Which three elements must be used when you configure a router interface for VLAN trunking? (Choose three.)
This scenario is commonly called a router on a stick. A short, well written article on this operation can be found here: http://www.thebryantadvantage.com/RouterOnAStickCCNACertificationExamTutorial.htm
When configuring a router interface for VLAN trunking, the following three elements must be considered:
Subinterface encapsulation identifiers that match VLAN tags: Each subinterface on the router should be configured with an encapsulation type that matches the VLAN tag of the traffic that it will be carrying. This can be either 802.1Q or ISL. The VLAN tag is used to identify traffic belonging to a particular VLAN.
One physical interface for each subinterface: Trunking allows multiple VLANs to be carried over a single physical interface. However, to make this possible, the router must be connected to a switch port that is configured for trunking. Each subinterface must be associated with a physical interface that is connected to a trunk port on a switch.
One subinterface per VLAN: Each subinterface on the router is associated with a specific VLAN. Therefore, a separate subinterface must be created for each VLAN that is being trunked between the switch and the router. The subinterface should be configured with an IP address that corresponds to the IP network or subnetwork of the VLAN.
Therefore, the correct answers to this question are:
Option A is incorrect because a single physical interface can support multiple subinterfaces. Option B is incorrect because a single IP network or subnetwork can be shared by multiple subinterfaces, as long as they belong to different VLANs. Option C is incorrect because a management domain is not a requirement for configuring VLAN trunking on a router interface.