The answer is to configure R1’s physical interface GigabitEthernet0/0 with `no shutdown`, `switchport trunk native vlan 99`, and `switchport trunk allowed vlan 10,20`, then enable `ip routing` globally. This corrects the native VLAN mismatch because the router’s subinterface for native VLAN 99 expects the switch trunk to also use VLAN 99 as the native VLAN, but the switch defaults to VLAN 1—causing a mismatch that drops control traffic and can block VLAN 20 communication. Additionally, the trunk must explicitly permit VLAN 20, and `ip routing` is required on the router to forward packets between VLAN 10 and 20 subinterfaces. On the CCNA 200-301 v2 exam, this scenario tests your understanding of router-on-a-stick configuration and troubleshooting, specifically how native VLAN mismatches and missing `ip routing` break inter-VLAN routing. A common trap is forgetting that subinterface encapsulation must match the VLAN ID, or assuming the physical interface is already up. Memory tip: “Native must match, trunk must allow, and routing must be on.”
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.
Exhibit
R1#show running-config
Building configuration...
Current configuration : 1024 bytes
!
hostname R1
!
interface GigabitEthernet0/0
no shutdown
!
interface GigabitEthernet0/0.10
encapsulation dot1Q 10
ip address 10.0.10.1 255.255.255.0
!
interface GigabitEthernet0/0.20
encapsulation dot1Q 20
ip address 10.0.20.1 255.255.255.0
!
interface GigabitEthernet0/0.99
encapsulation dot1Q 99 native
ip address 192.168.99.1 255.255.255.0
!
end
R1#show interfaces trunk
Port Mode Encapsulation Status Native vlan
Gig0/0.10 on 802.1q trunking 1
Gig0/0.20 on 802.1q trunking 1
Gig0/0.99 on 802.1q trunking 99
Port Vlans allowed on trunk
Gig0/0.10 1-1005
Gig0/0.20 1-1005
Gig0/0.99 1-1005
R1#show ip route
Codes: C - connected, S - static, I - IGP, R - RIP, ...
Gateway of last resort is not set
10.0.0.0/24 is subnetted, 2 subnets
C 10.0.10.0/24 is directly connected, GigabitEthernet0/0.10
C 10.0.20.0/24 is directly connected, GigabitEthernet0/0.20
192.168.99.0/24 is subnetted, 1 subnets
C 192.168.99.0/24 is directly connected, GigabitEthernet0/0.99
R1#show vlan brief
<no output — switch not R1>
You are connected to R1. The network uses a router-on-a-stick design with a single switch (SW1) and two VLANs: VLAN 10 (10.0.10.0/24) and VLAN 20 (10.0.20.0/24). The current configuration has connectivity issues: PCs in VLAN 20 cannot ping the router interface or each other, and there is a native VLAN mismatch on the trunk. Configure R1 to correct the native VLAN mismatch, ensure the trunk allows both VLANs, enable inter-VLAN routing, and fix any subinterface encapsulation errors so that all PCs can reach the router and each other across VLANs.
R1#show running-config
Building configuration...
Current configuration : 1024 bytes
!
hostname R1
!
interface GigabitEthernet0/0
no shutdown
!
interface GigabitEthernet0/0.10
encapsulation dot1Q 10
ip address 10.0.10.1 255.255.255.0
!
interface GigabitEthernet0/0.20
encapsulation dot1Q 20
ip address 10.0.20.1 255.255.255.0
!
interface GigabitEthernet0/0.99
encapsulation dot1Q 99 native
ip address 192.168.99.1 255.255.255.0
!
end
R1#show interfaces trunk
Port Mode Encapsulation Status Native vlan
Gig0/0.10 on 802.1q trunking 1
Gig0/0.20 on 802.1q trunking 1
Gig0/0.99 on 802.1q trunking 99
Port Vlans allowed on trunk
Gig0/0.10 1-1005
Gig0/0.20 1-1005
Gig0/0.99 1-1005
R1#show ip route
Codes: C - connected, S - static, I - IGP, R - RIP, ...
Gateway of last resort is not set
10.0.0.0/24 is subnetted, 2 subnets
C 10.0.10.0/24 is directly connected, GigabitEthernet0/0.10
C 10.0.20.0/24 is directly connected, GigabitEthernet0/0.20
192.168.99.0/24 is subnetted, 1 subnets
C 192.168.99.0/24 is directly connected, GigabitEthernet0/0.99
R1#show vlan brief
<no output — switch not R1>
A
interface gig0/0
no shutdown
switchport trunk native vlan 99
switchport trunk allowed vlan 10,20
ip routing
This sequence correctly addresses the native VLAN mismatch by setting the native VLAN to 99 on the physical interface, ensures the trunk allows both VLANs, and enables IP routing for inter-VLAN communication.
