resulting interface will be named automatically (e.g., eth0.10) unless overridden by `ifname`. This creates a VLAN interface that tags frames with ID 10 on the parent device eth0.
What should I do if I get this LFCS 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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