PPP Dial-Up Sequence

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This article defines Point-to-Point Protocol (PPP) and discusses its Dial Up sequence implemented with the Windows Remote Access Service (RAS).


What is PPP?

The Point-to-Point Protocol is a set of industry standard protocols that enable remote access solutions to interoperate in a multi-vendor network. PPP support in Windows ensures that Windows workstations can dial up to remote networks through any industry standard PPP remote access server. It also enables Windows to receive calls from, and provide network access to other vendors' remote access workstation software. PPP support for TCP/IP, IPX, and NetBEUI makes Windows an "Internet-ready" and ideal mobile computing operating system for networks ranging from small workgroups to large enterprises.

PPP Dial-Up Sequence

The dial up sequence for PPP involve the following:
  1. Negotiate Link Control Protocols (LCP). LCP is used to establish and configure link and framing parameters such as maximum frame size. For additional information, refer to the PPP Framing section below.
  2. Negotiate Authentication Protocols. Authentication protocols are used to determine what level security validation the remote access server can perform, and what 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 on each type of authentication protocol, refer to the Authentication Protocols section below.
  3. Negotiate Network Control Protocols (NCP). NCPs are used to establish and configure different network protocol parameters, such as IP, IPX and NBF. This includes negotiating protocol header compression and compression control protocol. For more information on each type of NCPs, refer to the Network Control Protocols section below.
After the above negotiations, the resulting connection remains active until the line is disconnected due to any of the following reasons:

  • User explicitly hangs up the line
  • Line drops due to idle time-out
  • Administrator hangs up the line or
  • An unrecoverable link error occurs

PPP Framing

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 recognize data packets from each other. PPP uses HDLC framing for serial, ISDN and X.25 data transfers.

Authentication Protocols

Negotiation of authentication protocols occurs immediately after link quality determination and before network layer negotiation. The two most common types of authentication protocols are as follows:
  • Password Authentication Protocol (PAP) uses clear text passwords and is the least sophisticated authentication protocol. It 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 clear text passwords from being negotiated. This enables system administrators to enforce a high level of security.
  • Challenge-Handshake Authentication Protocol (CHAP) uses a challenge response with a one way encryption on the response.
Windows always negotiates encrypted authentication when communicating with each other. When connecting to third-party remote access servers or client software, RAS may negotiate clear text authentication if the third-party product does not support encrypted authentication.

Network Control Protocols

The three most common types of Network Control protocols are as follows:

  • Internet Protocol Control Protocol (IPCP) is used for configuring, enabling, and disabling IP Protocol modules at both ends of the link.
  • Internet Packet eXchange Control Protocol (IPXCP) is used for configuring, enabling and disabling 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. Over time, IPX-WAN and IPXCP may converge to provide one standard for IPX network configuration over wide area network. Windows provides support for IPXCP which is implemented by the vast majority of remote access vendors today. Windows NT 3.5 does not yet support IPX-WAN.
  • NetBIOS Frames Control Protocol (NBF CP) is used for configuring, enabling and disabling NetBEUI protocol modules on both ends of the link. NBF CP is a Microsoft proposed protocol for NetBEUI configuration. NBF CP is in "draft" status with the Internet Engineering Task Force(IETF).

The Microsoft NBF extension for PPP is documented at:
This document is a proposed RFC for the NBF control protocol. The third-party products discussed here are manufactured by vendors independent of Microsoft; we make no warranty, implied or otherwise, regarding these products' performance or reliability.


Article ID: 124036 - Last Review: February 20, 2007 - Revision: 2.2
  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Professional Edition
  • Microsoft Windows 2000 Datacenter Server
  • Microsoft Windows NT Server 3.5
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 4.0 Developer Edition
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