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CCNA Guide to Cisco Networking Fundamentals Fourth Edition. Chapter 11 PPP and Frame Relay. Objectives. Describe PPP encapsulation Configure PPP encapsulation and its options Describe and enable PPP multilink Understand Frame Relay standards and equipment. Objectives (continued).

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Ccna guide to cisco networking fundamentals fourth edition

CCNA Guide to Cisco Networking Fundamentals Fourth Edition

Chapter 11

PPP and Frame Relay


Objectives
Objectives

  • Describe PPP encapsulation

  • Configure PPP encapsulation and its options

  • Describe and enable PPP multilink

  • Understand Frame Relay standards and equipment

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Objectives continued
Objectives (continued)

  • Describe the role of virtual circuits and performance parameters in Frame Relay

  • Understand the Frame Relay topologies

  • Understand the difference between multipoint and point-to-point configurations

  • Configure and monitor Frame Relay

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


PPP

  • PPP

    • Internet standard protocol defined in RFCs 2153 and 1661

    • Provide point-to-point, router-to-router, host-to-router, and host-to-host connections

    • Considered a peer technology based on its point-to-point physical configuration

    • Commonly used over dial-up or leased lines to provide connections into IP networks

  • Serial Line Internet Protocol (SLIP) was the predecessor to PPP

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Ppp continued
PPP (continued)

  • PPP can be used over several different physical interfaces, including the following:

    • Asynchronous serial

    • ISDN synchronous serial

    • High-Speed Serial Interface (HSSI)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Ppp in the protocol stack
PPP in the Protocol Stack

  • You can use PPP over both asynchronous and synchronous connections

    • At the Physical layer of the OSI reference model

  • Link Control Protocol (LCP)

    • Used at the Data Link layer to establish, configure, and test the connection

  • Network Control Protocols (NCPs)

    • Allow the simultaneous use of multiple Network layer protocols and are required for each protocol that uses PPP

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Ppp in the protocol stack continued
PPP in the Protocol Stack (continued)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame format
Frame Format

  • PPP is based on the High-Level Data Link Control (HDLC) protocol

  • The difference between PPP frames and HDLC frames is that PPP frames contain protocol and Link Control Protocol (LCP) fields

  • LCP

    • Described in RFCs 1548, 1570, 1661, 2153, and 2484

    • Describes PPP organization and methodology, including basic LCP extensions

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition



Frame format continued
Frame Format (continued)

  • LCP field of the PPP packet can contain many different pieces of information, including the following:

    • Asynchronous character map

    • Maximum receive unit size

    • Compression

    • Authentication

    • Magic number

    • Link Quality Monitoring (LQM)

    • Multilink

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame format continued1
Frame Format (continued)

  • LCP link configuration process

    • Modifies and enhances the default characteristics of a PPP connection

  • Includes the following actions:

    • Link establishment

    • Authentication (optional)

    • Link-quality determination (optional)

    • Network layer protocol configuration negotiation

    • Link termination

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Establishing ppp communications
Establishing PPP Communications

  • Involves the following actions:

    • Link establishment

    • Optional authentication

    • Network layer protocol configuration negotiation

  • The link establishment phase involves the configuration and testing of the data link

  • The authentication process can use two authentication types with PPP connections: PAP and CHAP

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Establishing ppp communications continued
Establishing PPP Communications (continued)

  • PPP is an encapsulation type for serial interface communications

    • To configure a PPP connection, you must access the interface configuration mode for the specific interface you want to configure

  • After LCP has finished negotiating the configuration parameters

    • Network layer protocols can be configured individually by the appropriate NCP

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Establishing ppp communications continued1
Establishing PPP Communications (continued)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Establishing ppp communications continued2
Establishing PPP Communications (continued)

  • Configuring PPP Authentication

    • Using authentication with PPP connections is optional

    • You must specifically configure PPP authentication on each PPP host in order for the host to use it

    • You can choose to enable CHAP, PAP, or both on your PPP connection, in either order

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Establishing ppp communications continued3
Establishing PPP Communications (continued)

  • Once you set the authentication type

    • You must still configure a username and password for the authentication

  • You must exit interface configuration mode and enter global configuration mode

    • Type username followed by the host name of the remote router

    • Then type password followed by the password for that connection

  • Confirming PPP Communications

    • With the show interface command

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition



Establishing ppp communications continued4
Establishing PPP Communications (continued)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame relay standards and equipment
Frame Relay Standards and Equipment

  • Frame Relay

    • A packet switching and encapsulation technology that functions at the Physical and Data Link layers of the OSI reference model

