This 200-301 practice question tests your understanding of connected to r1. 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.
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 ! R1#show running-config | include ip routing no ip routing R1#show interfaces trunk Port Mode Encapsulation Status Native vlan Gi0/0 on 802.1q trunking 99 Port Vlans allowed on trunk Gi0/0 10,20 Port Vlans allowed and active in management domain Gi0/0 10
You are connected to R1. The network consists of R1, SW1, and two hosts (Host-A on VLAN 10, Host-B on VLAN 20). SW1 has two access ports (one per VLAN) and a trunk to R1. Configure R1 for router-on-a-stick inter-VLAN routing. The current configuration has a native VLAN mismatch and a missing subinterface for VLAN 20. Fix these issues so that Host-A and Host-B can ping each other.
Correct answer & explanation
The native VLAN mismatch exists: R1 expects native VLAN 99, but SW1 likely uses native VLAN 1 (default). This causes CDP/STP issues but not directly inter-VLAN routing; however, for proper operation, set native VLAN to 1 on R1. Additionally, the subinterface for VLAN 20 is missing, so traffic from VLAN 20 cannot be routed. Finally, 'ip routing' is disabled, preventing any inter-VLAN routing. Solution: change native VLAN on trunk to 1, create subinterface G0/0.20 with encapsulation dot1Q 20 and IP 192.168.20.1/24, and enable 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.
Common exam traps
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
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.
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
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
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.
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Practice this exam
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FAQ
Access ports place end devices into a single VLAN.
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.
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.
Access ports place end devices into a single VLAN.
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