Setting up a secure site-to-site VPN using FortiGate firewalls and the IPsec protocol with IKEv2 for key exchange is crucial for businesses needing to connect multiple networks securely. IPsec IKEv2 FortiGate configuration provides enhanced security, improved stability, and better performance compared to older VPN protocols. This guide simplifies the process, making it accessible even if you're not a networking guru. We'll walk through each step, ensuring you can create a robust and reliable VPN tunnel between your sites.

Understanding the Basics

Before diving into the configuration, let's cover some fundamental concepts. A site-to-site VPN allows two or more networks to communicate securely over the internet. Think of it as creating a private, encrypted tunnel between your offices or data centers. IPsec (Internet Protocol Security) is a suite of protocols that provides this secure communication, while IKEv2 (Internet Key Exchange version 2) handles the secure negotiation of the encryption keys used by IPsec. IKEv2 is preferred over its predecessor, IKEv1, due to its improved security features, faster connection times, and better handling of network changes.

Why Choose IKEv2? IKEv2 offers several advantages, including enhanced security with stronger encryption algorithms and better protection against attacks. It also provides improved stability, maintaining connections even when network conditions fluctuate. Additionally, IKEv2 supports features like Dead Peer Detection (DPD), which helps detect and recover from VPN tunnel failures quickly. All these factors contribute to a more reliable and secure VPN connection.

FortiGate's Role: FortiGate firewalls are popular choices for businesses due to their comprehensive security features and ease of management. They provide a robust platform for implementing IPsec VPNs, with a user-friendly interface and extensive configuration options. By using FortiGate firewalls at each site, you can create a secure and reliable VPN tunnel that protects your data and ensures seamless communication between your networks.

Prerequisites

Before you start configuring your FortiGate firewalls, make sure you have the following:

• Two FortiGate firewalls: One at each site you want to connect.
• Public IP addresses: Each FortiGate must have a static public IP address.
• FortiGate access: You need administrative access to both FortiGate firewalls.
• Network information: Have the subnet details for each network you're connecting.

Configuration Steps

Now, let's get down to the nitty-gritty. We'll configure the IPsec IKEv2 VPN on both FortiGate firewalls step by step.

Step 1: Configure the IPsec Phase 1 Settings

Phase 1 defines how the two FortiGate firewalls will authenticate and establish a secure channel for further communication. This involves setting up the IKEv2 parameters.

1. Log in to your FortiGate firewall. Use your web browser to access the FortiGate's management interface.
2. Navigate to VPN > IPsec Tunnels and click 'Create New > IPsec Tunnel'. This will start the VPN creation wizard.
3. Name your VPN tunnel. Give it a descriptive name, such as 'SiteA-to-SiteB'.
4. Select 'Custom' as the template type. This allows you to configure the settings manually.
5. Under 'Authentication', choose 'IKEv2'.
6. Set the 'IP Version' to IPv4.
7. Choose the 'Interface'. Select the interface that connects to the internet (usually 'wan1' or 'port1').
8. Set the 'Remote Gateway' to 'Static IP Address' and enter the public IP address of the remote FortiGate.
9. Set the 'Authentication Method' to 'Pre-shared Key'.
10. Enter a strong pre-shared key. Make sure to use the same pre-shared key on both FortiGate firewalls. This key is like a password that both sides need to know.
11. Under 'IKEv2 Parameters', configure the following:
    • 'Encryption': Choose a strong encryption algorithm like AES256.
    • 'Authentication': Select SHA256.
    • 'Diffie-Hellman Group': Choose a strong group like 14 (2048-bit MODP).
    • 'Key Lifetime': Set the key lifetime to 28800 seconds (8 hours).
12. Enable 'Dead Peer Detection (DPD)'. This helps detect if the remote FortiGate is unresponsive.
    • 'DPD Interval': Set the DPD interval to 5 seconds.
    • 'DPD Retry': Set the DPD retry to 3 times.
13. Click 'OK' to save the Phase 1 settings.

Step 2: Configure the IPsec Phase 2 Settings

Phase 2 defines how the data will be encrypted and protected as it passes through the VPN tunnel. This involves setting up the IPsec parameters.

1. In the VPN tunnel configuration, navigate to 'Phase 2 Selectors'.
2. Click 'Create New'.
3. Name the Phase 2 selector. Give it a descriptive name like 'SiteA-to-SiteB-Phase2'.
4. Under 'Proposal', configure the following:
   • 'Protocol': Choose ESP (Encapsulating Security Payload).
   • 'Encryption': Select a strong encryption algorithm like AES256.
   • 'Authentication': Choose SHA256.
   • 'PFS (Perfect Forward Secrecy)': Enable PFS and select the same Diffie-Hellman group you used in Phase 1 (e.g., 14).
   • 'Key Lifetime': Set the key lifetime to 3600 seconds (1 hour).
5. Under 'Selectors', define the local and remote subnets that will be allowed to communicate through the VPN tunnel.
   • 'Local Address': Enter the subnet of your local network (e.g., 192.168.1.0/24).
   • 'Remote Address': Enter the subnet of the remote network (e.g., 192.168.2.0/24).
6. Click 'OK' to save the Phase 2 settings.

