Duo Two-Factor Authentication for Cisco Firepower Threat Defense (FTD) VPN with Secure Client

Overview

Duo MFA for Cisco Firepower Threat Defense (FTD) supports push, phone call, or passcode authentication for Secure Client desktop and Secure Client mobile client VPN connections that use SSL encryption. This configuration does not feature the interactive Duo Prompt for web-based logins, but does capture client IP information for use with Duo policies, such as geolocation and authorized networks.

These instructions walk you through adding two-factor authentication via RADIUS to your FTD using the Firepower Management Center (FMC) console. The instructions also assume you already have a functioning FTD Remote Access SSL VPN deployment using an existing AAA authentication server (like an on-premises AD/LDAP directory).

Duo supports RADIUS 2FA configuration starting with FTD and FMC versions 6.3.0.

The SAML VPN instructions for Firepower 6.7 and later feature inline enrollment and the interactive Duo Prompt for both web-based VPN logins and AnyConnect 4.6+ client logins. This deployment option features Duo Single Sign-On, our cloud-hosted SAML 2.0 identity provider. Primary and Duo secondary authentication occur at the identity provider, not at the ASA itself.

Walkthrough Video

First Steps

Before moving on to the deployment steps, it's a good idea to familiarize yourself with Duo administration concepts and features like options for applications, available methods for enrolling Duo users, and Duo policy settings and how to apply them. See all Duo Administrator documentation.

You should already have a working primary authentication configuration for your Cisco FTD SSL VPN users before you begin to deploy Duo.

To integrate Duo with your Cisco FTD SSL VPN, you will need to install a local Duo proxy service on a machine within your network. This Duo proxy server will receive incoming RADIUS requests from your Cisco FTD SSL VPN, contact your existing local LDAP/AD or RADIUS server to perform primary authentication, and then contact Duo's cloud service for secondary authentication.

If you are already running a Duo Authentication Proxy server in your environment, you can use that existing host for additional applications, appending the new configuration sections to the current config. You don't have to set up a new Authentication Proxy server for each application you create. However, there are some cases where it might make sense for you to deploy a new proxy server for a new application, like if you want to co-locate the Duo proxy with the application it will protect in the same data center.

We recommend the following 64-bit operating systems for the system hosting the Duo Authentication Proxy:

• Windows Server 2016 or later
• CentOS Stream 9 or later
• Fedora 39 or later
• Red Hat Enterprise Linux 7 or later
• Rocky Linux 9 or later
• Ubuntu 20.04 LTS or later
• Debian 11 or later

The Duo End of Sale, Last Date of Support, and End of Life Policy states that Duo does not offer support for integrations running on operating system versions beyond the vendor’s stated Last Date of Support date.

See detailed Authentication Proxy operating system performance recommendations in the Duo Authentication Proxy Reference.

We do not recommend installing the Duo Authentication Proxy on the same Windows server that acts as your Active Directory domain controller or one with the Network Policy Server (NPS) role. If you must co-locate the Duo Authentication Proxy with these services, be prepared to resolve potential LDAP or RADIUS port conflicts between the Duo service and your pre-existing services.

Then you'll need to:

1. Sign up for a Duo account.
2. Log in to the Duo Admin Panel and navigate to Applications → Application Catalog.
3. Locate the entry for Cisco Firepower Threat Defense VPN with the "2FA" label in the catalog. Click the Add button to create the application and get your integration key, secret key, and API hostname. You'll need this information to complete your setup. See Protecting Applications for more information about protecting applications with Duo and additional application options.
4. No users can log in to new applications until you grant access. Update the User access setting to grant access to this application to users in selected Duo groups, or to all users. Learn more about user access to applications. If you do not change this setting now, be sure to update it so that your test user has access before you test your setup.

Install the Duo Authentication Proxy

If you will reuse an existing Duo Authentication Proxy server for this new application, you can skip the install steps and go to Configure the Proxy.

The Duo Authentication Proxy can be installed on a physical or virtual host. We recommend a system with at least 1 CPU, 200 MB disk space, and 4 GB RAM (although 1 GB RAM is usually sufficient). See additional Authentication Proxy performance recommendations in the Duo Authentication Proxy Reference.

We do not recommend installing the Duo Authentication Proxy on the same Windows server that acts as your Active Directory domain controller or one with the Network Policy Server (NPS) role. If you must co-locate the Duo Authentication Proxy with these services, be prepared to resolve potential LDAP or RADIUS port conflicts between the Duo service and your pre-existing services.

duoauthproxy-version.exe /S

duoauthproxy-version.exe /S /exclude-auth-proxy-manager

sudo ./duoauthproxy-build/install --install-dir /opt/duoauthproxy --service-user duo_authproxy_svc --log-group duo_authproxy_grp --create-init-script yes

Configure the Proxy

After the installation completes, you will need to configure the proxy.

The Duo Authentication Proxy configuration file is named authproxy.cfg, and is located in the conf subdirectory of the proxy installation. With default installation paths, the proxy configuration file will be located at:

Note that as of v4.0.0, the default file access on Windows for the conf directory is restricted to the built-in Administrators group during installation.

