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F5 BIG-IP APM with RADIUS and Duo Prompt

Last Updated: October 23rd, 2020

Duo integrates with your F5 BIG-IP APM to add two-factor authentication to any VPN login, complete with inline self-service enrollment and Duo Prompt.

The Duo F5 Big-IP configuration with inline enrollment and Duo Prompt supports firmware versions 11.4 and later when using Standard Customization only. The Duo Prompt is not supported in the Modern Customization type available in v15.1 and later. Ensure your BIG-IP has all current updates for your platform version.

Refer to our alternate instructions if you want to configure Duo on your BIG-IP with automatic push and phone call authentication.

Connectivity Requirements

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.

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 F5 BIG-IP APM users before you begin to deploy Duo.

To integrate Duo with your F5 BIG-IP APM, 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 F5 BIG-IP APM 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.
Treat your secret key like a password

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!

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).

  1. Download the most recent Authentication Proxy for Windows from Note that the actual filename will reflect the version e.g. duoauthproxy-5.0.2.exe. View checksums for Duo downloads here.
  2. Launch the Authentication Proxy installer on the target Windows server as a user with administrator rights and follow the on-screen prompts.
  1. 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

    On Debian-derived systems, install these dependencies by running (as root):

    $ apt-get install build-essential libffi-dev perl zlib1g-dev
  2. Download the most recent Authentication Proxy for Unix from Depending on your download method, the actual filename may reflect the version e.g. duoauthproxy-5.0.2-src.tgz. View checksums for Duo downloads here.

  3. Extract the Authentication Proxy files and build it as follows:

    $ tar xzf duoauthproxy-latest-src.tgz
    $ cd duoauthproxy-version-src
    $ make
  4. 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 you ever need to uninstall the proxy, run /opt/duoauthproxy/uninstall.

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:

Operating System Authentication
Proxy Version
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:


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. We recommend using WordPad or another text editor instead of Notepad when editing the config file on Windows.

Configure the Proxy for Duo Only Authentication

At the top of your authproxy.cfg, create a [duo_only_client] section. This section has no additional parameters to configure.


When using the [duo_only_client] configuration, the Authentication Proxy will ignore primary credentials and perform Duo factor authentication only.

Configure the Proxy for Your F5 BIG-IP APM

Next, we'll set up the Authentication Proxy to work with your F5 BIG-IP APM. Create a [radius_server_iframe] section and add the properties listed below. If you've already set up the Duo Authentication Proxy for a different RADIUS iframe application, append a number to the section header to make it unique, like [radius_server_iframe2].


type f5_bigip

Your integration key.


Your secret key.


Your API hostname (e.g. "").


The IP address of your F5 BIG-IP APM.


A secret to be shared between the proxy and your F5 BIG-IP APM. 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.


Use Active Directory for primary authentication. Make sure you have an [ad_client] section configured.


Use RADIUS for primary authentication. Make sure you have a [radius_client] section configured.


Do not perform primary authentication. Make sure you have a [duo_only_client] section configured.

This parameter is optional if you only have one "client" section. If you have multiple, each "server" section should specify which "client" to use.



The 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: 1812.


Either "safe" or "secure":


In the event that Duo's service cannot be contacted, users' authentication attempts will be permitted if primary authentication succeeds. This is the default.


In the event that Duo's service cannot be contacted, all users' authentication attempts will be rejected.


The IP address of your second F5 BIG-IP APM, if you have one. You can specify additional devices as as radius_ip_3, radius_ip_4, etc.


The secrets shared with your second F5 BIG-IP APM, if using one. You can specify secrets for additional devices as radius_secret_3, radius_secret_4, etc. If you're on Windows and would like to encrypt this secret, see Encrypting Passwords in the full Authentication Proxy documentation.

A completed config file, with the Authentication Proxy only performing secondary authentication, should look something like:


Make 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.

Start the Proxy

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.

If 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 DuoAuthProxy

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 log subdirectory.

