1. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE I Chapter 6 1 Point-to-Point Protocol (PPP) Accessing the WAN – Chapter 2

2. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 2 Objectives  Describe the fundamental concepts of point-to-point serial communication including TDM, demarcation point, DTE-DCE functions, HDLC encapsulation, and serial interface troubleshooting.  Describe PPP concepts including PPP layered architecture, PPP frame structure, PPP session establishment, multiprotocol encapsulation support, link control protocol (LCP), network control protocol (NCP), and Internet Protocol Control Protocol (IPCP).  Configure PPP on a serial interface including enabling PPP encapsulation, verifying the PPP connection and troubleshooting encapsulation problems.  Configure PPP authentication including explaining PAP and CHAP authentication protocols, configuring PPP authentication using PAP and CHAP, and troubleshooting PPP authentication problems.

3. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 3 Fundamental Concepts of Point-to-Point Serial Communication  Concept of serial communication as the basis of WAN technologies

4. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 4 Serial Communication Standards  All long-haul communications and most computer networks use serial connections, because  the cost of cable and synchronization difficulties make parallel connections impractical.  The most significant advantage is simpler wiring.  Also, serial cables can be longer than parallel cables, because there is much less interaction (crosstalk) among the conductors in the cable.

5. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 5  Time Division Multiplexing  TDM is a Physical layer concept. It has no regard for the nature of the information that is being multiplexed onto the output channel.  Statistical Time Division Multiplexing  To overcome the inefficiency of TDM, STDM was introduced as in TDM the slot remains empty if no data to transmit at the sender side.

6. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 6 Describe the Fundamental Concepts of Point-to-Point Serial Communication  How two or more data streams are transported across a single physical connection using TDM

7. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 7 DTE-DCE –A serial connection has a DTE device at one end of the connection and a DCE device at the other end. The connection between the two DCE devices is the WAN service provider transmission network. In this case: –The CPE, which is generally a router, is the DTE. The DTE could also be a terminal, computer, printer, or fax machine if they connect directly to the service provider network. –The DCE, commonly a modem or CSU/DSU, is the device used to convert the user data from the DTE into a form acceptable to the WAN service provider transmission link. This signal is received at the remote DCE, which decodes the signal back into a sequence of bits. The remote DCE then signals this sequence to the remote DTE.

8. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 8 HDLC Encapsulation  WAN Encapsulation Protocols  To ensure that the correct protocol is used, you need to configure the appropriate Layer 2 encapsulation type. The choice of protocol depends on the WAN technology and the communicating equipment.  HDLC - The default encapsulation type on point-to-point connections, dedicated links, and circuit-switched connections when the link uses two Cisco devices.  PPP - Provides router-to-router and host-to-network connections  Serial Line Internet Protocol (SLIP) - A standard protocol for point-to- point serial connections using TCP/IP. SLIP has been largely displaced by PPP.

9. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 9 Conti…  Frame Relay - Industry standard, switched, Data Link layer protocol that handles multiple virtual circuits. Frame Relay is a next generation protocol after X.25.  ATM - The international standard for cell relay in which devices send multiple service types (such as voice, video, or data) in fixed-length (53- byte) cells. Fixed-length cells allow processing to occur in hardware, thereby reducing transit delays.

10. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 10 HDLC Encapsulation  Flag - The flag field initiates and terminates error checking. The frame always starts and ends with an 8-bit flag field. The bit pattern is 01111110.  Address - The address field contains the HDLC address of the secondary station. This address can contain a specific address, a group address, or a broadcast address. A primary address is either a communication source or a destination, which eliminates the need to include the address of the primary.  Control - The control field uses three different formats, –Information (I) frame: I-frames carry upper layer information and some control information. –Supervisory (S) frame: S-frames provide control information. An S-frame can request and suspend transmission, report on status, and acknowledge receipt of I-frames. –Unnumbered (U) frame: U-frames support control purposes

11. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 11  Protocol-(only used in Cisco HDLC) This field specifies the protocol type encapsulated within the frame  Data-The data field contains a path information unit (PIU) or exchange identification (XID) information.  Frame check sequence (FCS)-The FCS precedes the ending flag delimiter and is usually a cyclic redundancy check (CRC) calculation remainder.

12. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 12 Configuring HDLC Encapsulation  Router (config-if)# encapsulation hdlc

13. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 13 Trouble shooting the Serial Interface  show interfaces serial  show controllers  Cisco 7000 series routers use a cBus controller card for connecting serial links. With these routers, use the  show controllers cbus command.

14. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 14 PPP  What is PPP?  Recall that HDLC is the default serial encapsulation method when you connect two Cisco routers.  With an added protocol type field, the Cisco version of HDLC is proprietary.  Thus, Cisco HDLC can only work with other Cisco devices.  However, when you need to connect to a non-Cisco router, you should use PPP encapsulation.

15. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 15 Conti…  PPP encapsulates data frames for transmission over Layer 2 physical links.  PPP establishes a direct connection using serial cables, phone lines, trunk lines, cellular telephones, specialized radio links, or fiber-optic links.  There are many advantages to using PPP, including the fact that it is not proprietary.  The link quality management feature monitors the quality of the link. If too many errors are detected, PPP takes the link down.  PPP supports PAP and CHAP authentication.

16. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 16 Conti…  Purpose and format of each of the fields in a PPP frame

17. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 17 Point-to-Point Concepts  Three phases of PPP session establishment

18. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 18 PPP Configuration Options  PPP can be configured to support various functions including:  Authentication using either PAP or CHAP  Compression using either Stacker or Predictor  Error Detection  Multilink which combines two or more channels to increase the WAN bandwidth

19. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 19 PPP Configuration Commands  R3#configure terminal  R3(config)#interface serial 0/0/0  R3(config-if)#encapsulation ppp  Compression  R3(config-if)#compress [predictor | stac]  Quality  R3(config-if)#ppp quality 80  Multilink  Router(config-if)#ppp multilink –this command perform load balancing  Verification-- show interfaces serial  Debug-Packet, negotiation, authentication, compression, etc

20. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 20 PPP Authentication Protocol  Password Authentication Protocol (PAP)  Initiating PAP PAP provides a simple method for a remote node to establish its identity using a two-way handshake.  Command is ppp authentication pap  username name password password  It must match the user name and password of the other router.

21. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 21 Conti…  Challenge Handshake Authentication Protocol (CHAP)  Unlike PAP, which only authenticates once, CHAP conducts periodic challenges to make sure that the remote node still has a valid password value.

22. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 22 Configuring PPP with Authentication  Differentiate between PAP and CHAP

23. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 23 Configuring PPP with Authentication  Describe how to use PAP to authenticate a PPP connection

24. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 24 Configuring PPP with Authentication  Describe how to use CHAP to authenticate a PPP connection

25. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 25 Configuring PPP with Authentication  Explain how to configure a PPP connection with authentication

26. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 26 Configuring PPP with Authentication  Explain the output of the debug ppp authentication command

27. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 27 Summary  PPP is a widely used WAN protocol  PPP provides multi-protocol LAN to WAN connections  PPP session establishment – 4 phases Link establishment Link quality determination Network layer protocol configuration negotiation Link termination  WAN Encapsulation –HDLC default encapsulation –PPP

28. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 28 Summary  PPP authentication –PAP 2 way handshake –CHAP 3 way handshake –Use debug ppp authentication to confirm authentication configuration  PPP configuration –Done on a serial interface  After PPP configuration, use show interfaces command to display: –LCP state –NCP state

29. © 2006 Cisco Systems, Inc. All rights reserved.Cisco PublicITE 1 Chapter 6 29