The configuration file is formatted as a simple INI file. Section headings appear as:

[section]

Individual properties beneath a section appear as:

name=value

The Authentication Proxy may include an existing authproxy.cfg with some example content. For the purposes of these instructions, however, you should delete the existing content and start with a blank text file.

Duo Authentication Proxy Manager

The Duo Authentication Proxy Manager is a Windows utility for managing the Authentication Proxy installation on the Windows server where you install the Authentication Proxy. The Proxy Manager comes with Duo Authentication Proxy for Windows version 5.6.0 and later.

The Proxy Manager cannot manage remote Duo Authentication Proxy servers, nor can you install the Proxy Manager as a stand-alone application. There is no Proxy Manager available for Linux. The Proxy Manager only functions as part of a local Duo Authentication Proxy installation on Windows servers.

Learn more about using the Proxy Manager in the Duo Authentication Proxy Reference before you continue.

To launch the Proxy Manager utility:

• Open the Start Menu and go to Duo Security.
• Click the Duo Authentication Proxy Manager icon to launch the application. You must have administrative privileges on the Windows server and accept the prompt for elevation.
• The Proxy Manager launches and automatically opens the %ProgramFiles%\Duo Security Authentication Proxy\conf\authproxy.cfg file for editing.

Use the Proxy Manager editor on the left to make the authproxy.cfg changes in these instructions. As you type into the editor, the Proxy Manager will automatically suggest configuration options. Accepting these suggestions helps make sure you use the correct option syntax.

As you follow the instructions on this page to edit the Authentication Proxy configuration, you can click Validate to verify your changes (output shown on the right).

When you complete the Authentication Proxy configuration steps in this document, you can use the Save button to write your updates to authproxy.cfg, and then use the authproxy.cfg button to start the Authentication Proxy service before continuing on to the next configuration steps.

If you do not use the Proxy Manager to edit your configuration then we recommend using WordPad or another text editor instead of Notepad when editing the config file on Windows.

Configure the Proxy for Your Primary Authenticator

In this step, you'll set up the Proxy's primary authenticator — the system which will validate users' existing passwords. Determine which type of primary authentication you'll be using, and create either an Active Directory/LDAP [ad_client] client section, or a RADIUS [radius_client] section as follows.

Active Directory

Add an [ad_client] section if you'd like to use an Active Directory domain controller (DC) or LDAP-based directory server to perform primary authentication. This section accepts the following options:

Required

search_dn=DC=example,DC=com

Optional

security_group_dn=CN=DuoVPNUsers,OU=Groups,DC=example,DC=com

For example:

[ad_client]
host=1.2.3.4
host_2=1.2.3.5
service_account_username=duoservice
service_account_password=password1
search_dn=DC=example,DC=com
security_group_dn=CN=DuoVPNUsers,OU=Groups,DC=example,DC=com

For advanced Active Directory configuration, see the full Authentication Proxy documentation.

RADIUS

To use RADIUS as your primary authenticator, add a [radius_client] section to the top of your config file. Then add the following properties to the section:

Required

Optional

For example:

[radius_client]
host=1.2.3.4
host_2=1.2.3.5
secret=radiusclientsecret

In addition, make sure that the RADIUS server is configured to accept authentication requests from the Authentication Proxy.

For advanced RADIUS configuration, see the full Authentication Proxy documentation.

Configure the Proxy for Your Cisco FTD SSL VPN

Next, we'll set up the Authentication Proxy to work with your Cisco FTD SSL VPN. Create a [radius_server_auto] section and add the properties listed below. If you've already set up the Duo Authentication Proxy for a different RADIUS Auto application, append a number to the section header to make it unique, like [radius_server_auto2].

Required

Optional

A completed config file that uses Active Directory should look something like:

[ad_client]
host=1.2.3.4
service_account_username=duoservice
service_account_password=password1
search_dn=cn=Users,dc=example,dc=com
 
[radius_server_auto]
ikey=DIXXXXXXXXXXXXXXXXXX
skey=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
api_host=api-XXXXXXXX.duosecurity.com
radius_ip_1=5.6.7.8
radius_secret_1=radiussecret1
client=ad_client
port=1812
failmode=safe

Make sure to save your configuration file in your text editor — or validate and save in the Proxy Manager for Windows — when you're finished making changes.

Start the Proxy

net start DuoAuthProxy

authproxyctl start

net stop DuoAuthProxy & net start DuoAuthProxy

authproxyctl restart

# /opt/duoauthproxy/bin/authproxyctl start

# /opt/duoauthproxy/bin/authproxyctl status

# /opt/duoauthproxy/bin/authproxyctl restart

If you modify your authproxy.cfg configuration after initial setup, you'll need to stop and restart the Duo Authentication Proxy service or process for your change to take effect.

You can view information about your Authentication Proxy in the Authentication Proxy Dashboard.

Configure Your Cisco FTD using FMC

Add the Duo RADIUS server

1. Log into the FMC console that manages your FTD SSL VPN devices.

2. Navigate to Objects → Object Management → AAA Server* → RADIUS Server Group (or Objects → Object Management → RADIUS Server Group depending on your Firepower version) and click Add RADIUS Server Group.

