What Is InterVLAN?
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.
A VLAN is a sub-group within a network, which partitions and isolates network traffic at the data link layer (Layer 2) of the OSI model. VLANs are used to segment networks for improved traffic management, enhanced security, and reduced broadcast domains.
In a typical network without intervlan routing, devices within the same VLAN can communicate with each other but not with devices in other VLANs. Intervlan routing overcomes this limitation by enabling devices in different VLANs to communicate. This is typically achieved in one of two ways:
Router-on-a-Stick: This is a common method where a single physical router interface is used to route traffic between multiple VLANs. The router interface is configured as a trunk to allow traffic from all VLANs. VLAN Sub-interfaces are then configured on the router, each representing a VLAN with its own unique IP subnet. This method is cost-effective but can be a bottleneck if a lot of inter-VLAN traffic exists.
Layer 3 Switches: These switches have built-in routing capabilities for handling Layer 3 (network layer) functionalities. They can perform routing tasks along with standard switching operations, thus providing a faster and more efficient solution for intervlan routing compared to the router-on-a-stick approach. Layer 3 switches are preferred in larger networks where high-speed routing is essential.
Diagram showing Intervlan routing.
The figure above shows 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
between VLANs.
■ A router on a stick is configured with a sub-interface for each VLAN and 802.1Q trunk encapsulation.
In conclusion, the choice between these methods depends on factors like network size, traffic volume, performance requirements, and budget constraints.
Understanding and implementing intervlan routing is crucial in modern network design to ensure efficient, secure, and scalable communication across different segments of a network.
Router-On-a-Stick InterVLAN Routing
How to configure Inter-VLAN routing on Cisco Router
Troubleshooting Inter-VLAN Networks
Troubleshooting router-on-a-stick Inter-VLAN Routing Configuration.
