When separate VLANs are created, by default, they cannot communicate directly with each other. However, in many situations, it is necessary to allow communication between different VLANs to share resources or allow users to access specific services on other virtual networks. This is where the routing between VLANs.

Inter-VLAN routing allows traffic to move between different VLANs by using a routing device or layer 3 switch that has routing capability. These devices act as bridges between VLANs and allow them to communicate with each other.

Ways to implement routing

The main ways to implement routing between VLANs are:

1. Routing with an external router

In this configuration, each VLAN is connected to its own interface on the router. When a data packet needs to be sent from one VLAN to another, it is sent to the router, which then forwards it to the destination VLAN. This technique is simple and effective, but can be inefficient if there are many VLANs, since it requires a separate interface for each.

2. Routing at Layer 3 Switching

In this configuration, routing is performed within the switch, which can understand and manipulate packets at the network level. This type of switch has multiple virtual Layer 3 interfaces, one for each VLAN, allowing you to route between them. This technique is more efficient than routing with an external router, but requires more sophisticated and expensive hardware.

3. Routing with a trunk (Router-on-a-stick)

In this configuration, a single physical interface on a router is used to handle traffic from multiple VLANs. VLANs are differentiated using VLAN (802.1Q) tags on data packets. This technique is more efficient than routing with an external router in terms of interface usage, but may be limited by the amount of bandwidth available on the trunk interface.

Essential steps

When configuring routing between VLANs, several steps must be performed:

1. VLAN configuration

First, individual VLANs are created on the switches or network devices. Each VLAN is configured with a unique ID and specific ports are assigned to each VLAN.

2. Configuration of routing interfaces

On the routing device or Layer 3 switch, the interfaces that will connect to each VLAN must be configured. These interfaces are configured with IP addresses belonging to the subnets of each VLAN.

3. Routing table configuration

Static routes are configured or a dynamic routing protocol is used to allow the routing device to know how to reach the subnets of each VLAN.

4. Establishment of access policies

Access control lists (ACLs) can be applied to control what traffic is allowed or blocked between VLANs. This provides an additional layer of security and control.

Once these steps are completed, the VLANs will be interconnected and will be able to communicate with each other through the routing device or layer 3 switch. The routing device will examine the destination information of the packets and route them to the corresponding destination VLAN.

It is important to note that routing between VLANs can have an impact on network performance as it involves additional packet processing and can generate additional traffic on the network.

Therefore, it is important to carefully design the routing configuration and consider the available bandwidth and resources to ensure optimal network performance.

Layer 3 Routers or Switches

The choice between using a router or a Layer 3 switch for routing between VLANs will depend on several factors, including the size of the network, the volume of traffic, available resources, and the specific needs of the organization.

Here are some considerations that can help you make a decision:

1 performance

Layer 3 switches are typically faster than routers for routing, since the switch hardware is designed to handle high-speed packet routing. This can be especially important on networks with a large amount of inter-VLAN traffic.

2. Cost

Layer 3 switches are typically more expensive than routers due to their specialized hardware. Therefore, if budget is an important consideration, a router may be a more cost-effective option.

3. Scalability

If the network is intended to grow in size and complexity, a Layer 3 switch may be a more scalable option. Layer 3 switches can handle large numbers of VLANs and provide inter-VLAN routing without the need for additional physical interfaces as required by a router.

4. Advanced features

Routers typically offer a wider range of advanced features compared to Layer 3 switches. These may include support for a wider range of routing protocols, firewall capabilities, VPNs, and other security features.

5. Ease of configuration and management

Layer 3 switches are typically easier to configure and manage for inter-VLAN routing compared to routers. This is because you can configure multiple VLAN interfaces on a single device instead of having to manage multiple physical interfaces on a router.

In summary, choosing between a router and a Layer 3 switch for inter-VLAN routing will depend on the specific needs of your network. Both options have advantages and disadvantages, and the best option will vary from situation to situation.

Routers versus Layer 3 Switches

Below, we present a comparative table that highlights some of the advantages offered by both routers as layer 3 switches for routing between VLANs in a network: