CHABOT COLLEGE CISCO NETWORKING ACADEMY
Chabot College
Point-to-Point Protocol

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Point-to-Point Protocol

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Point-to-Point Protocol
• successor to SLIP
• router-to-router
• host-to-network
• synchronous or asynchronous
• developed in the 80’s

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Layering PPP Elements

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP Operation

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP Physical Interfaces
PPP runs on the following types of WAN physical interfaces:

Asynchronous serial

ISDN

Synchronous serial

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP 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.

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP Frame Example

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP Link Negotiation

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP stages
• LCP frames configure and test the data link
• The link is established, and facilities are negotiated.

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP 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.

CHABOT COLLEGE CISCO NETWORKING ACADEMY

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP LCP Configuration Options

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP LCP Configuration
Options
• PPP options:
– Authentication
– Compression
– Error Detection
– Callback
– Multilink
• Only Authentication is covered on the
CCNA exam.

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP 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.

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Compression 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.

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Compression Algorithms
• MPPC
- This protocol (RFC 2118) allows
Cisco routers to exchange compressed data with Microsoft clients. MPPC uses an LZbased compression algorithm.
• TCP header compression
- This type of compression is used to compress the TCP headers. (Good for Telnet)

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP Multilink

CHABOT COLLEGE CISCO NETWORKING ACADEMY

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PPP Authentication Overview

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Authentication Phase (optional)
Takes place before entering the networklayer protocol phase.
PPP supports two authentication protocols:
• PAP (RFC 1334)
• CHAP (RFC 1334 and 1994)

CHABOT COLLEGE CISCO NETWORKING ACADEMY
PAP
• 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

PAP
CHABOT COLLEGE CISCO NETWORKING ACADEMY

CHABOT COLLEGE CISCO NETWORKING ACADEMY
CHAP
• used at the startup of a link, and periodically
• 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

CHAP
CHABOT COLLEGE CISCO NETWORKING ACADEMY

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Configuring Authentication

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Configuring Authentication

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Verifying PPP