VLANs correspond to unique subnets on the network. For inter-VLAN routing to operate, a router must be connected to all VLANs, either by separate physical interfaces or by subinterfaces. Each interface, or subinterface, must be assigned an IP address that corresponds to the subnet to which it is connected. This permits devices on the VLAN to communicate with the router interface and enables the routing of traffic to other VLANs connected to the router.

The following are some common IP addressing errors: