CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 11-1
Chapter 11
PPP and Frame Relay
At a Glance
Instructor’s Manual Table of Contents
• Overview
• Objectives
• Teaching Tips
• Quick Quizzes
• Class Discussion Topics
• Additional Projects
• Additional Resources
• Key Terms
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 11-2
Lecture Notes
Overview
WAN technologies typically define Physical and Data Link layer connections between
devices. PPP and Frame Relay are both Data Link layer encapsulation types implemented
on a router. In this chapter, you will learn about PPP and Frame Relay. In addition, the
chapter covers the format of PPP data frames, Frame Relay terms, specifications, and
service types. Finally, the chapter demonstrates how to implement and configure PPP and
Frame Relay connections on Cisco routers.
Chapter Objectives
• Describe PPP encapsulation
• Configure PPP encapsulation and its options
• Describe and enable PPP multilink
• Understand Frame Relay standards and equipment
• 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
Teaching Tips
PPP
1. Define PPP as an Internet standard protocol defined in RFCs 2153 and 1661. It provides
point-to-point, router-to-router, host-to–router, and host-to-host connections.
2. Explain that PPP is considered a peer technology based on its point-to-point physical
4. Explain that PPP can be used over several different physical interfaces, including the
following:
a. Asynchronous serial
PPP in the Protocol Stack
1. Explain that you can use PPP over both asynchronous and synchronous connections at
2. Mention that the Link Control Protocol (LCP) is used at the Data Link layer to
establish, configure, and test the connection.
3. Explain that the Network Control Protocols (NCPs) allow the simultaneous use of
Teaching
Tip
Examples of NCPs include IP Control Protocol (IPCP), IPX Control Protocol
(IPXCP), and AppleTalk Control Protocol (ATCP).
Frame Format
1. Explain that PPP is based on the High-Level Data Link Control (HDLC) protocol. The
3. Describe some of the information contained in the LCP field of the PPP packet,
including the following:
a. Asynchronous character map
4. Explain that the LCP link configuration process modifies and enhances the default
characteristics of a PPP connection. It includes the following actions:
a. Link establishment
b. Authentication (optional)
Establishing PPP Communications
1. Mention that establishing PPP communications involves the following actions:
2. Explain that the link establishment phase involves the configuration and testing of the
3. Mention that the authentication process can use two authentication types with PPP
4. Explain that PPP is an encapsulation type for serial interface communications. To
6. Emphasize the point that using authentication with PPP connections is optional. You
7. Mention that once you set the authentication type, you must still configure a username
and password for the authentication. You must exit interface configuration mode and
8. Show how to confirm PPP communication with the show interface command.
Frame Relay Standards and Equipment
1. Define Frame Relay as a packet switching and encapsulation technology that functions
11-7 to illustrate your explanation.
3. Mention that the physical equipment that is used on a network may vary from one
4. Define Frame Relay access device (FRAD) as a network device that connects to the
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 11-5
Virtual Circuits
2. Explain that Frame Relay separates each data stream into logical (software-maintained)
connections, called virtual circuits, which carry the data transferred on the connection.
DLCI
1. Explain that Frame Relay connections identify virtual circuits by Data Link Connection
2. Mention that DLCI numbers have only local significance. DLCI numbers are usually
Frame Relay Map
1. Define Frame Relay map as a table in RAM that defines the remote interface to which a
3. Define subinterfaces as virtual interfaces associated with a physical interface. They are
4. Explain that for the purposes of routing, however, subinterfaces are treated as physical
interfaces.
5. Mention that with subinterfaces, the cost of implementing multiple Frame Relay virtual
Quick Quiz 1
Teaching
Tip
The network administrator typically handles the local connection up to the point
that it enters the PDN. Items that are part of the PDN, including the Frame Relay
switch, fall under the control and responsibility of the telecommunications
provider.
1. ____ is an Internet standard protocol defined in RFCs 2153 and 1661.
2. The ____ process modifies and enhances the default characteristics of a PPP
connection.
3. ____ is a communications technique for sending data over high-speed digital
connections operating at anywhere from 56 Kbps to 44.736 Mbps or higher.
4. A(n) ____ is a table in RAM that defines the remote interface to which a specific DLCI
number is mapped.
LMI
1. Explain that LMI basically extended the functionality of Frame Relay by:
a. Making the DLCIs globally significant rather than locally significant
3. Mention that LMI uses keepalive packets to verify the Frame Relay link and to ensure
the flow of data.
4. Explain that each virtual circuit, represented by its DLCI number, can have one of three
connection states:
5. Mention that the Frame Relay switch reports this status information to the Frame Relay
map on the local router.
Teaching
Tip
Without LMI, the Frame Relay map must be built statically in the routers.
However, by making the DLCIs globally significant, LMI facilitates dynamic
Frame Relay map tables through the use of the Inverse ARP protocol.
Inverse ARP
1. Explain that in multipoint configurations, routers use the protocol Inverse ARP to send
2. Mention that to maintain the Frame Relay map, routers exchange Inverse ARP
messages every 60 seconds by default.
Encapsulation Types
2. Describe the following types of LMI encapsulation supported by Cisco routers:
3. Mention that Cisco routers (using IOS Release 11.2 or later) can “autosense” the LMI
type used by the Frame Relay switch.
5. Describe the information concerning the status of the virtual circuit, including the
following:
a. New
b. Active
c. Receiver not ready
d. Minimum bandwidth
e. Global addressing
f. Multicasting
g. Provider-Initiated Status Update
Teaching
Tip
Frame Relay does not provide error checking, as do other network protocols such
as Synchronous Data Link Control (SDLC). This makes Frame Relay
connections more efficient, but it also means that Frame Relay must rely on the
upper-layer protocols, such as TCP, to provide error correction.
6. Define split horizon as a routing technique that reduces the chance of routing loops on a
network. It prevents routing update information received on one physical interface from
7. Explain that split horizon 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 11-8
Performance Parameters
1. Describe the following performance parameters for Frame Relay connections:
a. Access rate
b. Committed Information Rate (CIR)
Congestion
1. Mention that Frame Relay switches attempt to control congestion on the network.
2. Explain that when the Frame Relay switch recognizes congestion, it sends a forward
Frame Format
1. Use Figure 11-14 to describe the Frame Relay frame format.
Frame Relay Topologies
1. Use Figures 11-15 to describe the following four WAN topologies used by Frame
Relay:
a. Peer (point-to-point)
Frame Relay Configuration
1. In this section, you will learn how to configure Frame Relay over serial interfaces using
Basic Multipoint Configuration with Two Routers
1. Explain that in this case, LMI will notify the router about the available DLCI numbers
and Inverse ARP will build the Frame Relay map dynamically. Use Figures 11-16 and
11-7, and Table 11-1 to illustrate your explanation.
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 11-9
Multipoint Configuration Using a Subinterface
1. Explain that in this case, the Frame Relay map will have to be built statically on
11-2 to illustrate your explanation.
Point-to-Point Configuration Using Subinterfaces
1. Mention that point-to-point Frame Relay configurations do not support Inverse ARP.
Frame Relay Static Mapping
2. Explain that you statically configure your DLCI entries in the following situations:
a. The remote router does not support Inverse ARP
Non-Cisco Routers
1. Mention that non-Cisco routers use a different Frame Relay encapsulation than Cisco
2. Explain that if you are connecting a Cisco router to a non-Cisco router, you must
Keepalive Configuration
1. Mention that by default, keepalive packets are sent out every 10 seconds to the Frame
Relay switch.
2. Explain that you can change the keepalive period by typing keepalive followed by
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 11-10
Monitoring Frame Relay
1. Explain that you can check your Frame Relay configuration by using show commands.
2. Use Figures 11-21 through 11-24 to describe the most common show commands for
monitoring Frame Relay operation:
a. show interface
Quick Quiz 2
1. Frame relay engineers designed ____ in 1990 to enhance standard Frame Relay.
2. LMI uses ____ packets (sent every 10 seconds by default) to verify the Frame Relay
link and to ensure the flow of data.
3. A(n) ____ implementation prevents routing update information received on one
physical interface from being rebroadcast to other devices through that same physical
interface.
4. When the sum of the data arriving over all virtual circuits exceeds the access rate, the
situation is called ____.
Class Discussion Topics
1. What are the main improvements of PPP over SLIP?
2. What is the primary purpose of inverse ARP?
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 11-11
Additional Projects
1. X.25 is an ITU-T standard network layer protocol for packet switched wide area
2. Frame Relay operates by multiplexing. Ask your students to read more about
Additional Resources
2. High-Speed Serial Interface (HSSI)
3. Frame Relay
4. Frame Relay
5. Virtual Circuit
Key Terms
➢ address The element of the PPP frame represented by the binary sequence 11111111;
because PPP is used to create a point-to-point connection, there is no need for PPP to
CCNA Guide to Cisco Networking Fundamentals, Fourth Edition 11-12
➢ compression Data compression that can be performed on the PPP packet at the source
and then uncompressed at the destination.
➢ Consultative Committee on International Telephony and Telegraphy (CCITT) The
former name of International Telecommunication Union-Telecommunication
problems in a production environment.
➢ flag Identifies the beginning and end of the PPP frame.
➢ Frame Check Sequence (FCS) A mathematical computation placed at the end of the
frame; used to ensure that the frame was not corrupted during transmission.
➢ Frame Relay access device (FRAD) The device that the Frame Relay customer uses to
inside the public data network.
➢ Frame Relay switching table A table that is maintained on a Frame Relay switch; used
to route Frame Relay traffic via virtual circuit DLCI numbers.
➢ High-Level Data Link Control (HDLC) A common layer 2 WAN protocol that many
other WAN protocols are based upon.
should be maintained between them.
➢ LCP link configuration A process that modifies and enhances the default
characteristics of a PPP connection; includes the following actions: link establishment,
authentication, link-quality determination, Network layer protocol configuration
negotiation, and link termination.
➢ link termination The process of disconnecting a PPP connection when the call is
complete, which is determined by the PPP hosts that made the connection.
➢ loopback command A Cisco router command that places an interface in a looped-back
state, which means that all outgoing data will be redirected as incoming data without
going out on the network; used for testing purposes.
indicate the type of protocol that is encapsulated.
➢ Network layer protocol configuration negotiation The process of determining a
Network layer protocol to use over a PPP connection that is common to both PPP hosts.
➢ nonbroadcast multiaccess (NBMA) A rule used in Frame Relay that does not allow
broadcasts to be sent to multiple locations from a single interface.
➢ static address to DLCI Frame Relay map A Frame Relay map that has been manually
created by a network administrator.
➢ subinterface A logical division of an interface; for example, a single serial interface
can be divided into multiple logical subinterfaces.
➢ Terminal Access Controller Access Control System (TACACS) An authentication
protocol that allows Cisco routers to offload user administration to a central server.
TACACS and Extended TACACS (XTACACS) are defined in RFC 1492.