Inter-VLAN Routing

We create Virtual Local Area Network (VLAN) to isolate the network, meaning that separating the traffic of different departments in an organization. This also divides the one big broadcast domain into multiple small broadcast domains.
In some cases we have to communicate the different VLANs, for instance if we have a printer in sales department and production also wants to use this then we need a communication between these separate VLANs. For this purpose we use inter-VLAN routing, which means routing among VLANs.

This technology can be implemented on switches as well excluding router completely, but for this reason your Switch should be a Layer-3 switch which can support routing feature.
There are two ways to determine whether your switch is layer-3 or not. One is check the license number and other is execute the ip routing command in global configuration if it is accepted by switch it means that switch supports Layer-3 functionality.

This switch does not support Layer-3 functionality.

This switch supports the Layer-3 functionality.

Routing on a Stick (RoaS)

This is an old technique to make communication among different VLANs. This is good technique except one major drawback. This technique use only one link from switch to router and all the traffic is delivered using only one cable which results in performance degradation and in severe cases it results in a bottleneck condition.

ROAS Configuration

This technique is configured in a quite simple manner where we have to make Router aware of VLAN technology by creating sub-interfaces and assigning them number of corresponding VLAN. We also have to create the trunk port on router and connect this to the switch, because the trunk is responsible to transmit the data of multiple VLANs.

Now switch is ready, it has VLANs and configured with trunk mode. Now we need to make router aware of VLANs.

Notice that we created sub-interface for each VLAN and the important thing is that we tell the sub-interface that what VLAN will be responsible for you. The VLAN ID should be same as the VLAN ID in switch because it is important.
The parent interface GigabitEthernet0/0 is put on native-VLAN which is one it takes data and then sends to its child interfaces.

Interface gig0/0.x command creates the sub-interfaces.
Encapsulation dot1q X tells the interface which VLAN is for it and then the IP address, which works as default gateway.

This approach is good except the limitation which we have discussed earlier. There is another better approach in which we can eliminate this task from router and can perform the same on Switch itself and it is very efficient in terms of performance, because switches have a strong back-plan with more bandwidth. This approach is really called Inter-VLAN routing.

Inter-VLAN Routing Configuration

This can be done by creating the Switch Virtual Interface (SVI) on switch, assigning them IP and then turning on the routing functionality by executing ip routing command.

These are the SVI and we can see them in interface list as well.

Now assign VLAN to interfaces and turn on interfaces.

Notice that SVI are now up.

Now the only thing we have to do is to turn on the routing feature or Layer-3 functionality.

Task: Configure Inter-VLAN routing and communicate computers to the router as well.


Prerequisites for 200-301

200-301 is a single exam, consisting of about 120 questions. It covers a wide range of topics, such as routing and switching, security, wireless networking, and even some programming concepts. As with other Cisco certifications, you can take it at any of the Pearson VUE certification centers.

The recommended training program that can be taken at a Cisco academy is called Implementing and Administering Cisco Solutions (CCNA). The successful completion of a training course will get you a training badge.

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