Step 3: Create Static Routes

To ensure traffic is routed correctly through the VPN tunnel, you need to create static routes on both FortiGate firewalls.

1. Navigate to 'Network > Static Routes'.
2. Click 'Create New'.
3. 'Destination': Enter the remote network's subnet (e.g., 192.168.2.0/24).
4. 'Gateway': Select the IPsec tunnel you created earlier (e.g., 'SiteA-to-SiteB').
5. 'Distance': Set the administrative distance (usually 10).
6. Click 'OK' to save the static route.
7. Repeat these steps on the other FortiGate firewall, but with the local and remote subnets reversed.

Step 4: Create Firewall Policies

Firewall policies control which traffic is allowed to pass through the VPN tunnel. You need to create policies that allow traffic between the local and remote networks.

1. Navigate to 'Policy & Objects > Firewall Policy'.
2. Click 'Create New'.
3. Configure the following settings:
   • 'Name': Give the policy a descriptive name (e.g., 'SiteA-to-SiteB-Policy').
   • 'Incoming Interface': Select the interface connected to your local network (e.g., 'lan').
   • 'Outgoing Interface': Select the IPsec tunnel you created (e.g., 'SiteA-to-SiteB').
   • 'Source Address': Specify the local network's subnet (e.g., 192.168.1.0/24).
   • 'Destination Address': Specify the remote network's subnet (e.g., 192.168.2.0/24).
   • 'Schedule': Set the schedule to 'always'.
   • 'Service': Choose the services you want to allow (e.g., 'ALL', 'ICMP', 'HTTPS').
   • 'Action': Set the action to 'ACCEPT'.
4. Enable NAT if needed. If your local network uses private IP addresses, you may need to enable NAT (Network Address Translation) on the outgoing interface.
5. Click 'OK' to save the firewall policy.
6. Repeat these steps to create a policy for traffic going from the remote network to the local network. Reverse the source and destination addresses and select the appropriate interfaces.

Verification

Once you've configured both FortiGate firewalls, it's time to verify that the VPN tunnel is working correctly.

1. Navigate to 'VPN > IPsec Monitor'.
2. Check the status of the IPsec tunnel. It should show as 'UP'.
3. Ping a device on the remote network from a device on the local network. If the ping is successful, the VPN tunnel is working correctly.
4. Test other services that you've allowed through the firewall policies. For example, try accessing a web server on the remote network.

Troubleshooting

If you encounter issues, here are some common troubleshooting steps:

• Check the IPsec tunnel status: Make sure the tunnel is up and active.
• Verify the pre-shared key: Ensure the pre-shared key is the same on both FortiGate firewalls. Even a small typo can prevent the VPN from working.
• Check the firewall policies: Make sure the policies are configured correctly and allow the necessary traffic.
• Review the static routes: Verify that the static routes are pointing to the correct subnets and IPsec tunnel.
• Examine the FortiGate logs: The logs can provide valuable information about any errors or issues.
• Use the 'execute ping' and 'execute traceroute' commands: These commands can help you diagnose network connectivity issues.

Security Considerations

While IPsec IKEv2 provides a secure VPN connection, it's essential to follow security best practices to protect your network.

• Use strong pre-shared keys: Choose a pre-shared key that is long, complex, and difficult to guess.
• Keep your FortiGate firmware up to date: Regularly update your FortiGate firewalls to the latest firmware to patch any security vulnerabilities.
• Monitor your VPN tunnel: Keep an eye on the VPN tunnel status and logs to detect any suspicious activity.
• Implement strong password policies: Enforce strong password policies for all users on your network.
• Use multi-factor authentication: Enable multi-factor authentication for administrative access to your FortiGate firewalls.

Conclusion

Setting up an IPsec IKEv2 FortiGate site-to-site VPN might seem daunting at first, but by following these steps, you can create a secure and reliable connection between your networks. This guide provides a comprehensive overview of the configuration process, from understanding the basics to troubleshooting common issues. Remember to prioritize security and follow best practices to protect your network from threats. With a properly configured IPsec VPN, you can ensure that your data is safe and your networks can communicate seamlessly. So go ahead, give it a try, and enjoy the peace of mind that comes with a secure VPN connection! Guys, you totally got this! Happy networking!