    • A communications technique for sending data over high-speed digital connections

  • ITU-T and ANSI define Frame Relay

    • As a connection between the data terminal equipment (DTE) and the data communications equipment (DCE)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame relay standards and equipment continued
Frame Relay Standards and Equipment (continued)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame relay standards and equipment continued1
Frame Relay Standards and Equipment (continued)

  • The physical equipment that is used on a network may vary from one organization to another

  • Some routers have built-in cards that allow them to make WAN connections

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame relay standards and equipment continued2
Frame Relay Standards and Equipment (continued)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition



Frame relay standards and equipment continued3
Frame Relay Standards and Equipment (continued)

  • Frame Relay access device (FRAD)

    • Network device that connects to the Frame Relay switch

    • Also known as Frame Relay assembler/disassembler

  • Frame Relay network device (FRND)

    • The Frame Relay switch

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Virtual circuits
Virtual Circuits

  • You can use Frame Relay with nearly any serial interface

    • Operates by multiplexing

  • Frame Relay separates each data stream into logical (software-maintained) connections

    • Called virtual circuits

    • Which carry the data transferred on the connection

  • Two types of virtual circuits

    • Switched virtual circuits (SVC)

    • Permanent virtual circuits (PVC)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


DLCI

  • Frame relay connections identify virtual circuits by Data Link Connection Identifier (DLCI) numbers

  • A DLCI number associates an IP address with a specific virtual circuit

  • DLCI numbers have only local significance

  • DLCI numbers are usually assigned by the Frame Relay provider

    • Most likely not the same on either side of the Frame Relay switch

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame relay map
Frame Relay Map

  • Frame Relay map

    • A table in RAM that defines the remote interface to which a specific DLCI number is mapped

  • The definition will contain a DLCI number and an interface identifier

    • Which is typically a remote IP address

  • The Frame Relay map can be built automatically or statically depending on the Frame Relay topology

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition



Frame relay map continued
Frame Relay Map (continued)

  • Subinterfaces

    • Virtual interfaces associated with a physical interface

    • Created by referencing the physical interface followed by a period and a decimal number

  • For the purposes of routing, however, subinterfaces are treated as physical interfaces

  • With subinterfaces, the cost of implementing multiple Frame Relay virtual circuits is reduced

    • Because only one port is required on the router

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


LMI

  • LMI basically extended the functionality of Frame Relay by:

    • Making the DLCIs globally significant rather than locally significant

    • Creating a signaling mechanism between the router and the Frame Relay switch, which could report on the status of the link

    • Supporting multicasting

  • Providing DLCI numbers that are globally significant makes automatic configuration of the Frame Relay map possible

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Lmi continued
LMI (continued)

  • LMI uses keepalive packets to verify the Frame Relay link and to ensure the flow of data

  • Each virtual circuit, represented by its DLCI number, can have one of three connection states:

    • Active

    • Inactive

    • Deleted

  • The Frame Relay switch reports this status information to the Frame Relay map on the local router

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Inverse arp
Inverse ARP

  • In multipoint configurations

    • Routers use the protocol Inverse ARP to send a query using the DLCI number to find a remote IP address

  • As other routers respond to the Inverse ARP queries, the local router can build its Frame Relay map automatically

  • To maintain the Frame Relay map, routers exchange Inverse ARP messages every 60 seconds by default

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Encapsulation types
Encapsulation Types

  • LMI has several different protocol encapsulation types that it can use for management communications

  • Cisco routers support these types of LMI encapsulation:

    • cisco

    • ansi

    • q933a

  • Cisco routers (using IOS Release 11.2 or later) can “autosense” the LMI type used by the Frame Relay switch

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Encapsulation types continued
Encapsulation Types (continued)

  • The basic LMI type has three information elements: report type, keepalive, and PVC status

  • Information concerning the status of the virtual circuit:

    • New

    • Active

    • Receiver not ready

    • Minimum bandwidth

    • Global addressing

    • Multicasting

    • Provider-Initiated Status Update

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Encapsulation types continued1
Encapsulation Types (continued)

  • Split horizon

    • Routing technique that reduces the chance of routing loops on a network

    • Prevents routing update information received on one physical interface from being rebroadcast to other devices through that same physical interface

    • People also refer to this rule as nonbroadcast multiaccess (NBMA)

    • Can cause problems for Frame Relay routing updates

  • The best solution is to configure separate point-to-point subinterfaces for each virtual connection

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition





Performance parameters
Performance Parameters

  • Service contract specifies parameters by which the connection is expected to function:

    • Access rate

    • Committed Information Rate (CIR)

