350-401 Question 139
Single answerYou are configuring a Layer 3 network for a branch office. The network requires inter-VLAN routing to allow communication between VLAN 10 (192.168.10.0/24) and VLAN 20 (192.168.20.0/24). The branch's router-on-a-stick setup uses a router with a single physical interface (GigabitEthernet0/0) connected to a Layer 2 switch. Which configuration step is necessary to enable inter-VLAN routing?
- A
Assign IP addresses directly to the physical interface of the router and connect it to the switch.
- B
Configure subinterfaces on the router for each VLAN and assign them IP addresses.
- C
Enable Dynamic Trunking Protocol (DTP) on the router interface to negotiate VLAN trunking.
- D
Configure the router interface as an access port for VLAN 10 and VLAN 20.
Show answer and explanation
Correct answer: B
Explanation
In a router-on-a-stick setup, the router uses subinterfaces to route traffic between VLANs. Each subinterface is configured with an IP address that acts as the default gateway for its respective VLAN. The physical interface is configured as a trunk link to carry traffic for multiple VLANs. This setup allows the router to perform inter-VLAN routing efficiently.
- A. Incorrect.
Assigning IP addresses to the physical interface does not enable inter-VLAN routing as it does not support routing for multiple VLANs on a single interface.
- B. Correct.
Configuring subinterfaces on the router and assigning IP addresses to each subinterface is the correct method for enabling inter-VLAN routing in a router-on-a-stick setup.
- C. Incorrect.
Dynamic Trunking Protocol (DTP) is not a valid configuration for a router interface in this scenario. DTP is used for dynamic negotiation of trunk links on switches, not routers.
- D. Incorrect.
Configuring the router interface as an access port is incorrect as access ports are assigned to a single VLAN, which does not support inter-VLAN routing.