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:
- 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.
- 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.
- 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 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.
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
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
- 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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