5.3 Inter-VLAN Routing Explained
Key Concepts
Inter-VLAN routing is the process of enabling communication between devices in different VLANs. Key concepts include:
- Router-on-a-Stick: A method where a single physical interface on a router is used to route traffic between multiple VLANs.
- Layer 3 Switch: A switch that performs routing functions at the network layer.
- SVI (Switch Virtual Interface): A virtual interface on a Layer 3 switch that represents a VLAN.
- Trunking: The process of carrying multiple VLANs over a single link.
- Routing Protocols: Methods used by routers to exchange routing information.
Router-on-a-Stick
Router-on-a-Stick is a cost-effective method for inter-VLAN routing. It involves configuring subinterfaces on a single physical interface of a router. Each subinterface is associated with a specific VLAN and is assigned an IP address from the VLAN's subnet.
Example: Suppose you have a router with one Ethernet interface (eth0) and three VLANs (VLAN 10, VLAN 20, and VLAN 30). You would create subinterfaces eth0.10, eth0.20, and eth0.30, each with an IP address from the respective VLAN's subnet.
Layer 3 Switch
A Layer 3 switch combines the functions of a switch and a router. It can route traffic between different VLANs within the same switch. Layer 3 switches are more efficient than traditional routers for inter-VLAN routing because they operate at higher speeds and have lower latency.
Example: In a large enterprise network, a Layer 3 switch might be used to route traffic between VLANs within the same building. This setup reduces the need for multiple physical routers and simplifies network management.
SVI (Switch Virtual Interface)
An SVI is a virtual interface on a Layer 3 switch that represents a VLAN. Each SVI is assigned an IP address from the VLAN's subnet and is used for routing traffic between VLANs. SVIs allow for centralized management of VLANs and simplify network configuration.
Example: On a MikroTik switch, you might create an SVI for VLAN 10 with the IP address 192.168.10.1/24. This SVI would handle all routing for devices in VLAN 10, allowing them to communicate with devices in other VLANs.
Trunking
Trunking is the process of carrying multiple VLANs over a single link. Trunk ports on switches and routers are configured to carry traffic for multiple VLANs, allowing for efficient use of network resources. Trunking is essential for inter-VLAN routing because it enables the transmission of VLAN-tagged traffic between devices.
Example: In a network with multiple switches, trunking would be configured on the links between the switches. This allows all VLANs to be transmitted over a single link, reducing the number of physical connections required.
Routing Protocols
Routing protocols are methods used by routers to exchange routing information. Common routing protocols include OSPF, EIGRP, and BGP. These protocols allow routers to dynamically learn about the network and make routing decisions based on the best path to reach a destination.
Example: In a large campus network, OSPF might be used to dynamically route traffic between different buildings. Routers in each building would exchange routing information, allowing them to determine the best path for inter-VLAN traffic.