We know that VLANs segment network switch into different portions and assign a different subnet to each VLAN. Switches mainly work at layer 2 of the OSI model, such as the Catalyst 2960 Series. The 2960 series switches support over 4,000 VLANs. But, these switches have very limited IPv4 and IPv6 functionality and they do not look at the logical addresses or layer 3 packets.
We also know that VLAN is a broadcast domain, so one broadcast domain cannot communicate with other broadcast domains. Therefore, computers on separate VLANs are unable to communicate without the intervention of a routing device.
In simple words, VLANs logically segment the switch into different subnet or broadcasts and without layer 3 device and some configuration communication between different hosts not possible. So, any device that supports Layer 3 routing, such as a router or a multilayer switch, can be used to do the necessary routing functionality.
The process of forwarding network traffic from one VLAN to another VLAN using routing is known as inter-VLAN routing. The hosts in the VLANs forwards the traffic to the Layer 2 switches, and then the layer 2 switch sends the traffic to layer 3 device then layer 3; devices decides the destination for the traffic according to the to information in the packet. There are three types of inter-VLAN routing we can use to send traffic between different VLANs.
Legacy Inter-VLAN Routing
Router-on-a-Stick Inter-VLAN Routing
Multilayer Switch Inter-VLAN Routing