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Point-to-Point ProtocolPoint-to-Point Protocol

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Point-to-Point ProtocolPoint-to-Point Protocol

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Point-to-Point ProtocolPoint-to-Point Protocol

• successor to SLIP

• router-to-router

• host-to-network

• synchronous or asynchronous

• developed in the 80’s

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Layering PPP ElementsLayering PPP Elements

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PPP OperationPPP Operation

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PPP Physical InterfacesPPP Physical Interfaces

PPP runs on the following types of WAN physical interfaces:

Asynchronous serial ISDN Synchronous serial

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PPP Datagram TransmissionPPP Datagram Transmission

Encapsulation - supports HDLC protocol to provide encapsulation.

Link Control Protocol (LCP) - used to establish, configure, and test the data link.

Network Control Protocols (NCPs) - used to establish and configure different network layer protocols.

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PPP Frame ExamplePPP Frame Example

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PPP Link NegotiationPPP Link Negotiation

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PPP stagesPPP stages

• LCP frames configure and test the data link

• The link is established, and facilities are negotiated.

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PPP stagesPPP stages

• NCP frames are sent to choose and configure network layer protocols.

• The chosen network layer protocols (IP, IPX, etc.) are configured, and packets from each network layer protocol are sent.

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LCP Options

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PPP LCP Configuration OptionsPPP LCP Configuration Options

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PPP LCP Configuration PPP LCP Configuration OptionsOptions• PPP options:

– Authentication– Compression– Error Detection– Callback– Multilink

• Only Authentication is covered on the CCNA exam.

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PPP CompressionPPP Compression

• Compression should only be used on low speed WAN interfaces (typically 56 Kbps and less).

• When compression is performed in software, it might substantially degrade system performance. – Disable compression if the router CPU load

exceeds 40 percent.

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Compression AlgorithmsCompression Algorithms

• Predictor - Determines whether the data is already compressed. If so, the data is just sent-no time is wasted trying to compress already compressed data.

• Stacker - A Lempel-Ziv (LZ)-based compression algorithm looks at the data, and sends each data type only once with information about where the type occurs within the data stream. The receiving side uses this information to reassemble the data stream.

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Compression AlgorithmsCompression Algorithms

• MPPC - This protocol (RFC 2118) allows Cisco routers to exchange compressed data with Microsoft clients. MPPC uses an LZ-based compression algorithm.

• TCP header compression - This type of compression is used to compress the TCP headers. (Good for Telnet)

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PPP MultilinkPPP Multilink

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PPP Authentication

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PPP Authentication OverviewPPP Authentication Overview

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Authentication Phase (optional)Authentication Phase (optional)

Takes place before entering the network-layer protocol phase.

PPP supports two authentication protocols:

• PAP (RFC 1334)

• CHAP (RFC 1334 and 1994)

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PAPPAP• simple

• two-way handshake

• done only upon initial link establishment

• passwords are sent across the link in cleartext

• remote node is in control of the frequency and timing of the login attempts

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PAPPAP

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CHAPCHAP

• used at the startup of a link, and periodicallyperiodically

• three-way handshake

• the local router sends a “challenge” message to the remote node

• local router (or a third-party authentication server such as TACACS) is in control of the frequency and timing of the challenges

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CHAPCHAP

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Configuring AuthenticationConfiguring Authentication

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Configuring AuthenticationConfiguring Authentication

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Verifying PPPVerifying PPP