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.
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 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:
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!
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).
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-develOn Debian-derived systems, install these dependencies by running (as root):
$ apt-get install build-essential libffi-dev perl zlib1g-devDownload the most recent Authentication Proxy for Unix from https://dl.duosecurity.com/duoauthproxy-latest-src.tgz. Depending on your download method, the actual filename may reflect the version e.g. duoauthproxy-5.1.0-src.tgz. View checksums for Duo downloads here.
Extract the Authentication Proxy files and build it as follows:
$ tar xzf duoauthproxy-latest-src.tgz
$ cd duoauthproxy-version-src
$ makeInstall the authentication proxy (as root):
$ cd duoauthproxy-build
$ ./installFollow 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 you ever need to uninstall the proxy, run /opt/duoauthproxy/uninstall.
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:
| Operating System | Authentication Proxy Version |
Path |
|---|---|---|
| Windows | v5.0.0 and later | C:\Program Files\Duo Security Authentication Proxy\conf\authproxy.cfg |
| Windows | v4.0.2 and earlier | C:\Program Files (x86)\Duo Security Authentication Proxy\conf\authproxy.cfg |
| Linux | All | /opt/duoauthproxy/conf/authproxy.cfg |
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=valueThe 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.
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.
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
host
|
The hostname or IP address of your domain controller. |
service_account_username
|
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. |
service_account_password
|
The password corresponding to |
search_dn
|
The LDAP distinguished name (DN) of an Active Directory container or organizational unit (OU) containing all of the users you wish to permit to log in. For example: |
Optional
host_2
|
The hostname or IP address of a secondary/fallback domain controller. You can add additional domain controllers as |
security_group_dn
|
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 |
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=comFor 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:
Required
host
|
The IP address of your RADIUS server. You can add backup servers with |
secret
|
A secret to be shared between the Authentication Proxy and your existing RADIUS server. If you're on Windows and would like to encrypt this secret, see Encrypting Passwords in the full Authentication Proxy documentation. |
Optional
port
|
The authentication port on your RADIUS server. Use Default: |
pass_through_all
|
If this option is set to Default: |
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.
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
ikey
|
Your Duo integration key, obtained from the details page for the application in the Duo Admin Panel. |
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skey
|
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. |
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api_host
|
Your Duo API hostname (e.g. |
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radius_ip_1
|
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. |
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radius_secret_1
|
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. |
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client
|
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. |
Optional
port
|
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. Default: |
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failmode
|
Either
Default: |
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radius_ip_2
|
The IP address of your second Cisco FTD SSL VPN, if you have one. You can specify additional devices as as |
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radius_secret_2
|
The secrets shared with your second Cisco FTD SSL VPN, if using one. You can specify secrets for additional devices as |
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=safeMake sure to save your configuration file when done.
View video guides for proxy deployment at the Authentication Proxy Overview or see the Authentication Proxy Reference Guide for additional configuration options.
Open an Administrator command prompt and run:
net start DuoAuthProxyAlternatively, 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:
authproxyctl startIf the service starts successfully, Authentication Proxy service output is written to the authproxy.log file, which can be found in the log subdirectory.
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 Windows Services console or issuing these commands from an Administrator command prompt:
net stop DuoAuthProxy & net start DuoAuthProxyTo stop and restart the Authentication Proxy using authproxyctl, from an administrator command prompt run:
authproxyctl restartOpen a root shell and run:
# /opt/duoauthproxy/bin/authproxyctl startTo ensure the proxy started successfully, run:
# /opt/duoauthproxy/bin/authproxyctl statusAuthentication Proxy service output is written to the authproxy.log file, which can be found in the log subdirectory.
To stop and restart the Authentication Proxy, open a root shell and run:
# /opt/duoauthproxy/bin/authproxyctl restartIf 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 → RADIUS Server Group and click Add RADIUS Server Group.
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. |
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:
| 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. |
Once you have added the Duo RADIUS server to the group, click Save to create the new Duo RADIUS server group.
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 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: password123,123456In 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:
| 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. |
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.
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.
