CCNA Switching and Network Access Practice Question
Network Topology
You are connected to R1. Configure inter-VLAN routing on R1 using router-on-a-stick so that hosts in VLAN 10 (192.168.10.0/24) and VLAN 20 (192.168.20.0/24) can communicate. The switch SW1 is already configured with VLANs and trunking, but R1's current configuration prevents traffic. Identify and fix the issues.
⚠ Common exam trap
A common mistake is overlooking that router-on-a-stick requires the physical interface to be administratively up, as subinterfaces cannot function independently.
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
✓
Enable the physical interface with the 'no shutdown' command on R1.
The issue was that the physical interface GigabitEthernet0/0 on R1 was administratively down, causing all subinterfaces for VLANs 10 and 20 to be in a down state. Enabling it with 'no shutdown' brings the trunk up, allowing inter-VLAN routing because the switch already has trunking configured. The other options are incorrect because they suggest steps that are either already in place (IP routing) or not needed (changing encapsulation or moving no shutdown to subinterfaces).
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Enable the physical interface with the 'no shutdown' command on R1.
Why this is correct
On Cisco routers, subinterfaces do not have an independent administrative state; they inherit their operational status from the parent physical interface. If the physical interface is administratively down (e.g., due to a default shutdown state on some platforms or an explicit shutdown), all subinterfaces remain down regardless of their own configuration. Because the switch trunk is already correctly allowing VLANs 10 and 20, the only missing piece is bringing the physical interface up with the 'no shutdown' command, which restores the subinterfaces to an up/up state and enables routing between VLANs.
- ✗
Change the encapsulation on the subinterfaces to use dot1Q with native VLAN 10 and 20 respectively.
Why it's wrong here
This is incorrect because the native VLAN should be the same on both sides of the trunk; changing it on the router subinterfaces would cause a mismatch. The native VLAN is typically VLAN 1 by default, and subinterfaces for VLANs 10 and 20 should use dot1Q encapsulation without the 'native' keyword.
- ✗
Enable IP routing globally with the 'ip routing' command on R1.
Why it's wrong here
This is incorrect because IP routing is enabled by default on Cisco routers. The issue is not that routing is disabled, but rather that the physical interface is down and the trunk is not allowing the necessary VLANs.
- ✗
Remove the 'no shutdown' from the subinterfaces and apply it only to the physical interface.
Why it's wrong here
This is incorrect because subinterfaces inherit the shutdown state from the physical interface. The physical interface must be enabled with 'no shutdown'; subinterfaces do not have their own shutdown state. Removing 'no shutdown' from subinterfaces is unnecessary and does not fix the issue.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The 200-301 exam frequently reuses these exact scenarios with slightly different constraints.
✓Enable the physical interface with the 'no shutdown' command on R1.Correct answer▾
Why this is correct
On Cisco routers, subinterfaces do not have an independent administrative state; they inherit their operational status from the parent physical interface. If the physical interface is administratively down (e.g., due to a default shutdown state on some platforms or an explicit shutdown), all subinterfaces remain down regardless of their own configuration. Because the switch trunk is already correctly allowing VLANs 10 and 20, the only missing piece is bringing the physical interface up with the 'no shutdown' command, which restores the subinterfaces to an up/up state and enables routing between VLANs.
✗Change the encapsulation on the subinterfaces to use dot1Q with native VLAN 10 and 20 respectively.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: The native VLAN must match between router and switch; using different native VLANs on subinterfaces would break communication.
Why candidates choose this
Candidates might think that each subinterface should match its VLAN's native status, but the native VLAN is a trunk property, not per-VLAN.
✗Enable IP routing globally with the 'ip routing' command on R1.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: 'ip routing' is already enabled by default; disabling it would break routing, but it is not the cause of the problem here.
Why candidates choose this
Candidates often assume that inter-VLAN routing requires explicitly enabling IP routing, but it is on by default.
✗Remove the 'no shutdown' from the subinterfaces and apply it only to the physical interface.Wrong answer — click to see why▾
Why this is wrong here
The specific factual error: Subinterfaces cannot be individually shut; they follow the physical interface state.
Why candidates choose this
Candidates might think subinterfaces can be independently enabled/disabled, but they are logical interfaces that depend on the physical interface.
Analysis generated from the official 200-301blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Visual reference
Go deeper
Related to this question
Learn chapter
Configuring Switch Ports for Desktops, VoIP Phones, APs, IoT, and Virtualized Hosts
Key term
Switch
A switch is a networking device that connects devices on a local area network and uses MAC addresses to forward data only to the intended recipient.
Key term
Inter-VLAN routing
Inter-VLAN routing is the process of forwarding network traffic between different VLANs to enable communication across logically separated broadcast domains.
About these practice questions
Courseiva writes every 200-301 question from scratch — 1,389 in total, each with an explanation and a wrong-answer breakdown. None are copied from real exams or dumps. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 200-301 practice question is part of Courseiva's free Cisco 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 200-301 exam.