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Documentation

Barracuda SSL VPN - Alternate Configuration

Last Updated: September 11th, 2019

Duo integrates with your Barracuda SSL VPN to add two-factor authentication to any VPN login, complete with inline self-service enrollment and Duo Prompt.

Overview

To integrate Duo with your Barracuda 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 additional RADIUS server to use Duo.

Once configured, Duo sends your users an automatic authentication request via Duo Push notification to a mobile device or phone call after successful primary login.

This configuration doesn't support inline self-service enrollment. You'll need to create your users in Duo ahead of time using one of our other enrollment methods, like directory sync or CSV import. Read the enrollment documentation to learn more.

If you are using only browser based logons with Barracuda's SSL VPN, please follow our SSL VPN instructions to add two-factor authentication to browser VPN login, complete with inline self-service enrollment and Duo Prompt.

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 Barracuda SSL VPN users before you begin to deploy 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 2008 R2 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 Barracuda SSL VPN in the applications list. Click Protect this Application to get your integration key, secret key, and API hostname. See Getting Started for help.
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 https://dl.duosecurity.com/duoauthproxy-latest.exe. Note that the actual filename will reflect the version e.g. duoauthproxy-3.1.1.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, Python 2.6 or 2.7 (including development headers and libraries), 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 python-devel libffi-devel perl zlib-devel

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

    $ apt-get install build-essential python-dev libffi-dev perl zlib1g-dev
  2. Download 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-3.1.1-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:

Platform Default Configuration Path
Windows (64-bit) C:\Program Files (x86)\Duo Security Authentication Proxy\conf\authproxy.cfg
Windows (32-bit) C:\Program Files\Duo Security Authentication Proxy\conf\authproxy.cfg
Linux /opt/duoauthproxy/conf/authproxy.cfg

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

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 service_account_username. If you're on Windows and would like to encrypt this password, see Encrypting Passwords in the full Authentication Proxy documentation.

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:

search_dn=DC=example,DC=com

Optional

host_2

The hostname or IP address of a secondary/fallback domain controller. You can add additional domain controllers as host_3, host_4, etc.

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. Other users will not pass primary authentication. For example:

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

host

The IP address of your RADIUS server. You can add backup servers with host_2, host_3, etc.

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 port_2, port_3, etc. to specify ports for the backup servers.

Default:1812

pass_through_all

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.

Default: false

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 Barracuda SSL VPN

Next, we'll set up the Authentication Proxy to work with your Barracuda SSL VPN. Create a [radius_server_auto] section with the following properties:

Required

ikey

Your Duo integration key, obtained from the details page for the application in the Duo Admin Panel.

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.

api_host

Your Duo API hostname (e.g. api-XXXXXXXX.duosecurity.com), obtained from the details page for the application in the Duo Admin Panel.

radius_ip_1

The IP address of your Barracuda SSL VPN. Only clients with configured addresses and shared secrets will be allowed to send requests to the Authentication Proxy.

radius_secret_1

A secret to be shared between the proxy and your Barracuda SSL VPN. If you're on Windows and would like to encrypt this secret, see Encrypting Passwords in the full Authentication Proxy documentation.

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.

ad_client

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

radius_client

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

duo_only_client

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.

Optional

port

Port on which to listen for incoming RADIUS Access Requests.

Default: 1812

failmode

Either safe or secure:

Failmode

Description

safe

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

secure

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

Default: safe

radius_ip_2

The IP address of your second Barracuda SSL VPN, if you have one. You can specify additional devices as as radius_ip_3, radius_ip_4, etc.

radius_secret_2

The secrets shared with your second Barracuda SSL VPN, 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 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

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.

Note

View video guides for proxy deployment at the Authentication Proxy Overview or see the Authentication Proxy Reference Guide for additional configuration options.

Configure Your Barracuda SSL VPN

Add an Authentication Scheme

  1. Log in to the Barracuda administrative interface.
  2. Navigate to Access Control → Authentication Schemes in the administrative interface.
  3. Add a new authentication scheme with the following information:

    Name Duo RADIUS
    Selected modules Add the "RADIUS" module from the "Available modules" box
    Selected policies Add the desired policies from the "Available policies" box
  4. Click the Add button to create the authentication scheme.

Configure the RADIUS Settings

  1. Navigate to Access Control → Configuration in the administrative interface.
  2. In the RADIUS section, modify the following settings:

    RADIUS server The IP address of your Duo Authentication Proxy
    Shared secret The RADIUS secret shared with your Duo Authentication Proxy
    Authentication method PAP
    Password prompt text Password
    Reject challenge No
  3. Click the Save Changes button to save the RADIUS settings.

Test Your Setup

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:

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.

Troubleshooting

Need some help? Take a look at our Barracuda Knowledge Base articles or Community discussions. For further assistance, contact Support.