Inter-VLAN routing is a networking technique that allows communication between different VLANs within a network infrastructure. By default, devices within the same VLAN can communicate with each other, but communication between devices in different VLANs is restricted. Inter-VLAN routing enables communication between devices in different VLANs by routing traffic between them at the Layer 3 (network layer) of the OSI model.

### Purpose of Inter-VLAN Routing:

The primary purpose of inter-VLAN routing is to:

1. **Facilitate Communication**: Enable devices in different VLANs to communicate with each other.
2. **Maintain Network Segmentation**: Preserve the benefits of VLAN segmentation while allowing controlled communication between VLANs.
3. **Implement Security Policies**: Control and monitor traffic flow between VLANs to enforce security policies.

### How Inter-VLAN Routing Works:

Inter-VLAN routing involves the use of a router or a Layer 3 switch to route traffic between VLANs. Here's how it works:

1. **Router or Layer 3 Switch Configuration**: Configure the router or Layer 3 switch to have interfaces in each VLAN that needs to communicate with other VLANs.
   
2. **Subnetting**: Each VLAN is typically associated with a different IP subnet. The router or Layer 3 switch needs to have an IP address in each VLAN subnet to facilitate routing.

3. **Routing Table**: The router or Layer 3 switch maintains a routing table that defines how traffic should be routed between VLANs based on destination IP addresses.

4. **Routing Logic**: When a device in one VLAN sends a packet to a device in another VLAN, the router or Layer 3 switch examines the packet's destination IP address and forwards it to the appropriate VLAN based on the routing table.

5. **Packet Forwarding**: The router or Layer 3 switch forwards the packet between the VLANs, allowing communication between devices in different VLANs.

### Benefits of Inter-VLAN Routing:

- **Improved Communication**: Enables communication between devices in different VLANs, facilitating collaboration and resource sharing.
- **Network Segmentation**: Maintains network segmentation for security and performance reasons while allowing controlled communication between VLANs.
- **Enhanced Security**: Allows for the implementation of security policies and access controls between VLANs to restrict and monitor traffic flow.
- **Scalability**: Supports network growth and expansion by providing a scalable solution for inter-VLAN communication.

### Conclusion:

Inter-VLAN routing is a fundamental networking technique that enables communication between devices in different VLANs within a network infrastructure. By implementing inter-VLAN routing, organizations can maintain network segmentation while facilitating controlled communication and enforcing security policies between VLANs.