Duo integrates with your Cisco Firepower Threat Defense (FTD) SSL VPN to add two-factor authentication to AnyConnect VPN logins.
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.
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.
This application communicates with Duo's service on TCP port 443. Firewall configurations that restrict outbound access to Duo's service with rules using destination IP addresses or IP address ranges aren't recommended, since these may change over time to maintain our service's high availability. If your organization requires IP-based rules, please review this Duo KB article.
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.
If you will set up a new Duo server, locate (or set up) a system to host the Duo Authentication Proxy installation. The proxy supports these operating systems:
See detailed Authentication Proxy operating system performance recommendations in the Duo Authentication Proxy Reference.
Then you'll need to:
The security of your Duo application is tied to the security of your secret key (skey). Secure it as you would any sensitive credential. Don't share it with unauthorized individuals or email it to anyone under any circumstances!
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.
When installing, you can choose whether or not you want to install the Proxy Manager. The Proxy Manager is a Windows utility that helps you edit the Duo Authentication Proxy configuration, determine the proxy's status, and start or stop the proxy service. Learn more about using the Proxy Manager. Installing the Proxy Manager adds about 100 MB to the installed size.
If you do not want to install the Proxy Manager, you may deselect it on the "Choose Components" installer screen before clicking Install.
To perform a silent install on Windows, issue the following from an elevated command prompt after downloading the installer (replacing version with the actual version you downloaded):
/exclude-auth-proxy-manager to install silently without the Proxy Manager:
duoauthproxy-version.exe /S /exclude-auth-proxy-manager
Ensure that Perl and a compiler toolchain are installed. On most recent RPM-based distributions — like Fedora, RedHat Enterprise, and CentOS — you can install these by running (as root):
$ yum install gcc make libffi-devel perl zlib-devel diffutils
On Debian-derived systems, install these dependencies by running (as root):
$ apt-get install build-essential libffi-dev perl zlib1g-dev
If SELinux is present on your system and you want the Authentication Proxy installer to build and install its SELinux module, include
selinux-policy-devel in the dependencies:
$ yum install gcc make libffi-devel perl zlib-devel diffutils selinux-policy-devel
$ apt-get install build-essential libffi-dev perl zlib1g-dev selinux-policy-devel
Download the most recent Authentication Proxy for Unix from https://dl.duosecurity.com/duoauthproxy-latest-src.tgz. From the command line you can use
wget to download the file, like
$ wget --content-disposition https://dl.duosecurity.com/duoauthproxy-latest-src.tgz. Depending on your download method, the actual filename may reflect the version e.g. duoauthproxy-5.7.3-src.tgz. View checksums for Duo downloads here.
Extract the Authentication Proxy files and build it as follows:
$ tar xzf duoauthproxy-5.7.3-src.tgz $ cd duoauthproxy-version-src $ make
Install the authentication proxy (as root):
$ cd duoauthproxy-build $ ./install
Follow the prompts to complete the installation. The installer creates a user to run the proxy service and a group to own the log directory and files. You can accept the default user and group names or enter your own.
If SELinux is present on the target server, the Duo installer will ask you if you want to install the Authentication Proxy SELinux module. Your selection affects whether systemd can start the Authentication Proxy after installation.
|SELinux Mode||Default Response||Result|
|Enforcing||Yes||Choose 'yes' to install the Authentication Proxy's SELinux module. This permits start of the Authentication Proxy service by systemd. If you choose 'no' then the SELinux module is not installed, and systemd cannot start the Authentication Proxy service.|
|Permissive||No||Choose 'no' to decline install of the Authentication Proxy's SELinux module. The Authentication Proxy service can be started by systemd. However, if you change SELinux from permissive to enforcing mode after installing the Duo proxy, systemd can no longer start the Authentication Proxy service. If you plan to enable SELinux enforcing mode later, you should choose 'yes' to install the Authentication Proxy SELinux module now.|
To install the Duo proxy silently with the default options, use the following command:
sudo ./duoauthproxy-build/install --install-dir /opt/duoauthproxy --service-user duo_authproxy_svc --log-group duo_authproxy_grp --create-init-script yes
--enable-selinux=yes|no to the install command to choose whether to install the Authentication Proxy SELinux module.
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:
|Windows||v5.0.0 and later||
|Windows||v4.0.2 and earlier||
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:
Individual properties beneath a section appear as:
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.
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:
%ProgramFiles%\Duo Security Authentication Proxy\conf\authproxy.cfgfile 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.
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.
[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:
The hostname or IP address of your domain controller or directory server. If this host doesn't respond to a primary authentication request and no additional hosts are specified (as
The username of a domain account that has permission to bind to your directory and perform searches. We recommend creating a service account that has read-only access.
The password corresponding to
The LDAP distinguished name (DN) of an Active Directory/LDAP container or organizational unit (OU) containing all of the users you wish to permit to log in. For example:
The hostname or IP address of a secondary/fallback domain controller or directory server, which the Authentication Proxy will use if a primary authentication request to the system defined as
To further restrict access, specify the LDAP distinguished name (DN) of a security group that contains the users who should be able to log in as direct group members. Nested groups are not supported. Users who are not direct members of the specified group will not pass primary authentication. Example:
Starting with Authentication Proxy v3.2.0, the
LDAP attribute found on a user entry which will contain the submitted username. In most Active Directory configurations, it should not be necessary to change this option from the default value. OpenLDAP directories may use "uid" or another attribute for the username, which should be specified with this option.
[ad_client] host=184.108.40.206 host_2=220.127.116.11 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.
