How to Force Routing and Remote Access to Use PAP

This article discusses the method for forcing a Routing and Remote Access (RRAS) server for Windows NT 4.0 to authenticate RAS clients using PAP instead of CHAP, SPAP, or MS-CHAP. This may be necessary, depending on your RAS clients or some third-party authentication solutions.

If your RRAS server is configured to "Allow any authentication including clear text," a RAS client is able to connect with PAP, SPAP, CHAP, or MS- CHAP depending, on what the client supports. Normally, a Microsoft RAS client will attempt to connect with CHAP or MS-CHAP, if that is valid for the RAS server to which it is connecting.

To force a RAS client to use PAP, you must delete the SPAP and CHAP registry keys from your RAS Server using the following steps:

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

1. Start Registry Editor (Regedt32.exe).
2. Go to the following subkey:
   

         HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\PPP
   						

3. Click SPAP, click Edit, and click Delete.
4. Click Yes to confirm the deletion.
5. Click CHAP, click Edit, and click Delete.
6. Click Yes to confirm the deletion.
7. Close Registry Editor and stop and restart the Routing and Remote Access Service.

NOTE: This will not work on normal Windows NT RAS servers, only Windows NT 4.0 RAS servers that have Routing and Remote Access installed. If you delete these registry keys on a normal RAS server, the RAS services will fail to start after you restart.

The following two scenarios require the above steps to force RAS clients to use PAP authentication:

• You are using a PPP client that can only use PAP, but does not notify the RAS server that it needs to use PAP during the LCP negotiation.
  
  -or-
  
  
• You are using the new Radius client included in the Routing and Remote Access Service Update. Many Radius servers do not accept the attribute 60 CHAP Challenge that the Radius Client sends to the Radius server when authenticating a RAS client using CHAP. This is a valid attribute according to RFC 2058: "Remote Authentication Dial In User Service (RADIUS)"; however, many older Radius servers cannot handle this newer attribute.

For additional information, please see the following article(s) in the Microsoft Knowledge Base: