Three ways to route between VLANs: a separate router interface per VLAN (legacy), a single router-on-a-stick using subinterfaces, and an L3 switch with SVIs (Switched Virtual Interfaces). This chapter walks through the two modern patterns end to end.
Connect a single router interface to a switch trunk port. Create one subinterface on the router per VLAN, each with its own IP and 'encapsulation dot1Q <vlan>' command. Each PC's default gateway is the router subinterface IP for its VLAN.
R1(config)# interface Gi0/0
R1(config-if)# no shutdown
R1(config)# interface Gi0/0.10
R1(config-subif)# encapsulation dot1Q 10
R1(config-subif)# ip address 10.0.10.1 255.255.255.0
R1(config)# interface Gi0/0.20
R1(config-subif)# encapsulation dot1Q 20
R1(config-subif)# ip address 10.0.20.1 255.255.255.0An SVI (interface VlanX) is a virtual L3 interface inside a switch that represents the entire VLAN as a single routable interface. With ip routing enabled the switch forwards inter-VLAN traffic in hardware — far faster than a single router-on-a-stick link.
Switch(config)# ip routing
Switch(config)# interface Vlan10
Switch(config-if)# ip address 10.0.10.1 255.255.255.0
Switch(config-if)# no shutdown
Switch(config)# interface Vlan20
Switch(config-if)# ip address 10.0.20.1 255.255.255.0
Switch(config-if)# no shutdown1 more section in this chapter, plus a 2-question quiz and a hands-on lab.
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