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Setting Up Server 2003 as a RADIUS with DD-WRT

A co-worker of mine was having some difficulties in setting up a RADIUS for his wireless network which is what prompted this particular article. For setting up your wireless infrastructure there are times when you need a more centrally controlled solution for the authentication problem. This is where RADIUS, and more to the point Microsoft’s IAS, steps in. For your trivia needs RADIUS stands for Remote Authentication Dial-In User Service, while IAS stands for Internet Authentication Service. Normally I would be setting this up under Server 2008 but our needs were calling for Server 2003. I may follow-up with how to do this under Server 2008 as well and even delve into putting together an IAS farm. The WAP being used is a Buffalo WHR-125 with a fairly current build of DD-wrt v24 SP2 (09/24/09) on it.

First off before installing IAS we will be in need of a certificate for it to use. There are several ways of achieving this. The first method, and easiest/cheapest, is creating a self-signed certificate using the IIS 6 Resource Kit from Microsoft. A particular program need from this is SelfSSL so run through a custom installation and install SelfSSL. Open up a command prompt and navigate to where SelfSSL installed at and here is how we will be constructing a certificate:

C:\Program Files\IIS Resources\SelfSSL>selfssl  /N:CN=server.domain.local /K:1024 /V:1825

This will get you your self-signed certificate. Of course you can use 3rd party certificates as well. Another method is to issue one from an internal CA. Don’t forget to implement CA best practices when using one. I personally would opt for a self-signed certificate unless you already have a CA available.

Next up is getting our IAS installed. You will find this from Add/Remove Programs Add/Remove Windows Components. In there look for Networking Services and go into Details. Internet Authentication Service will be displayed just a few down. Once installed open up the mmc for IAS and let’s get into configuration. Though we should set up our users first. I went with creating a security group named Wireless Authentication and added my users in there. Note that you will need to allow these users for remote access as well. One way is to go into the user’s properties and on the Dial-In tab select Allow access. This isn’t my preferred method though as it creates more work. The other method I shall detail a bit later.

Bring up your IAS controls and you’ll see categories available. We need to get ourselves configured for our access point. To do this we will create a RADIUS Client. Right click on RADIUS Clients and select New RADIUS Client. Give the policy a name and point it to the address of the access point. Next menu is selecting our vendor which we will want to keep as RADIUS Standard for our configuration, as well as most configurations.  Put in a key for this client and note it down as we will need to configure it in the WAP later on. No need for the Message Authenticator attribute as it is used by default with EAP, which is what we will be configuring. For more information about it read here.

We have our client configured on the server but we are also in need of a Remote Access Policy. Right click the Remote Access Policies and select New Remote Access Policy. We will go with the first option for setting up our policy, though creating a custom policy is easy enough as well. On the next screen Access Method we will select Wireless. On the next screen we can put our group to use. Add in your Wireless Authentication group, unless you prefer to control things at the user level. I prefer security groups so that is what we will use. Select PEAP for the authentication method. Check the configuration of it to ensure that EAP-MSCHAP V2 is selected and that the proper certificate is selected as well. If you get an error when selecting Configure complaining about certificates then you need to go back and verify that you have a properly issued certificate. This is where most problems stem from. In the configuration you may also wish to enable Fast Reconnect. I have read about some clients having issues with this but have not had any problems in my configuration. Your mileage may vary. Disable it if you are having problems authenticating clients routinely. Finish this wizard and you’ll have your policy. We’re not quite done with it yet though.

Bring up the properties on your newly created policy. On the encryption tab you will want only Strongest encryption checked. If there are authentication issues though, you will want to enable the others for diagnostics until you figure out what is properly supported by your WAP. This is also where we can enable the alternate method for allowing our users. Go to the Advanced tab and add Ignore-User-Dialin-Properties set to True. This will ignore the setting on your user’s Dial-in tab and truly allow you to control access via groups. Otherwise user settings will trump group settings, which can make for a headache in troubleshooting. Last thing to do is right click the root folder, Internet Authentication Service, and select Register server in Active Directory. What this does is add your server to the RAS and IAS Servers security group, which enables it to read accounts from your AD. Once we are done here we can finally go configure our access point.

This is specific to DD-WRT, so be sure to verify how to configure your own access point. Connect to your access point and go to the Wireless tab, then Wireless Security. Set it to WPA2 Enterprise and make sure you are using AES, unless you have a reason not to. Put in the address for your IAS server and now would be a great time to make sure that it is a static address. Leave the port as 1812 as IAS listens on that out of the box. Finally put in the preshared key that you configured from earlier. Save then apply and your access point is in business. All that is left is configuring your clients.

This is best done through Windows’ wireless configuration. Manually create a new connection configured with your WAP’s SSID and go into the Security settings on it. Set it to use PEAP and if you are using a non-domain joined machine, that also does not have the certificate that you configured the server with, then tell it not to validate the certificate and also not to use your domain logon and password. Connect wirelessly to your access point and see if you’re successful. If you are not then check your server’s System event log for errors. If you are getting bad username/password errors, and you know your username and password are correct, then start looking at your encryption and configured authentication protocols to make sure they all match. If you are seeing errors about no matching policy then make sure you have your user in the right group or matching the criteria of your policy. That covers the majority of problems you will run into when configuring IAS. Even if you don’t have a use for IAS as a RADIUS it is a good idea to set it up a few times for learning purposes when pursuing an MCSE.
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