ccna ppp and frame relay

CCNA Guide to Cisco Networking Fundamentals

Chapter 11PPP and Frame Relay

CCNA Guide to Cisco Networking Fundamentals 2

Objectives

• Describe PPP encapsulation

• Configure PPP encapsulation and its options

• Describe and enable PPP multilink

• Understand Frame Relay standards and equipment


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


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


PPP (continued)

• PPP can be used over several different physical interfaces, including the following:– Asynchronous serial– ISDN synchronous serial– High-Speed Serial Interface (HSSI)


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


PPP in the Protocol Stack (continued)

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


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


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


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


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



• 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



• 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


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)


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




• 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


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)

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


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


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


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


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


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


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


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


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


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


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



Frame Format

Frame Relay Topologies

• Frame Relay can use many different WAN topologies: – Peer (point-to-point)– Star (hub and spoke)– Partial mesh– Full mesh physical


Frame Relay Configuration

• In this section, you will learn how to configure Frame Relay over serial interfaces– Using IP as the Network layer protocol


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


Basic Multipoint Configuration with Two Routers (continued)


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


Multipoint Configuration Using a Subinterface (continued)


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


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


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



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


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

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


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


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 ppp and frame relay

Technology

cisco networking

cisco networking

cisco networking

excess burst

committed

support inverse

frame relay

establishing