Cisco Firepower Threat Defense (FTD) VPN with AnyConnect

Overview

Duo MFA for Cisco Firepower Threat Defense (FTD) supports push, phone call, or passcode authentication for AnyConnect desktop and AnyConnect 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.

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 proxy service on a machine within your network. This Duo proxy server also acts as a RADIUS server — there's usually no need to deploy a separate RADIUS server to use Duo.

Next, locate (or set up) a system on which you will install the Duo Authentication Proxy. The proxy supports these operating systems:

• Windows Server 2012 or later (Server 2016 or 2019 recommended)
• CentOS 7 or later
• Red Hat Enterprise Linux 7 or later
• Ubuntu 16.04 or later
• Debian 7 or later.

Then you'll need to:

1. Sign up for a Duo account.
2. Log in to the Duo Admin Panel and navigate to Applications.
3. Click Protect an Application and locate Cisco Firepower Threat Defense VPN in the applications list. Click Protect to 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 in Duo and additional application options.

Install the Duo Authentication 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).

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. 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. In most cases, this means configuring the Proxy to communicate with Active Directory or RADIUS.

Active Directory

To use Active Directory/LDAP as your primary authenticator, add an [ad_client] section to the top of your config file. Add the following properties to the section:

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
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 when done.

Start the Proxy

net start DuoAuthProxy

net stop DuoAuthProxy & net start DuoAuthProxy

# /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.

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 → RADIUS Server Group 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 AnyConnect 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 can add a comma (",") to the end of your password, followed by a Duo passcode. For example, given a username 'bob', with password 'password123' and a Duo passcode '123456', you would enter:

username: bob
password: password123,123456

In addition, you may also enter the name of an out-of-band factor in lieu of a passcode. You may choose from the following factor names:

Returning to the previous example, if you wanted to use Duo Push (rather than a passcode) to authenticate, you would enter:

username: bob
password: password123,push

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 AnyConnect 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 AnyConnect.

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