Using a VLANIF Interface to Implement Layer 3 Connectivity Between the Switch and Router

To reduce costs, most enterprises use switches to connect internal devices and an egress router to connect to an ISP network, as shown in Figure 1.

Figure 1 Connection between the switch and router

To access the ISP network, the core Layer 3 switch and egress router need to interwork at Layer 3. Most Layer 3 switches do not support or only support limited routed interfaces. Generally, a VLANIF interface is used as a Layer 3 interface to communicate with the Layer 3 sub-interface of the router. Then a static route or a dynamic routing protocol is configured to implement Layer 3 connectivity between the core switch and egress router.