Using Windows Server 2008 as a RADIUS Server for a Cisco ASA

Using Windows Server 2008 as a RADIUS Server for a Cisco ASA

Recently I needed to get a Cisco ASA 5510 to use a RADIUS Server on Server 2008 to authenticate Active Directory users for VPN access. The ASA was already configured to use a Server 2003 RADIUS server, so much of the below was just replicating the existing configuration on a 2008 server. I suspect many of the settings are less than ideal and some are unnecessary, but the below steps worked for now.

Components

·         AD1:

o    Windows Server 2008

o    Also the domain controller

o    IP: 192.168.1.10

·         CiscoASA:

o    ASA 5510 (though I believe these instructions should work for all ASA models)

o    IP: 192.168.1.2

Cisco Configuration

I performed the Cisco configuration using the ASDM management tool. The same configuration could be achieved via the command line interface, but I found the ASDM was more convenient for checking existing settings and then replicating.

Launch ASDM and connecting to the ASA, I went to the Configuration view.

Create an IP Name object for the target

1.    Under the Firewall section, expand the Objects link and select the IP Names.

2.    Click the Add button at the top.

3.    Enter a descriptive name, the IP address and a description of the server. For this server I used

4.    Name: INT-AD1

5.    IP: 192.168.1.10

6.    Description: AD / RADIUS

7.    Click OK and then Apply

Create a new AAA Server Group

1.    Click the Remote Access VPN section.

2.    Expand AAA Setup and select AAA Server Groups.

3.    Click the Add button to the right of the AAA Server Groups section.

4.    Give the server group a name, like TEST-AD, and make sure the RADIUSprotocol is selected.

5.    Accept the default for the other settings. And click OK

Add the RADIUS server to the Server Group.

1.    Select the server group created in the step above.

2.    Click the Add button to the right of Servers in the Select Group.

3.    Under the Interface Name select the interface on the ASA that will have access to the RADIUS server, most likely inside.

4.    Under Server Name or IP Address enter the IP Name you created for the RADIUS server above.

5.    Skip to the Server Secret Key field and create a complex password. Make sure you document this as it is required when configuring the RADIUS server. Re-enter the secret in the Common Password field.

6.    Leave the rest of the settings at the defaults and click Ok.

Setting Up RADIUS on Windows Server 2008

This part gave me the most trouble. The documentation from Microsoft was somewhat vague and other resources I found using the trusty Google method listed steps and addition pieces I knew to be unnecessary.

To perform the below steps you need Administrator permissions to the server that will host the RADIUS server. You also will need permissions to “Register” the server in AD. I believe this requires Domain Admin privileges.

Add the Network Policy Server function.

1.    Connect to the Windows Server 2008 server and launch Server Manager.

2.    Click the Roles object and then click the Add Roles link on the right.

3.    Click Next on the Before You Begin page.

4.    Select the Network Policy and Access Services role and click Next.

5.    Under Role Service select only the Network Policy Server service and clickNext.

6.    Click Install.

After the role finishes installing you will need to set up the server using the Network Policy Server (NPS) management tool found under Administrative Tools.

Registering the server.

1.    After launching the NPS tool right-click on the entry NPS(Local) and click theRegister Server in Active Directory.

2.    Follow the default prompts.

Create a RADIUS client entry for the ASA.

1.    Expand the RADIUS Clients and Servers folder.

2.    Right-click on RADIUS Clients and select New RADIUS Client.

3.    Create a Friendly Name for the ASA device. I used “CiscoASA” but if you had more than one you might want to make it more unique and identifiable. Make sure you document the Friendly Name used as it will be used later in some of the policies created.

4.    Enter the Server Secret Key specified on during the ASA configuration in the Shared secret and Confirm shared secret field.

5.    Leave the default values for the other settings and click OK. See Figure 1 for all the complete RADIUS Client properties.

Figure 1

Create a Connection Request Policy.

1.    Expand the Policies folder.

2.    Right-click on the Connection Request Policies and click New.

3.    Set the Policy Nameto something meaningful. I used CiscoASA because this policy is geared specifically for that RADIUS client. Leave the Type of network access server as Unspecified and click Next.

4.    Under Conditions click Add. Scroll down and select the Client Friendly Name condition and click Add…

5.    Specify the friendly name that you used when creating the RADIUS Client above. Click OK and Next.

6.    On the next two pages leave the default settings and click Next.

7.    Under the Specify a Realm Name select the Attribute option on the left. From the drop down menu next to Attribute: on the right select User-Name. Click Next again.

8.    Review the settings on the next page and click Finish.

Create a Network Policy.

1.    Right-click the Network Policy folder and click New.

2.    Set the Policy Name to something meaningful. Leave the Type of network access server as Unspecified and click Next.

3.    Under Conditions click Add.

4.    Add a UsersGroup condition to limit access to a specific AD user group. You can use a generic group like Domain Users or create a group specifically to restrict access.

5.    Add a Client Friendly Name condition and again specify the Friendly Name you used for your RADIUS client.

6.    Click Next. Leave Access granted selected and click Next again.

7.    (Important Step) On the authentication methods leave the default selection and add Unencrypted authentication (PAP, SPAP).

8.    Accept the default Constraints and click Next.

9.    Accept the default Radius Settings and click Next. Review the settings and click Finish.

Restart the Network Policy Server service.

·         This may not be necessary, but I did this at various points and cannot be certain the above steps work without restarting the service.

Test Your RADIUS Authentication

The ASDM utility includes functionality to test RADIUS Authentication.

1.    If necessary re-launch the ASDM utility.

2.    Return to Configuration -> Remote Access VPN -> AAA Setup -> AAA Server Groups.

3.    Select the new Server Group you created.

4.    From the Servers in the Selected Group section highlight the server you created. Click the Test button on the right.

5.    Select the Authentication radio button. Enter the Username and Password of a user that meets the conditions specified in the Network Policy created above then click OK.

6.    If everything works as designed you should see something similar to:

Save your Cisco Configuration

Don’t forget to save the running configuration to memory on your ASA. Otherwise you’ll lose all your settings the next time the device is rebooted.