Router-on-a-Stick Configuration

BD

Router-on-a-stick is a technique that allows a router to route traffic between different VLANs that are connected to a single physical interface on the router. To enable router-on-a-stick on a switch, you must perform the following two steps:

1. Configure subinterfaces on the router:

Subinterfaces are virtual interfaces that allow a single physical interface on a router to be divided into multiple logical interfaces. Each subinterface is associated with a specific VLAN, and packets that are received on the physical interface are tagged with the VLAN ID and sent to the appropriate subinterface. To configure subinterfaces on the router, you must use the encapsulation dot1q command followed by the VLAN ID to configure each subinterface. For example, to configure subinterfaces for VLANs 10 and 20 on interface fa0/0, you would use the following commands:

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Router(config)# interface fastethernet 0/0 Router(config-if)# no shutdown Router(config-if)# interface fastethernet 0/0.10 Router(config-subif)# encapsulation dot1q 10 Router(config-subif)# ip address 192.168.10.1 255.255.255.0 Router(config-subif)# interface fastethernet 0/0.20 Router(config-subif)# encapsulation dot1q 20 Router(config-subif)# ip address 192.168.20.1 255.255.255.0 

In this example, subinterface fa0/0.10 is associated with VLAN 10 and has an IP address of 192.168.10.1, while subinterface fa0/0.20 is associated with VLAN 20 and has an IP address of 192.168.20.1.

2. Configure a trunk port on the switch:

To allow traffic from all VLANs to reach the router, you must configure a trunk port on the switch that connects to the router. A trunk port is a switch port that carries traffic for multiple VLANs by tagging the traffic with the VLAN ID. To configure a trunk port on the switch, you must use the switchport mode trunk command on the switch interface that connects to the router. For example, to configure interface gigabitethernet 0/1 as a trunk port, you would use the following commands:

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Switch(config)# interface gigabitethernet 0/1 Switch(config-if)# switchport mode trunk 

In this example, interface gigabitethernet 0/1 is configured as a trunk port, allowing traffic from all VLANs to reach the router.

Therefore, the correct answers are A and D. Answer A is correct because you must configure the subinterface number to match the VLAN ID, and answer D is correct because you must connect the router to a trunk port on the switch. Answer B is incorrect because assigning an access port to a VLAN is not necessary for router-on-a-stick. Answer C is incorrect because you do not need to configure an IP route to the VLAN destination network. Answer E is also incorrect because configuring full duplex is not related to router-on-a-stick configuration.