200-301 Question 5
Single answerA network administrator is configuring a router to allow inter-VLAN communication on a small enterprise network. The router has interfaces for each VLAN and is using subinterfaces for this setup. However, devices in different VLANs are unable to communicate. What is the MOST likely reason for this issue?
- A
The router's interfaces are not assigned the correct IP addresses for each VLAN.
- B
The router does not have a default route configured.
- C
Trunking is not properly configured on the switch port connected to the router.
- D
The VLANs are not assigned to the correct subinterfaces on the router.
Show answer and explanation
Correct answer: C
Explanation
When using a router with subinterfaces for inter-VLAN routing, the switch port connected to the router must be configured as a trunk port. Trunking allows the switch to send VLAN-tagged traffic to the router, which can then process traffic for different VLANs through its subinterfaces. Without proper trunking, the router will not be able to distinguish between VLANs, and inter-VLAN communication will fail.
- A. Incorrect.
While IP addressing is important, incorrect IP addresses on the router's subinterfaces would not completely prevent inter-VLAN communication. Devices might still be able to communicate within their own VLAN.
- B. Incorrect.
A default route is necessary for traffic destined outside the local network, but it is not required for inter-VLAN routing. The issue here is specific to communication between VLANs.
- C. Correct.
If trunking is not configured on the switch port connected to the router, the router will not receive tagged VLAN traffic from the switch, which is essential for inter-VLAN communication using subinterfaces.
- D. Incorrect.
If VLANs are not assigned to the correct subinterfaces, that could cause issues, but it is unlikely to be the primary problem if the router is unable to process VLAN-tagged traffic due to a trunking misconfiguration.