Inter-VLAN routing on Layer 3 devices.

Concept of Inter-VLAN Routing? / Define inter-VLAN routing?
Inter-VLAN routing is a process of forwarding network traffic from one VLAN to another VLAN using a router.

VLANs are used to segment switched Layer 2 networks for a variety of reasons. Regardless of the reason, hosts in one VLAN cannot communicate with hosts in another VLAN unless there is a router or a Layer 3 switch to provide routing services.

in short , the process of Inter-VLAN routing is, forwarding network traffic from one VLAN to another VLAN.

There are three inter-VLAN routing options:

Legacy Inter-VLAN routing – This is a legacy solution. It does not scale well.

Router-on-a-Stick – This is an acceptable solution for a small to medium-sized network.

Layer 3 switch using switched virtual interfaces (SVIs) – This is the most scalable solution for medium to large organizations.

Inter-VLAN Routing CCNA
Inter-VLAN Routing CCNA

Briefly explain traditional inter-VLAN routing:

Traditional inter-VLAN routing uses routers with multiple physical interfaces. Each interface is connected to a separate network and configured for a different subnet. The switch ports connect to the router in access mode and a different VLAN is assigned to each port interface. Each router interface can then accept traffic from the VLAN associated with the switch interface that it is connected to, and traffic can be routed to the other VLANs connected to the other interfaces.

Briefly explain “router-on-a-stick” inter-VLAN routing:

“Router-on-a-stick” inter-VLAN routing uses a single physical interface to route traffic between multiple VLANs on a network. The router interface is configured to operate as a trunk link and is connected to a switch port configured in trunk mode. The router performs the inter-VLAN routing by accepting VLAN tagged traffic on the trunk interface coming from the adjacent switch and internally routing between the VLANs using subinterfaces. The router then forwards the routed traffic—VLAN tagged for the destination VLAN—out the same physical interface.

What are subinterfaces?

Subinterfaces are multiple virtual interfaces, associated with one physical interface. These subinterfaces are configured in software.

Inter-VLAN Routing Techniques.

Traditional Inter-VLAN Routing Configuration

 traditional inter-VLAN routing
traditional inter-VLAN routing

In the following lines, record the commands to configure R1 with traditional inter-VLAN routing:
R1(config)#interface fastethernet 0/0
R1(config-if)#ip address 10.10.10.1 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#interface fastethernet 0/1
R1(config-if)#ip address 10.10.30.1 255.255.255.0
R1(config-if)#no shutdown

Router-on-a-Stick Inter-VLAN Routing

Router-on-a-Stick Inter-VLAN Routing
Router-on-a-Stick Inter-VLAN Routing

In the following lines, record the commands to configure R1 with router-on-a-stick inter-VLAN routing:
R1(config)#interface fastethernet 0/0
R1(config-if)#no shutdown
R1(config-if)#interface fastethernet 0/0.10
R1(config-subif)#encapsulation dot1q 10
R1(config-subif)#ip address 10.10.10.1 255.255.255.0
R1(config-subif)#interface fastethernet 0/0.30
R1(config-subif)#encapsulation dot1q 30
R1(config-subif)#ip address 10.10.30.1 255.255.255.0

Layer 3 switch using switched virtual interfaces (SVIs)

Layer 3 switch using switched virtual interfaces (SVIs)
Layer 3 switch using switched virtual interfaces (SVIs)

Complete the following steps to configure S1 with VLANs and trunking:

Step 1. Create the VLANs. In the example, VLANs 10 and 20 are used.

Step 2. Create the SVI VLAN interfaces. The IP address configured will serve as the default gateway for hosts in the respective VLAN.

Step 3. Configure access ports. Assign the appropriate port to the required VLAN.

Step 4. Enable IP routing. Issue the ip routing global configuration command to allow traffic to be exchanged between VLANs 10 and 20. This command must be configured to enable inter-VAN routing on a Layer 3 switch for IPv4.

Use the no switchport command to convert the port to a routed port, then assign an IP address and subnet mask. Enable the port.

Troubleshooting Inter-VLAN Routing

Troubleshooting Inter-VLAN Routing
Troubleshooting Inter-VLAN Routing