Introduction

VLAN (Virtual Local Area Network) is an essential part of modern network design and management. In the context of FortiGate firewalls, VLANs help manage traffic, improve network performance, and enhance security by segregating network traffic. Configuring VLANs correctly ensures smooth communication between various devices and prevents unauthorized access to sensitive network segments.

This complete guide will walk you through everything you need to know about VLAN configuration on a FortiGate Firewall, from the basics to advanced configurations. You will learn how to configure VLANs both through the FortiGate Web Interface and CLI (Command Line Interface), making it a perfect resource for network engineers and IT professionals.

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A VLAN (Virtual Local Area Network) is a logical subnetwork that groups together a collection of devices from different physical LANs. The primary purpose of a VLAN is to separate network traffic, improve performance, and enhance security by isolating certain network segments.

Each VLAN is identified by a unique VLAN ID, and traffic between different VLANs is usually controlled by Layer 3 routing. FortiGate firewalls support VLAN configurations that allow network administrators to define network boundaries for different departments or functions within an organization.

Why VLANs are Important on FortiGate Firewalls

FortiGate firewalls offer powerful network security capabilities, and VLANs play an important role in defining and enforcing network security policies. Here’s why VLANs are important when working with FortiGate:

1. Traffic Segmentation: VLANs enable network traffic segmentation, reducing broadcast traffic and improving overall network performance.
2. Enhanced Security: By segregating traffic into different VLANs, sensitive data can be isolated from the rest of the network, minimizing the chances of unauthorized access.
3. Simplified Management: VLANs make managing large networks more efficient by allowing you to group devices logically, regardless of their physical location.
4. Improved Network Performance: By reducing unnecessary traffic in a VLAN, you can improve the bandwidth efficiency and reduce network congestion.

Step-by-Step Guide to Configuring VLANs on a FortiGate Firewall

Step 1: Access the FortiGate Web Interface

Before you can configure VLANs on your FortiGate firewall, you need to access the FortiGate Web Interface. Follow these steps:

1. Open a web browser and navigate to the FortiGate firewall’s IP address (default is 192.168.1.99).
2. Log in using your administrator credentials.

Once logged in, you’ll be directed to the dashboard, where you can manage the firewall’s settings, including VLAN configurations.

Step 2: Creating VLAN Interfaces

To create a VLAN interface on the FortiGate firewall:

1. Go to Network > Interfaces.
2. Click Create New > Interface.
3. Select Type: VLAN.
4. Enter a VLAN ID (for example, VLAN 10).
5. Set the Parent Interface (this is the physical interface that will carry the VLAN traffic).
6. Set the IP Address and Subnet Mask for the VLAN interface.
7. Click OK to save the configuration.

Step 3: Assigning VLANs to Physical Interfaces

Once the VLAN interface is created, you need to assign it to a physical interface. This allows the physical network to recognize and transmit VLAN traffic.

1. Go to Network > Interfaces.
2. Locate the VLAN interface created earlier.
3. Under the Interface column, select the physical interface you want to assign it to.
4. Save the configuration.

Step 4: Configuring DHCP for VLANs

You can enable DHCP on VLAN interfaces to automatically assign IP addresses to devices in that VLAN.

1. Navigate to Network > DHCP Server.
2. Select the VLAN interface.
3. Enable DHCP and set the IP range and gateway address.
4. Save the configuration.

Step 5: Setting Up Firewall Policies for VLANs

To allow traffic between VLANs or control inbound and outbound traffic, you need to create firewall policies.

1. Go to Policy & Objects > IPv4 Policy.
2. Create a new policy by clicking Create New.
3. Set the Source Interface as the VLAN interface and the Destination Interface as the interface you want to communicate with.
4. Set the Action to Accept and configure any service rules (e.g., HTTP, HTTPS, etc.).
5. Save the policy.

Step 6: Configuring Inter-VLAN Routing

For devices in different VLANs to communicate with each other, you need to configure Inter-VLAN routing. You can enable static routes or configure FortiGate’s built-in routing.

1. Go to Router > Static Routes.
2. Create a new static route for the VLAN subnet, defining the gateway.
3. Save the configuration.

Step 7: Implementing VLAN Security Best Practices

VLANs can be used to enhance the security of your network, but certain best practices must be followed:

1. Disable unused VLAN interfaces to minimize potential attack surfaces.
2. Implement Access Control Lists (ACLs) to control which devices can access which VLANs.
3. Use 802.1X Authentication to ensure only authorized devices can connect to the network.

Step 8: Troubleshooting VLAN Configuration Issues

If you encounter issues with your VLAN configuration, use the following troubleshooting techniques:

• Check the VLAN interface status and ensure it’s up.
• Verify the IP addressing scheme to ensure no conflicts.
• Use debug commands to monitor VLAN traffic and identify issues.

CLI Configuration for VLAN Setup on FortiGate

For network engineers who prefer using the CLI, FortiGate provides an easy way to configure VLANs using commands.

CLI Commands for VLAN Interface Setup:

config system interface
edit VLAN10
set vdom "root"
set ip 192.168.10.1/24
set allowaccess ping https ssh http
set interface "internal"  # Parent interface
set vlanid 10
next
end

This command creates a VLAN10 interface, assigns an IP address of 192.168.10.1/24, and associates it with the internal interface.

CLI Commands for Assigning VLAN to Physical Interfaces:

config system interface
edit VLAN10
set interface "internal"  # Parent interface
next
end

This command maps the VLAN10 interface to the internal physical interface.

CLI Commands for DHCP Configuration:

config system dhcp server
edit 1
set interface "VLAN10"
set lease-time 86400
config ip-range
edit 1
set start-ip 192.168.10.10
set end-ip 192.168.10.50
next
end
next
end

This command configures DHCP on VLAN10, with a lease range from 192.168.10.10 to 192.168.10.50.

CLI Commands for Firewall Policies:

config firewall policy
edit 0
set srcintf "VLAN10"
set dstintf "VLAN20"
set action accept
set schedule "always"
set service "ALL"
next
end

This command creates a firewall policy allowing traffic between VLAN10 and VLAN20.

CLI Commands for Inter-VLAN Routing:

config router static
edit 1
set gateway 192.168.10.1
set destination 192.168.20.0 255.255.255.0
next
end

This command sets up static routing to route traffic between VLAN10 and VLAN20.

CLI Commands for Troubleshooting:

diagnose debug enable
diagnose debug console timestamp enable
diagnose debug flow filter addr 192.168.10.1
diagnose debug flow trace start 100
diagnose debug application dns -1

These commands enable debugging for VLAN traffic and help in identifying network issues.

Conclusion

Configuring VLANs on a FortiGate firewall is crucial for segmenting network traffic, enhancing security, and improving performance. This complete guide provides both Web Interface and CLI-based configurations for VLAN setup, making it accessible to all types of users.

By following the steps outlined in this guide, you’ll be able to configure VLANs on your FortiGate firewall with ease. Additionally, troubleshooting tips, security best practices, and command-line examples will help you manage your VLANs effectively.