We define inter-VLAN routing as a process of forwarding network traffic from one VLAN to another VLAN using a router or layer 3 device.
In the previous pages, we learned about how to configure VLANs on a network switch. To allow devices connected to the various VLANs to communicate with each other, you need to connect a router.
As we’ve learned that each VLAN is a unique broadcast domain, so, computers on separate VLANs are, by default, not able to communicate. There is a way to permit these computers to communicate; it is called inter-VLAN routing.
One of the ways of the ways to carry out inter-VLAN routing is by connecting a router to the switch infrastructure. VLANs are associated with unique IP subnets on the network.
This subnet configuration enables the routing process in a multi-VLAN environment. When using a router to facilitate inter-VLAN routing, the router interfaces can be connected to separate VLANs. Devices on those VLANs communicates with each other via the router.
The figure above show a traditional inter-VLAN routing:
1 Traffic from PC1 on VLAN10 is routed through router R1 to reach PC3 on VLAN 20.
2. PC1 and PC3 are on different VLANs and have IP addresses on different subnets.
3. Router R1 has a separate interface configured for each of the VLANs.
Summary of Routing Between VLANs
■ Inter-VLAN routing using a router on a stick utilizes an external router to pass traffic
■ A router on a stick is configured with a subinterface for each VLAN and 802.1Q trunk