Integrating OPNsense with Active Directory (AD) for IPsec VPNs can seem daunting, but trust me, guys, it's totally achievable and makes managing your VPN users a breeze! This setup lets you leverage your existing AD infrastructure to authenticate VPN clients, meaning no more juggling separate user databases. We will explore how to make this happen, ensuring a secure and streamlined VPN experience.

Why Integrate OPNsense with Active Directory for IPsec?

Before we dive in, let's talk about why you'd even want to do this. First off, centralized user management is a huge win. Instead of creating and managing VPN users directly on your OPNsense firewall, you can use your Active Directory. This simplifies things massively, especially in larger organizations. User accounts, passwords, and group memberships are all managed in one place. You can use AD groups to control VPN access, making it easy to grant or revoke access based on group membership. When a user leaves the company, disabling their AD account automatically revokes their VPN access. You get Enhanced Security too. Active Directory offers robust security features like password policies, account lockout, and Kerberos authentication, bolstering your VPN's security posture. Integrating with AD allows you to enforce these policies on VPN users.

Prerequisites

Okay, before we get our hands dirty, here's what you'll need:

• A working OPNsense firewall. Make sure your OPNsense installation is up and running.
• An Active Directory domain. You should have a functional Active Directory domain with users and groups.
• Network connectivity between OPNsense and your AD domain controllers. Ensure your OPNsense firewall can communicate with your Active Directory domain controllers.
• Basic understanding of OPNsense and Active Directory concepts. Familiarity with firewall rules, VPN configurations, and Active Directory user/group management will be helpful.

Step-by-Step Configuration

Alright, let's jump into the configuration. Follow these steps carefully, and you'll have your OPNsense firewall talking to your Active Directory in no time.

1. Configure LDAP Authentication in OPNsense

First, we need to set up OPNsense to authenticate against your Active Directory. This involves configuring LDAP (Lightweight Directory Access Protocol) settings.

• Navigate to System > Access > Servers in the OPNsense web interface.
• Click the + button to add a new authentication server.
• General Settings
  • Descriptive name: Give it a meaningful name, like "Active Directory".
  • Type: Select "LDAP".
  • Hostname: Enter the IP address or hostname of your Active Directory domain controller.
  • Port: The default LDAP port is 389 (or 636 for LDAPS). Use 389 unless you're using a secure connection.
  • Transport: Select "Plain" for standard LDAP or "SSL" for LDAPS (secure LDAP). Using SSL is highly recommended for security.
  • Security: check the TLS if you are using the default port.
  • Timeout: Default is fine.
• Authentication Container
  • Base DN: This is the base distinguished name for your Active Directory domain. For example, if your domain is "example.com," the Base DN might be "dc=example,dc=com".
  • Search scope: Set to "Subtree" to search the entire directory tree.
  • Bind DN: The distinguished name of an account with permissions to search Active Directory. This is often a dedicated service account. For example, "CN=OPNsense Bind,CN=Users,DC=example,DC=com".
  • Bind password: The password for the Bind DN account.
• User Settings
  • User DN: "CN=Users,DC=example,DC=com" or the container where your user accounts are stored.
  • Search scope: "Subtree"
  • Authentication method: "UserPrincipalName".
• Group Settings
  • Group DN: "CN=Groups,DC=example,DC=com" or the container where your group accounts are stored.
  • Search scope: "Subtree"
  • Group member attribute: "memberOf"
• Advanced Settings: Leave these at their defaults unless you have specific requirements.
• Click Save to save the LDAP server configuration.

2. Test the LDAP Configuration

Now, let's make sure OPNsense can actually talk to your Active Directory. Go to System > Access > Tester. Select your newly created LDAP server from the "Server" dropdown. Enter a username and password for an Active Directory user and click "Test". If everything is configured correctly, you should see a success message with the user's attributes.

3. Configure IPsec VPN

Next, we'll set up the IPsec VPN itself. This involves configuring the IKE (Internet Key Exchange) and IPsec settings.

