This article defines Point-to-Point Protocol (PPP) and discusses the dial-up sequence that the Windows Remote Access Service (RAS) implements.
The Point-to-Point Protocol is a set of industry-standard protocols that
enable remote access solutions to interoperate in a multivendor network.
PPP support in Windows XP ensures that Windows XP-based workstations
can dial to remote networks through any industry-standard PPP remote
access server. PPP also enables Windows XP to receive calls from,
and provide network access to, other vendors' remote access workstation
PPP support for IPX/SPX and TCP/IP makes Windows XP "Internet-ready" and makes Windows XP an ideal operating system for mobile computing over a network, whether the network comprises a small workgroup or a large enterprise.
PPP Dial-Up Sequence
In the PPP dial-up sequence, PPP must:
- Negotiate link control protocols (LCPs).
LCPs establish and configure link and framing parameters, for example, maximum frame size. For additional information, refer to the "PPP Framing" section of this article.
- Negotiate authentication protocols.
Authentication protocols determine what level of security validation the remote access server can perform and what level the server requires. The level of security that can be negotiated ranges from clear-text password authentication to encrypted authentication to callback security. For more information about each type of authentication protocol, refer to the "Authentication Protocols" section of this article.
- Negotiate network control protocols (NCPs).
NCPs establish and configure parameters for different network protocols, such as Internet Protocol (IP), Internetwork Packet eXchange (IPX), and NetBIOS Frame Protocol (NBF). Negotiation includes negotiating protocol header compression and compression control protocol. For more information about each type of NCP, refer to the "Network Control Protocols" section of this article.
The connection that is established by the negotiations remains active
until the line is disconnected for any of the following reasons:
- The user explicitly hangs up the line.
- The line drops the connection because of a timeout for idle time.
- An administrator hangs up the line.
- An unrecoverable link error occurs.
PPP framing defines how data is encapsulated before transmission on the
wide area network (WAN). By providing a standard framing format, PPP
ensures that various vendors' remote access solutions can communicate and can recognize data packets that come from each other. PPP uses High-Level Data Link Control (HDLC) framing for serial, Integrated Services Digital Network (ISDN), and X.25 data transfers.
Negotiation of authentication protocols occurs immediately after link
quality determination and before network layer negotiation. The two most
common types of authentication protocols are:
- Password Authentication Protocol (PAP), which uses clear-text passwords and is the least sophisticated authentication protocol. PAP is typically negotiated if the remote workstation and server cannot negotiate a more secure form of validation. The Windows RAS server has an option that prevents negotiation of clear-text passwords, enabling system administrators to enforce a high level of security.
- Challenge-Handshake Authentication Protocol (CHAP), which uses challenge\response authentication with one-way encryption on the response.
Windows-based systems always negotiate encrypted authentication when they are communicating with each other. When the connection is to third-party remote access servers or client software, RAS may negotiate clear-text
authentication if the third-party product does not support encrypted
Network Control Protocols
The three most common types of NCPs are:
- Internet Protocol Control Protocol (IPCP), which can configure and enable or disable IP protocol modules at both ends of the link.
- Internet Packet eXchange Control Protocol (IPXCP), which can configure and enable or disable IPX protocol modules on both ends of the link. IPXCP is widely implemented by PPP vendors. IPX-WAN protocol is Novell's alternative to IPXCP. IPX-WAN is not compatible with IPXCP. Eventually, IPX-WAN and IPXCP might converge to provide one standard for IPX network configuration over wide area networks. Windows provides support for IPXCP, which is implemented by the vast majority of vendors of products for remote access.
- NetBIOS Frames Control Protocol (NBF CP), which can configure and enable or disable NetBEUI protocol modules on both ends of the link. Microsoft has proposed NBF CP as a protocol for NetBEUI configuration. NBF CP is in "draft" status with the Internet Engineering Task Force (IETF).
The third-party products that are discussed in this article are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.