B
interface gig0/0.10
encapsulation dot1Q 10
ip address 10.0.10.1 255.255.255.0
interface gig0/0.20
encapsulation dot1Q 20
ip address 10.0.20.1 255.255.255.0
Why wrong: This only configures subinterfaces but does not address the native VLAN mismatch on the physical interface, nor does it enable IP routing.
C
interface gig0/0
no shutdown
switchport trunk native vlan 1
switchport trunk allowed vlan 10,20
ip routing
Why wrong: Setting native VLAN to 1 does not match the switch's expectation of native VLAN 99, so the mismatch persists.
D
interface gig0/0
no shutdown
switchport trunk native vlan 99
switchport trunk allowed vlan 10,20
no ip routing
Why wrong: Disabling IP routing prevents the router from forwarding traffic between VLANs, breaking inter-VLAN routing.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
interface gig0/0
no shutdown
switchport trunk native vlan 99
switchport trunk allowed vlan 10,20
ip routing
The issue is a native VLAN mismatch: R1 subinterface .99 uses native VLAN 99, but the switch expects native VLAN 1 (default). Additionally, VLAN 20 traffic may be blocked if the switch trunk does not allow VLAN 20, and 'ip routing' is missing on R1 (though it appears to have routes, but the command may not be present). The fix: on R1, set the native VLAN on the physical interface to 99 (or match switch), ensure the trunk allows VLANs 10 and 20, and enable IP routing. Also verify subinterface encapsulation is correct. In this case, the candidate must issue 'interface gig0/0', 'no shutdown', 'switchport trunk native vlan 99', 'switchport trunk allowed vlan 10,20', and 'ip routing'.
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.
✓
interface gig0/0
no shutdown
switchport trunk native vlan 99
switchport trunk allowed vlan 10,20
ip routing
Why this is correct
This sequence correctly addresses the native VLAN mismatch by setting the native VLAN to 99 on the physical interface, ensures the trunk allows both VLANs, and enables IP routing for inter-VLAN communication.
Related concept
Access ports place end devices into a single VLAN.
✗
interface gig0/0.10
encapsulation dot1Q 10
ip address 10.0.10.1 255.255.255.0
interface gig0/0.20
encapsulation dot1Q 20
ip address 10.0.20.1 255.255.255.0
Why it's wrong here
This only configures subinterfaces but does not address the native VLAN mismatch on the physical interface, nor does it enable IP routing.
✗
interface gig0/0
no shutdown
switchport trunk native vlan 1
switchport trunk allowed vlan 10,20
ip routing
Why it's wrong here
Setting native VLAN to 1 does not match the switch's expectation of native VLAN 99, so the mismatch persists.
✗
interface gig0/0
no shutdown
switchport trunk native vlan 99
switchport trunk allowed vlan 10,20
no ip routing
Why it's wrong here
Disabling IP routing prevents the router from forwarding traffic between VLANs, breaking inter-VLAN routing.
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.
✓interface gig0/0
no shutdown
switchport trunk native vlan 99
switchport trunk allowed vlan 10,20
ip routingCorrect answer▾
Why this is correct
This sequence correctly addresses the native VLAN mismatch by setting the native VLAN to 99 on the physical interface, ensures the trunk allows both VLANs, and enables IP routing for inter-VLAN communication.
✗interface gig0/0.10
encapsulation dot1Q 10
ip address 10.0.10.1 255.255.255.0
interface gig0/0.20
encapsulation dot1Q 20
ip address 10.0.20.1 255.255.255.0Wrong answer — click to see why▾
Why this is wrong here
Missing commands to set native VLAN on the physical interface and enable ip routing.
Why candidates choose this
Candidates often think subinterface configuration alone is sufficient for router-on-a-stick, ignoring the native VLAN and routing requirements.
✗interface gig0/0
no shutdown
switchport trunk native vlan 1
switchport trunk allowed vlan 10,20
ip routingWrong answer — click to see why▾
Why this is wrong here
The native VLAN should match the switch's native VLAN (99), not default to 1.
Why candidates choose this
Candidates may assume native VLAN should always be 1 (default) and forget to match the switch configuration.
✗interface gig0/0
no shutdown
switchport trunk native vlan 99
switchport trunk allowed vlan 10,20
no ip routingWrong answer — click to see why▾
Why this is wrong here
IP routing must be enabled for the router to route between subinterfaces.
Why candidates choose this
Candidates might confuse 'ip routing' with 'ip route' or think routing is automatic on routers.
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.