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:
The IP address of your primary RADIUS server. If this host doesn't respond to a primary authentication request and no additional hosts are specified (as
A secret to be shared between the Authentication Proxy and your existing RADIUS server. If you installed the Duo proxy on Windows and would like to encrypt this secret, see Encrypting Passwords in the full Authentication Proxy documentation.
The hostname or IP address of a secondary/fallback primary RADIUS server, which the Authentication Proxy will use if a primary authentication request to the system defined as
The authentication port on your RADIUS server. Use
If this option is set to
[radius_client] host=18.104.22.168 host_2=22.214.171.124 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.
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
Your Duo integration key, obtained from the details page for the application in the Duo Admin Panel.
Your Duo secret key, obtained from the details page for the application in the Duo Admin Panel. If you're on Windows and would like to encrypt the skey, see Encrypting Passwords in the full Authentication Proxy documentation.
Your Duo API hostname (e.g.
The IP address of your Cisco FTD SSL VPN. Only clients with configured addresses and shared secrets will be allowed to send requests to the Authentication Proxy.
A secret to be shared between the proxy and your Cisco FTD SSL VPN. If you're on Windows and would like to encrypt this secret, see Encrypting Passwords in the full Authentication Proxy documentation.
The mechanism that the Authentication Proxy should use to perform primary authentication. This should correspond with a "client" section elsewhere in the config file.
This parameter is optional if you only have one "client" section. If you have multiple, each "server" section should specify which "client" to use.
Port on which to listen for incoming RADIUS Access Requests. If you have multiple RADIUS server sections you should use a unique port for each one.
The IP address of your second Cisco FTD SSL VPN, if you have one. You can specify additional devices as as
The secrets shared with your second Cisco FTD SSL VPN, if using one. You can specify secrets for additional devices as
Comma-separated list of additional RADIUS attributes to pass through from the primary authentication to the device integrating with the Authentication Proxy when authentication is accepted. The attribute must exist in the Authentication Proxy's RADIUS dictionary. The dictionary includes standard RADIUS attributes, as well as some vendor specific attributes from Cisco, Juniper, Microsoft, and Palo Alto. If it is not known whether the dictionary includes the specific RADIUS attribute you wish to send, use
Only valid when used with
If this option is set to "true", all RADIUS attributes set by the primary authentication server will be copied into RADIUS responses sent by the proxy. Only valid when used with
A completed config file that uses Active Directory should look something like:
[ad_client] host=126.96.36.199 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=188.8.131.52 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.
If you installed the Duo Authentication Proxy Manager utility (available with 5.6.0 and later), click the Start Service button at the top of the Proxy Manager window to start the service.
To start the service from the command line, open an Administrator command prompt and run:
net start DuoAuthProxy
Alternatively, open the Windows Services console (
services.msc), locate "Duo Security Authentication Proxy Service" in the list of services, and click the Start Service button.
Authentication Proxy v5.1.0 and later includes the
authproxyctl executable, which shows the connectivity tool output when starting the service. The installer adds the Authentication Proxy
C:\Program Files\Duo Security Authentication Proxy\bin to your system path automatically, so you should not need to specify the full path to
authproxyctl to run it.
From an administrator command prompt run:
If the service starts successfully, Authentication Proxy service output is written to the authproxy.log file, which can be found in the
If you see an error saying that the "service could not be started", open the Application Event Viewer and look for an Error from the source "DuoAuthProxy". The traceback may include a "ConfigError" that can help you find the source of the issue.
Stop and restart the Authentication Proxy service by either clicking the Restart Service button in the Duo Authentication Proxy Manager or the Windows Services console or issuing these commands from an Administrator command prompt:
net stop DuoAuthProxy & net start DuoAuthProxy
To stop and restart the Authentication Proxy using authproxyctl, from an administrator command prompt run:
Open a root shell and run:
# /opt/duoauthproxy/bin/authproxyctl start
To ensure the proxy started successfully, run:
# /opt/duoauthproxy/bin/authproxyctl status
Authentication Proxy service output is written to the authproxy.log file, which can be found in the
To stop and restart the Authentication Proxy, open a root shell and run:
# /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.
Log into the FMC console that manages your FTD SSL VPN devices.
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.
Fill out the "Add RADIUS Server Group" form:
|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.|
In the "RADIUS Servers" section of the form, click the green plus sign to add a RADIUS server.
Fill out the "New RADIUS Server" form:
|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
|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.|
Once you have added the Duo RADIUS server to the group, click Save to create the new Duo RADIUS server group.
Navigate to Devices → VPN → Remote Access.
Click on the VPN configuration to which you want to add Duo.
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.
Once on the "Edit Connection Profile" form, click the AAA tab.
Change the "Authentication Server" from the existing selection to the Duo RADIUS server group you created earlier.
You typically do not need to select an "Authorization Server" or "Accounting Server".
Do not configure the "Password Management" options.
Click the Save button on the "Edit Connection Profile" form
Click the Save button in the upper right of the FMC console window (where it says "You have unsaved changes").
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 may add a comma (",") to the end of your password and append a Duo factor option:
|push||Perform Duo Push authentication. You can use Duo Push if you've installed and activated Duo Mobile on your device.|
|phone||Perform phone callback authentication.|
|sms||Send a new batch of SMS passcodes. Your authentication attempt will be denied. You can then authenticate with one of the newly-delivered passcodes.|
|A numeric passcode||Log in using a passcode, either generated with Duo Mobile, sent via SMS, generated by your hardware token, or provided by an administrator. Examples: "123456" or "2345678".|
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 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.
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.