• Navigate to VPN > IPsec > Tunnel Settings in the OPNsense web interface.
• Click the + button to add a new tunnel.
• General Settings
  • Disable this tunnel: Unchecked, to enable the tunnel.
  • Key exchange version: V2.
  • Internet Protocol: IPv4 or IPv6, depending on your network.
  • Interface: WAN or the interface connected to the internet.
  • Description: Give it a descriptive name, like "AD-IPsec-VPN".
• Phase 1 Proposal (Authentication)
  • Authentication method: EAP-MSCHAPv2. This is the crucial setting that enables Active Directory authentication.
  • Negotiation mode: Main.
  • My identifier: My IP Address. Set to your OPNsense firewall's WAN IP address.
  • Peer identifier: Peer IP Address. Set to a unique identifier for your VPN clients. This could be their IP address or a Fully Qualified Domain Name (FQDN).
  • Pre-shared Key: Leave blank when using EAP-MSCHAPv2.
• Phase 1 Proposal (Encryption)
  • Encryption algorithm: AES256 or a similarly strong algorithm.
  • Hash algorithm: SHA256 or a similarly strong algorithm.
  • DH key group: 14 (2048 bit).
• Phase 2 Proposal (SA/Key Exchange)
  • Protocol: ESP.
  • Encryption algorithms: AES256.
  • Hash algorithms: SHA256.
  • PFS key group: 14 (2048 bit).
• Phase 2 Proposal (Traffic Selectors)
  • Local Network: Your OPNsense firewall's internal network.
  • Remote Network: 0.0.0.0/0 to allow access to all networks (or specify specific networks).
• Advanced Settings
  • Automatically ping host: Optional. Enter an IP address to ping to keep the tunnel alive.
• Click Save to save the IPsec tunnel configuration.

4. Configure Firewall Rules

Now, you need to create firewall rules to allow traffic through the IPsec tunnel.

• Navigate to Firewall > Rules > IPsec in the OPNsense web interface.
• Click the + button to add a new rule.
• General Settings
  • Action: Pass.
  • Interface: IPsec.
  • Address Family: IPv4 or IPv6, depending on your network.
  • Protocol: Any.
• Source
  • Source: Any.
• Destination
  • Destination: Any.
• Description: Give the rule a descriptive name, like "Allow IPsec Traffic".
• Click Save to save the firewall rule.

5. Configure User Authentication

Now, let's configure the authentication settings for the VPN.

• Navigate to VPN > IPsec > Mobile Clients in the OPNsense web interface.

• Check the box Enable IPsec Mobile Client Support

• Authentication Settings

  • Server certificate: Select a certificate for authentication
  • Users: Select your Active Directory authentication server.

• Click Save to save the Mobile Clients configuration.

6. Client Configuration

Finally, you need to configure your VPN clients to connect to the OPNsense firewall. The configuration steps will vary depending on the client operating system.

• Windows: Use the built-in VPN client or a third-party client like OpenVPN. Configure the client to use IKEv2 and EAP-MSCHAPv2 for authentication. Provide the user's Active Directory username and password.
• macOS: Use the built-in VPN client. Configure the client to use IKEv2 and EAP-MSCHAPv2 for authentication. Provide the user's Active Directory username and password.
• Linux: Use a client like StrongSwan or OpenVPN. Configure the client to use IKEv2 and EAP-MSCHAPv2 for authentication. Provide the user's Active Directory username and password.

Troubleshooting

If you run into problems, here are a few things to check:

• LDAP Connectivity: Make sure your OPNsense firewall can reach your Active Directory domain controllers on ports 389 or 636. Use the tcpdump command on OPNsense to capture traffic and verify connectivity.
• Authentication Errors: Check the OPNsense system logs for authentication errors. These logs can provide clues about why authentication is failing.
• Firewall Rules: Double-check your firewall rules to make sure you're allowing traffic through the IPsec tunnel.
• Client Configuration: Verify that your VPN client is configured correctly with the correct settings for IKEv2, EAP-MSCHAPv2, and Active Directory credentials.

Final Thoughts

Integrating OPNsense with Active Directory for IPsec VPNs is a fantastic way to streamline user management and enhance security. While the initial setup might seem a bit involved, the long-term benefits are well worth the effort. By following these steps, you can create a secure and manageable VPN solution that leverages your existing Active Directory infrastructure. Remember to test your configuration thoroughly and consult the OPNsense documentation for more detailed information. Happy networking, folks!