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Cisco Firepower Threat Defense (FTD) VPN with AnyConnect

Last Updated: April 15th, 2019

Duo integrates with your Cisco Firepower Threat Defense (FTD) SSL VPN to add tokenless two-factor authentication to AnyConnect VPN logins.

Overview

Duo MFA for Cisco Firepower Threat Defense (FTD) supports push, phone call, or passcode authentication for AnyConnect desktop, AnyConnect mobile client, or browser VPN connections that use SSL encryption. This configuration does not feature the interactive Duo Prompt for web-based logins, but does capture client IP informations 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.

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.

Walkthrough Video

First Steps

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.

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 7 or later, CentOS 7 or later, or 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 Cisco Firepower Threat Defense 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-3.0.0.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-3.0.0-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 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 Cisco FTD SSL VPN

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

Required

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 Cisco FTD SSL VPN.
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.
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 Cisco FTD 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 Cisco FTD 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.

Note

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 Cisco FTD using FMC

Add the Duo RADIUS server

  1. Log into the FMC console that manages your FTD SSL VPN devices.

  2. Navigate to ObjectsObject ManagementRADIUS Server Group and click Add RADIUS Server Group.

  3. 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.
  4. In the "RADIUS Servers" section of the form, click the green plus sign to add a RADIUS server.

  5. 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.

    FMC Completed New RADIUS Server Form

  6. Once you have added the Duo RADIUS server to the group, click Save to create the new Duo RADIUS server group.

    FMC Completed Add RADIUS Server Group Form

Change the Remote Access VPN Authentication Method to Duo RADIUS

  1. Navigate to DevicesVPNRemote Access.
  2. Click on the VPN configuration to which you want to add Duo.
  3. 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.
  4. Once on the "Edit Connection Profile" form, click the AAA tab.
  5. Change the "Authentication Server" from the existing selection to the Duo RADIUS server group you created earlier.
  6. You typically do not need to select an "Authorization Server" or "Accounting Server".
  7. Do not configure the "Password Management" options.
  8. Click the Save button on the "Edit Connection Profile" form

    FMC Update VPN Connection Profile for Duo RADIUS

  9. Click the Save button in the upper right of the FMC console window (where it says "You have unsaved changes").

Deploy Changes to FTD devices

  1. Click the Deploy button in the top right of the FMC site.
  2. Select the FTD device (or devices) to which you want to push the new Remote Access VPN config with Duo.
  3. Click the Deploy button.
  4. Watch for the deployment to complete with the status "Deployment to device successful".

Test Your Setup

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: password123,123456

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 activate 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.

AnyConnect Client with Duo RADIUS

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.

Troubleshooting

Need some help? 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.

Network Diagram

  1. Primary authentication initiated to Cisco FTD
  2. Cisco FTD sends authentication request to the Duo Authentication Proxy
  3. Primary authentication using Active Directory or RADIUS
  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. Cisco FTD VPN access granted

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