CCNA Switching and Network Access Practice Question
This 200-301 practice question tests your understanding of switching and network access. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
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.
R1#show running-config | section interface GigabitEthernet0/0
interface GigabitEthernet0/0
no ip address
duplex auto
speed auto
!
interface GigabitEthernet0/0.10
encapsulation dot1Q 10
ip address 192.168.10.1 255.255.255.0
!
interface GigabitEthernet0/0.20
encapsulation dot1Q 20
ip address 192.168.20.1 255.255.255.0
!
R1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.10.0/24 is directly connected, GigabitEthernet0/0.10
L 192.168.10.1/32 is directly connected, GigabitEthernet0/0.10
192.168.20.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.20.0/24 is directly connected, GigabitEthernet0/0.20
L 192.168.20.1/32 is directly connected, GigabitEthernet0/0.20
R1#show interfaces trunk
Port Mode Encapsulation Status Native vlan
Gig0/0 on 802.1q trunking 1
Port Vlans allowed on trunk
Gig0/0 1-1005
Port Vlans allowed and active in management domain
Gig0/0 1
Port Vlans in spanning tree forwarding state and not pruned
Gig0/0 1
A
Enable the physical interface with the 'no shutdown' command on R1.
The physical interface must be up for all subinterfaces to function; enabling it resolves the issue because the switch trunk is already properly configured.
B
Change the encapsulation on the subinterfaces to use dot1Q with native VLAN 10 and 20 respectively.
Why wrong: 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.
C
Enable IP routing globally with the 'ip routing' command on R1.
Why wrong: 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.
D
Remove the 'no shutdown' from the subinterfaces and apply it only to the physical interface.
Why wrong: 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.
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).
Key principle: A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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
The physical interface must be up for all subinterfaces to function; enabling it resolves the issue because the switch trunk is already properly configured.
Related concept
Access ports place end devices into a single VLAN.
✗
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
The physical interface must be up for all subinterfaces to function; enabling it resolves the issue because the switch trunk is already properly configured.
✗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?”
Common exam traps
Common exam trap: an active trunk can still block the VLAN you need
A trunk being up does not prove every VLAN is crossing it. Check allowed VLAN lists, native VLAN mismatch, VLAN existence and access-port assignment.
Trap categories for this question
Keyword trap
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.
Detailed technical explanation
How to think about this question
VLAN questions usually combine access-port and trunking clues. The key is to identify whether the issue is local to one switchport, caused by the trunk, or caused by the VLAN not existing where it needs to exist.
KKey Concepts to Remember
Access ports place end devices into a single VLAN.
Trunk ports carry multiple VLANs between switches.
Allowed VLAN lists decide which VLANs can cross a trunk.
Native VLAN mismatch can create confusing symptoms.
TExam Day Tips
→Use show vlan brief to verify access VLANs.
→Use show interfaces trunk to verify trunk state and allowed VLANs.
→Do not treat every same-VLAN issue as a routing problem.
Key takeaway
A trunk being up does not mean the VLAN is allowed across it. Always verify the allowed VLAN list and whether the VLAN exists on both switches.
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 200-301 question in full detail.
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
Switching and Network Access — This question tests Switching and Network Access — Access ports place end devices into a single VLAN..
What is the correct answer to this question?
The correct answer is: 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).
What should I do if I get this 200-301 question wrong?
Review VLAN allowed lists, native VLAN mismatch detection, and how to verify VLAN membership with show vlan brief and show interfaces trunk. Then practise related 200-301 questions on switching, trunking, and access-port configuration.
What is the key concept behind this question?
Access ports place end devices into a single VLAN.
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