3. Fill out the "Add RADIUS Server Group" form:

   Setting	Value
   Name	Something descriptive, like "DuoRADIUS". You may not enter a name containing a space.
   Description	Some informative text.
   Group Accounting Mode	Leave as Single.
   Retry Interval	Leave as 10.
   Realms	No need to select a realm.
   Enable authorize only Enable interim account update Enable dynamic authorization	Do not enable.

4. In the "RADIUS Servers" section of the form, click the green plus sign to add a RADIUS server.

5. Fill out the "New RADIUS Server" form:

   Setting	Value
   IP Address/Hostname	The fully-qualified hostname or IP address of your Duo Authentication Proxy server.
   Authentication Port	1812 (or whichever port you specified in your authproxy.cfg file).
   Key	The exact shared secret used in your Authentication Proxy configuration.
   Confirm Key	Re-enter the shared secret.
   Server Accounting Port	Defaults to 1813 (this value does not matter because the Duo Authentication Proxy does not support RADIUS Accounting).
   Timeout	60 seconds should be sufficient to complete authentication.
   Connect using	Select either "Routed" or "Specific Interface" and make a selection. Your choice here depends on how connectivity is established from the FTD to the Duo RADIUS AAA server. See the "RADIUS Server Options" section in chapter 18 of the Firepower Management Center Configuration Guide, Version 6.3 for more information, or here in the online FMC 6.3 guide. In this example, routing is used.
   Redirect ACL	Select or add the redirect ACL (only if using FTD with ISE). See the "RADIUS Server Options" section in chapter 18 of the Firepower Management Center Configuration Guide, Version 6.3 for more information, or here in the online FMC 6.3 guide. In this example, ISE ACLs aren't used.

   

6. Once you have added the Duo RADIUS server to the group, click Save to create the new Duo RADIUS server group.

   

Change the Remote Access VPN Authentication Method to Duo RADIUS

1. Navigate to Devices → VPN → Remote Access.

2. Click on the VPN configuration to which you want to add Duo.

3. While viewing the "Connection Profiles" tab for the selected VPN configuration, click the pencil icon on the far right to edit the connection profile that you want to start using the Duo RADIUS AAA server group.

4. Once on the "Edit Connection Profile" form, click the AAA tab.

5. Change the "Authentication Server" from the existing selection to the Duo RADIUS server group you created earlier.

6. You typically do not need to select an "Authorization Server" or "Accounting Server".

7. Do not configure the "Password Management" options.

8. Click the Save button on the "Edit Connection Profile" form

   

9. Click the Save button in the upper right of the FMC console window (where it says "You have unsaved changes").

Deploy Changes to FTD devices

1. Click the Deploy button in the top right of the FMC site.
2. Select the FTD device (or devices) to which you want to push the new Remote Access VPN config with Duo.
3. Click the Deploy button.
4. Watch for the deployment to complete with the status "Deployment to device successful".

Test Your Setup

Launch the client and select the VPN profile that now uses Duo RADIUS authentication.

To test your setup, attempt to log in to your newly-configured system as a user enrolled in Duo with an authentication device.

When you enter your username and password, you will receive an automatic push or phone callback.

Alternatively you may add a comma (",") to the end of your password and append a Duo factor option:

For example, if you wanted to use a passcode to authenticate instead of Duo Push or a phone call, you would enter:

username: bob
password: hunter2,123456

If you wanted to use specify use of phone callback to authenticate instead of an automatic Duo Push request, you would enter:

username: bob
password: hunter2,phone

You can also specify a number after the factor name if you have more than one device enrolled (as the automatic push or phone call goes to the first capable device attached to a user). So you can enter phone2 or push2 if you have two phones enrolled and you want the authentication request to go to the second phone.

Once you approve the Duo authentication request (or if you appended a valid passcode to your password for MFA), the client is connected to the VPN.

Logging into the web-based VPN via browser sends an automatic Duo request via push or phone call. You can also append a different Duo factor name or passcode to your password in the browser, just like you can in Secure Client.

Grant Access to Users

If you did not already grant user access to the Duo users you want to use this application be sure to do that before inviting or requiring them to log in with Duo.

Troubleshooting

Need some help? Review troubleshooting tips for the Authentication Proxy and try the connectivity tool included with Duo Authentication Proxy 2.9.0 and later to discover and troubleshoot general connectivity issues.

Also take a look at the Cisco Frequently Asked Questions (FAQ) page or try searching our Cisco Knowledge Base articles or Community discussions. For further assistance, contact Support.

Network Diagram

1. Primary authentication initiated to Cisco FTD
2. Cisco FTD sends authentication request to the Duo Authentication Proxy
3. Primary authentication using Active Directory or RADIUS
4. Duo Authentication Proxy connection established to Duo Security over TCP port 443
5. Secondary authentication via Duo Security’s service
6. Duo Authentication Proxy receives authentication response
7. Cisco FTD VPN access granted