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PPP Protocol Overview

The Point-to-Point Protocol (PPP), documented in RFC 1661, is currently (early 1996) the best solution for dial-up Internet connections, including ISDN.

PPP is a layered protocol, starting with a Link Control Protocol (LCP) for link establishment, configuration and testing. Once the LCP is initialized, one or many of several Network Control Protocols (NCPs) can be used to transport traffic for a particular protocol suite. The IP Control Protocol (IPCP), documented in RFC 1332, permits the transport of IP packets over a PPP link. Other NCPs exist for Appletalk (RFC 1378), OSI (RFC 1377), DECnet Phase IV (RFC 1762), Vines (RFC 1763), XNS (RFC 1764) and transparent Ethernet bridging (RFC 1638).

Here are some key PPP features, all of which are lacking in SLIP:

• Address Notification allows a server to inform a dial-up client of its IP address for that link, but the mechanism is powerful enough for clients to request IP addresses and supports fallback configurations. SLIP required the user to configure this information manually. PPP options have also been specified (RFC 1877) for notification of name server addresses, both Internet and NetBios.

• Authentication is available as an option, either with the Password Authentication Protocol (PAP), or the Challenge-Handshake Authentication Protocol (CHAP). Both are documented in RFC 1334.

• Multiple Protocols can interoperate on the same link, simply by running additional NCPs. For example, both IP and IPX traffic can share a PPP link.

• Link Monitoring facilities include a link-level echo facility which can periodically check link operation.