    • Committed Burst Size (CBS)

    • Excess Burst Size (EBS)

    • Oversubscription

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Congestion
Congestion

  • Frame Relay switches attempt to control congestion on the network

  • When the Frame Relay switch recognizes congestion

    • Sends a forward explicit congestion notification (FECN) message to the destination router

  • In addition, the switch sends a backward explicit congestion notification (BECN) message to the transmitting, or source, router

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame format1
Frame Format

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Frame relay topologies
Frame Relay Topologies

  • Frame Relay can use many different WAN topologies:

    • Peer (point-to-point)

    • Star (hub and spoke)

    • Partial mesh

    • Full mesh physical

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition



Frame relay configuration
Frame Relay Configuration

  • In this section, you will learn how to configure Frame Relay over serial interfaces

    • Using IP as the Network layer protocol

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Basic multipoint configuration with two routers
Basic Multipoint Configuration with Two Routers

  • LMI will notify the router about the available DLCI numbers

    • Inverse ARP will build the Frame Relay map dynamically

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition




Basic multipoint configuration with two routers continued
Basic Multipoint Configuration with Two Routers (continued)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Multipoint configuration using a subinterface
Multipoint Configuration Using a Subinterface

  • The Frame Relay map will have to be built statically on RouterA

    • To configure a multipoint subinterface, you map it to multiple remote routers using the same subnet mask, but different DLCI numbers

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Multipoint configuration using a subinterface continued
Multipoint Configuration Using a Subinterface (continued)

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition



Point to point configuration using subinterfaces
Point-to-Point Configuration Using Subinterfaces

  • Point-to-point Frame Relay configurations do not support Inverse ARP

  • You will have to configure each subnet separately

    • Use the frame-relay interface-dlci command to associate the DLCI numbers with a specific subinterface

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition




Frame relay static mapping
Frame Relay Static Mapping

  • Sometimes you have to define the DLCI numbers manually

    • This is called making a static address to DLCI Frame Relay map

  • You statically configure your DLCI entries in the following situations:

    • The remote router does not support Inverse ARP

    • You need to assign specific subinterfaces to specific DLCI connections

    • You want to reduce broadcast traffic

    • You are configuring OSPF over Frame Relay

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Non cisco routers
Non-Cisco Routers

  • Non-Cisco routers use a different Frame Relay encapsulation than Cisco routers

  • If you are configuring Cisco routers to connect to other Cisco routers

    • They will automatically use the Cisco Frame Relay encapsulation

  • If you are connecting a Cisco router to a non-Cisco router, you must specify ietf Frame Relay encapsulation using the following command:

    RouterA(config-if)#encapsulation frame-relay ietf

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Keepalive configuration
Keepalive Configuration

  • By default, keepalive packets are sent out every 10 seconds to the Frame Relay switch

  • You can change the keepalive period by typing keepalive followed by the time in seconds

    RouterA(config-if)#keepalive 15

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Monitoring frame relay
Monitoring Frame Relay

  • You can check your Frame Relay configuration by using show commands

    • These commands allow you to verify that the commands you previously entered produced the desired effect on your router

  • The most common show commands for monitoring Frame Relay operation are:

    show interface

    show frame-relay pvc

    show frame-relay map

    show frame-relay lmi

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition





Summary
Summary

  • Many WAN connectivity options are available for modern networks, including digital lines, Frame Relay, and analog modems

  • The Point-to-Point Protocol (PPP) is the most widely used WAN protocol today

  • PPP provides link establishment, quality determination, Network layer protocol encapsulation, and link termination services

  • Frame relay is a flexible WAN technology that can be used to connect two geographically separate LANs

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Summary continued
Summary (continued)

  • Frame relay is both a service and type of encapsulation

  • Service parameters for Frame Relay include the access rate, Committed Information Rate (CIR), Committed Burst Size (CBS), and Excess Burst Size (EBS)

  • Frame relay connections employ virtual circuits that can be either permanent or switched

  • Virtual circuit connections across Frame Relay connections are defined by Data Link Connection Identifier (DLCI) numbers

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


Summary continued1
Summary (continued)

  • Most Frame Relay providers support LMI, which allows Frame Relay maps to be dynamically created via Inverse ARP

  • Static mappings of DLCI numbers to remote IP addresses can be configured when routers do not support Inverse ARP

  • Inverse ARP is not enabled on point-to-point links because only one path is available

  • Frame relay circuits can be established over serial interfaces or subinterfaces on Cisco routers

CCNA Guide to Cisco Networking Fundamentals, Fourth Edition


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