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: interface gig0/0
no shutdown
switchport trunk native vlan 99
switchport trunk allowed vlan 10,20
ip routing — The issue is a native VLAN mismatch: R1 subinterface .99 uses native VLAN 99, but the switch expects native VLAN 1 (default). Additionally, VLAN 20 traffic may be blocked if the switch trunk does not allow VLAN 20, and 'ip routing' is missing on R1 (though it appears to have routes, but the command may not be present). The fix: on R1, set the native VLAN on the physical interface to 99 (or match switch), ensure the trunk allows VLANs 10 and 20, and enable IP routing. Also verify subinterface encapsulation is correct. In this case, the candidate must issue 'interface gig0/0', 'no shutdown', 'switchport trunk native vlan 99', 'switchport trunk allowed vlan 10,20', and 'ip routing'.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. You are connected to SW1 via the console. SW1 is a Layer 2 switch with two VLANs: VLAN 10 (Sales) and VLAN 20 (Engineering). Port G0/1 is connected to a sales PC, and port G0/2 is connected to an engineering PC. You need to ensure that each PC is in the correct VLAN. However, the sales PC is currently unable to ping the engineering PC because they are in different VLANs. You have a router R1 connected to SW1 via port G0/3. Configure inter-VLAN routing using Router-on-a-Stick on R1, and ensure SW1's port G0/3 is properly configured as a trunk.
medium
✓ A.Configure subinterfaces on R1 with encapsulation dot1Q and assign IP addresses in VLAN 10 and VLAN 20. Configure SW1 interface G0/3 as a trunk port.
B.Configure a routed port on SW1 G0/3 and assign an IP address. Then configure static routes on R1 to reach each VLAN.
C.Configure SW1 interface G0/3 as an access port in VLAN 10. Then configure R1 with a single IP address in VLAN 10 and enable proxy ARP.
D.Configure SW1 interface G0/3 as a trunk port. Then configure R1 with a single IP address on the physical interface and enable VLAN routing using the 'vlan' command.
Why A: Router-on-a-Stick allows a single router interface to route between VLANs by using subinterfaces with 802.1Q encapsulation. The switch port must be a trunk to carry the tagged frames. This configuration enables communication between VLAN 10 and VLAN 20.
Variation 2. You are connected to R1. The network has three departments: Sales (VLAN 10, 192.168.1.0/24), Engineering (VLAN 20, 192.168.2.0/24), and Management (VLAN 99, 192.168.99.0/24). A single switch SW1 connects to R1 via trunk interface G0/0. Subinterfaces for VLANs 10, 20, and 99 are already configured on R1 with correct encapsulation and IP addresses. However, inter-VLAN communication is failing. Troubleshoot and fix the configuration issue on R1 to enable routing between all VLANs.
hard
✓ A.Enable 'ip routing' globally on R1.
B.Configure a subinterface for VLAN 1 and assign it an IP address.
C.Change the encapsulation on the subinterfaces from dot1Q to ISL.
D.Add a static route on R1 pointing to each VLAN subnet.
Why A: The router has correctly configured subinterfaces with 802.1Q encapsulation and IP addresses for VLANs 10, 20, and 99. However, 'ip routing' is disabled globally, so the router cannot forward packets between subinterfaces. Additionally, the native VLAN on the trunk is VLAN 1, but no subinterface for VLAN 1 is configured, and the native VLAN mismatch could cause issues; however, the main problem is the lack of IP routing. Enable 'ip routing' globally and optionally configure a subinterface for the native VLAN if needed. The solution requires only 'ip routing' to enable inter-VLAN routing.
Variation 3. You are connected to R1. The network uses a router-on-a-stick design with a single switch (SW1) and two VLANs (10 and 20). Currently, hosts in VLAN 10 cannot ping hosts in VLAN 20, and the trunk between R1 and SW1 shows a native VLAN mismatch. Examine the provided configuration and output, then apply the necessary corrections to R1 so that inter-VLAN routing works correctly.
hard
✓ A.Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.20 to dot1Q 20, and enable IP routing globally.
B.Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.20 to dot1Q 20, but do not enable IP routing because it is enabled by default.
C.Change the native VLAN on R1's trunk interface to 1, correct the encapsulation on G0/0.20 to dot1Q 20, and enable IP routing globally.
D.Change the native VLAN on R1's trunk interface to 99, correct the encapsulation on G0/0.10 to dot1Q 10, and enable IP routing globally.
Why A: The configuration has three issues: 1) The native VLAN on the trunk is VLAN 1, but the switch expects VLAN 99 (common mismatch scenario). 2) Subinterface G0/0.20 uses encapsulation dot1Q 10 instead of 20, causing VLAN 20 traffic to be mis-tagged. 3) The 'ip routing' command is missing globally, so R1 cannot route between subinterfaces. To fix, configure the main interface G0/0 with 'encapsulation dot1Q 99 native' to set the native VLAN to 99, correct the encapsulation on G0/0.20 to 'dot1Q 20', and enable IP routing with 'ip routing'.
Last reviewed: Jun 6, 2026
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