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.

Configure Your F5 BIG-IP APM

  1. Log into the BIG-IP management console and navigate to Access PolicyAAA ServersRADIUS and click the Create button.

    Enter a name for your new Duo RADIUS server. Set the Mode to "Authentication" and fill in the host/port/secret information that corresponds to your Duo Authentication Proxy configuration. Be sure to increase the timeout to 60 seconds and set the character set to utf-8.

    Duo RADIUS AAA Server

  2. You'll need to modify an existing Access Policy to use the newly defined Duo RADIUS server for authentication (or create a new one). Navigate to Access PolicyAccess ProfilesAccess Profiles List and click the Edit... link in the Access Policy column of the profile you want to update to use Duo.

    Use the Access Policy editor to insert the Duo RADIUS authentication method after success with your current authentication method (like AD/LDAP). Click the plus symbol in the "Successful" arrow coming off your primary authenticator and type "RADIUS" in the search field on the subsequent page. Select RADIUS Auth and click Add Item.

    On the RADIUS Auth properties tab select your Duo RADIUS system in the AAA Server drop-down and cick Save.

    Your policy now shows two authenticators (your original method followed by RADIUS).

    In this example, Duo RADIUS authentication has been added to an existing Access Policy after successful primary AD authentication.

    Adding Duo to an Access Policy

    Click Close to exit the Access Policy editor and return to the Access Profile List page. The profile you just modified may have a yellow status flag. Click the checkbox next to that policy to select it and then click Apply Access Policy. The status flag will turn green.

    Consult the BIG-IP Access Policy Manager Configuration Guide for more information about creating and modifying Access Policies or contact F5 support.

  3. Navigate to Access PolicyCustomizationAdvanced and change the "Edit Mode" to Advanced. Navigate through the Access Profiles tree to the Common folder beneath your Access Policy.

  4. Add the Duo script, using the instructions for your BIG-IP firmware version:

    Click on the item and then insert the following JS snippet at the end of the Advanced Customization Editor Footer text input box and click Save:

    <script src=""></script>

    Editing the header

    Click on the item and then insert the following JS snippet at the end of the Advanced Customization Editor Footer text input box and click Save:

    <script src=""></script>

    Editing the footer

  5. While still in Access Policy Advanced Customization Editor, navigate through the Access Profiles tree to Access Policy > Logon Pages > Logon Page folder beneath your Access Policy.

    Click the item and locate the <head> section of the page in the Advanced Customization Editor (around line 90):

    Add this line to the <head> section after the first meta http-equiv line and click Save:

    <meta http-equiv="X-UA-Compatible" content="IE=Edge" />

    Editing the logon page

Save the customization changes and return to the Access Profile List page. The profile you just modified may have a yellow status flag. Click the checkbox next to that policy to select it and then click Apply Access Policy. The status flag will turn green.

Test Your Setup

To test your setup, go to the URL you normally use to log in to your F5 BIG-IP APM in a browser window. After you complete primary authentication, the Duo Prompt or enrollment page appears.

BIG-IP APM SSL VPM Login with Duo Prompt

Enable Hostname Whitelisting

If you plan to permit use of WebAuthn authentication methods (security keys, U2F tokens, or Touch ID), Duo recommends enabling hostname whitelisting for this application and any others that show the inline Duo Prompt before onboarding your end-users.

The BIG-IP Edge Client also supports authentication with the Duo Prompt.

BIG-IP APM Edge Client Login with Duo Prompt


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 F5 BIG-IP Frequently Asked Questions (FAQ) page or try searching our F5 BIG-IP Knowledge Base articles or Community discussions. For further assistance, contact Support.

Network Diagram

  1. Primary authentication initiated to F5 BIG-IP APM
  2. F5 BIG-IP APM verifies primary logon credentials with external directory using Active Directory or RADIUS
  3. F5 BIG-IP APN sends authentication request to Duo Security’s authentication proxy
  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. F5 BIG-IP APM access granted