Inter-VLAN Routing using Layer 3 Switches
Layer 3 Switch Inter-VLAN Routing
Modern, enterprise networks rarely use router-on-a-stick because it does not scale easily to meet requirements. In these very large networks, network administrators use Layer 3 switches to configure inter-VLAN routing.
Inter-VLAN routing using the router-on-a-stick method is simple to implement for a small to medium-sized organization. However, a large enterprise requires a faster, much more scalable method to provide inter-VLAN routing.
Enterprise campus LANs use Layer 3 switches to provide inter-VLAN routing. Layer 3 switches use hardware-based switching to achieve higher-packet processing rates than routers. Layer 3 switches are also commonly implemented in enterprise distribution layer wiring closets.
Capabilities of a Layer 3 switch include the ability to do the following:
- Route from one VLAN to another using multiple switched virtual interfaces (SVIs).
- Convert a Layer 2 switchport to a Layer 3 interface (i.e., a routed port). A routed port is similar to a physical interface on a Cisco IOS router.
To provide inter-VLAN routing, Layer 3 switches use SVIs. SVIs are configured using the same interface vlan vlan-id command used to create the management SVI on a Layer 2 switch. A Layer 3 SVI must be created for each of the routable VLANs.
Layer 3 Switch Scenario
In the figure, the Layer 3 switch, D1, is connected to two hosts on different VLANs. PC1 is in VLAN 10 and PC2 is in VLAN 20, as shown. The Layer 3 switch will provide inter-VLAN routing services to the two hosts.
The table shows the IP addresses for each VLAN.
D1 VLAN IP Addresses
VLAN Interface | IP Address |
---|---|
10 | 192.168.10.1/24 |
20 | 192.168.20.1/24 |
Layer 3 Switch Configuration
Complete the following steps to configure S1 with VLANs and trunking:
Step 1. Create the VLANs.
Step 2. Create the SVI VLAN interfaces.
Step 3. Configure access ports.
Step 4. Enable IP routing.
Click each button for details of the configuration step.