Accept Incoming Connections Using PAP

use /allow switch (multiple choice: mschap2, mschap1, chap, pap; default: mschap2, mschap1, chap, pap) - the protocol to allow the client to use for authentication

I don't understand what you mean. Can you explain to me more clearly? Is there any "/allow" in windows xp?

Windows XP PPPoE connections support PAP authentication and, by default, the PPPoE connection allows the use of unsecured passwords. Windows XP PPPoE connection will attempt to use secured password authentication protocols such as Microsoft Challenge Handshake Authentication Protocol version 2 (MS-CHAP v2), Microsoft Challenge Handshake Authentication Protocol (MS-CHAP), Challenge Handshake Authentication Protocol (CHAP), and Shiva Password Authentication Protocol (SPAP), before offering to use PAP.

Microsoft recommends that you use MS-CHAP v2, MS-CHAP, or CHAP for your authentication protocol. If your ISP supports one of these secured password authentication protocols and you want to ensure that PAP and SPAP are used, deselect "Require secured password" under Validate my identity as follows using typical security settings on the Security tab from the properties of the PPPoE connection

http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/pppoe.mspx
http://www.mikrotik.com/docs/ros/2.8/interface/pppoe
http://www.carricksolutions.com/raspppoe.php
http://www.expita.com/earthlink.html

Hope that helps,

Engineer_Dell

Thanks for reply. For some reason, I just wanna force my newly created PPPoE server on Windows XP to use only PAP authentication, and I don't wanna configure any thing on the client side. Or is there any PPPoE Server supporting PAP that will run on Windows? Thanks in advance.