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Barracuda SSL VPN

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.

If you are using the Barracuda VPN Client then see the Alternate VPN Client Instructions to configure the Barracuda device to use Duo Security's automatic push authentication.

First Steps

To integrate Duo with your Barracuda SSL VPN, you will need to install a local proxy service on a machine within your network. Before proceeding, you should locate (or set up) a system on which you will install the Duo Authentication Proxy. The proxy supports Windows and Linux systems (in particular, we recommend Windows Server 2012 R2 or later, Red Hat Enterprise Linux 6 or later, CentOS 6 or later, or Debian 6 or later).

This Duo proxy server also acts as a RADIUS server — there's no need to deploy a separate RADIUS server to use Duo.

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.
Connectivity Requirements

This integration communicates with Duo's service on TCP port 443. Also, we do not recommend locking down your firewall to individual IP addresses, since these may change over time to maintain our service's high availability.

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-2.6.0.exe.
  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 OpenSSL, 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 openssl-devel python-devel libffi-devel

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

    $ apt-get install build-essential libssl-dev python-dev libffi-dev

    To ensure that your Python version will work with the Authentication Proxy, run:

    $ python --version

    If the output does not say "Python 2.6.x" or "Python 2.7.x", first take note that many distributions can support multiple versions of python simultaneously. If your python installation does not appear to be a supported version, try replacing "python" in the above command with "python2.6" or "python2.7". If neither of these work, then you will need to install a different version of Python. You may need to search additional repositories for your distribution (e.g. for Centos or Red Hat Enterprise Linux, Extra Packages for Enterprise Linux), or build Python from source.

  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-2.6.0-src.tgz.

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

    $ tar xzf duoauthproxy-latest-src.tgz
    $ cd duoauthproxy-version-src
    $ export PYTHON=python_command
    $ make
    Where python_command is the command to run a Python 2.6 or Python 2.7 interpreter (e.g. "python", "python2.6", "python2.7").
  4. Install the authentication proxy (as root):

    $ cd duoauthproxy-build
    $ ./install

    Follow the prompts to complete the installation.

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 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 member account that has permission to bind to your Active 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. By default, the proxy will attempt to contact your RADIUS server on port 1812. Use port_2, port_3, etc. to specify ports for the backup servers.
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_iframe] section with the following properties:

Required

type barracuda
ikey Your integration key.
skey Your secret key.
api_host Your API hostname (e.g. "api-XXXXXXXX.duosecurity.com").
radius_ip_1 The IP address of your Barracuda SSL VPN.
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 The port on which to listen for incoming RADIUS Access Requests. Default: 1812.
failmode

Either "safe" or "secure":

"safe" In the event that Duo's service cannot be contacted, users' authentication attempts will be permitted if primary authentication succeeds. This is the default.
"secure" In the event that Duo's service cannot be contacted, all users' authentication attempts will be rejected.
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, using Active Directory as the primary authenticator, 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_iframe]
type=barracuda
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

Alternatvely, 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, go to the URL you normally use to log in to your Barracuda SSL VPN. After you complete the primary authentication, Duo enrollment/login should appear.

Troubleshooting

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

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