Quản trị mạng - Chapter 2: PPP

1Chapter 2 – PPP CCNA Exploration 4.0 Học viện mạng Bach Khoa - Website: www.bkacad.com 2 Introduction Học viện mạng Bach Khoa - Website: www.bkacad.com 3 Serial Point-to-Point Links Học viện mạng Bach Khoa - Website: www.bkacad.com 4 Introducing Serial Communications • Computers make use of relatively short parallel connections between interior components, but use a serial bus to convert signals for most external communications. Học viện mạng Bach Khoa - Website: www.bkacad.com 5 Introducing Serial Communications • In a parallel connection, it is wrong to assume that the 8 bits leaving the sender at the same time arrive at the receiver at the same time. Rather, some of the bits get there later than others. This is known as clock skew. Học viện mạng Bach Khoa - Website: www.bkacad.com 6 Introducing Serial Communications • Parallel wires are physically bundled in a parallel cable, and signals can imprint themselves on each other. The possibility of crosstalk across the wires requires more processing, especially at higher frequencies. Học viện mạng Bach Khoa - Website: www.bkacad.com 7 Introducing Serial Communications • 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. Học viện mạng Bach Khoa - Website: www.bkacad.com 8 Introducing Serial Communications Học viện mạng Bach Khoa - Website: www.bkacad.com 9 TDM • Time Division Multiplexing – Bell Laboratories invented time-division multiplexing (TDM) to maximize the amount of voice traffic carried over a medium. – TDM divides the bandwidth of a single link into separate channels or time slots. – TDM transmits two or more channels over the same link by allocating a different time interval (time slot) for the transmission of each channel. Học viện mạng Bach Khoa - Website: www.bkacad.com 10 TDM • Statistical Time Division Multiplexing (STDM) – STDM uses a variable time slot length allowing channels to compete for any free slot space. It employs a buffer memory that temporarily stores the data during periods of peak traffic. – STDM does not waste high-speed line time with inactive channels using this scheme. Học viện mạng Bach Khoa - Website: www.bkacad.com 11 TDM Examples Học viện mạng Bach Khoa - Website: www.bkacad.com 12 TDM Examples Học viện mạng Bach Khoa - Website: www.bkacad.com 13 Demarcation Point Học viện mạng Bach Khoa - Website: www.bkacad.com 14 DTE-DCE • 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. Học viện mạng Bach Khoa - Website: www.bkacad.com 15 Cable Standards • The DTE/DCE interface for a particular standard defines the following specifications: – Mechanical/physical - Number of pins and connector type – Electrical - Defines voltage levels for 0 and 1 – Functional - Specifies the functions that are performed by assigning meanings to each of the signaling lines in the interface – Procedural - Specifies the sequence of events for transmitting data Học viện mạng Bach Khoa - Website: www.bkacad.com 16 Cable Standards Học viện mạng Bach Khoa - Website: www.bkacad.com 17 Cable Standards Học viện mạng Bach Khoa - Website: www.bkacad.com 18 Parallel to Serial Conversion • Your PC also has a Universal Asynchronous Receiver/Transmitter (UART) chip on the motherboard. Since the data in your PC flows along parallel circuits, the UART chip converts the groups of bits in parallel to a serial stream of bits. • To work faster, a UART chip has buffers so it can cache data coming from the system bus while it processes data going out the serial port. • The UART is the DTE agent of your PC and communicates with the modem or other serial device, which, in accordance with the RS-232C standard, has a complementary interface called the DCE interface. Học viện mạng Bach Khoa - Website: www.bkacad.com 19 HDLC Encapsulation • HDLC - The default encapsulation type on point-to-point connections, dedicated links, and circuit-switched connections when the link uses two Cisco devices. HDLC is now the basis for synchronous PPP used by many servers to connect to a WAN, most commonly the Internet. Học viện mạng Bach Khoa - Website: www.bkacad.com 20 HDLC Encapsulation Học viện mạng Bach Khoa - Website: www.bkacad.com 21 Configuring HDLC Encapsulation • Cisco HDLC is the default encapsulation method used by Cisco devices on synchronous serial lines. • You use Cisco HDLC as a point-to-point protocol on leased lines between two Cisco devices. If you are connecting to a non-Cisco device, use synchronous PPP. Học viện mạng Bach Khoa - Website: www.bkacad.com 22 Troubleshooting a Serial Interface • You can identify any of the following five possible problem states in the interface status line: 1. Serial x is down, line protocol is down 2. Serial x is up, line protocol is down 3. Serial x is up, line protocol is up (looped) 4. Serial x is up, line protocol is down (disabled) 5. Serial x is administratively down, line protocol is down Học viện mạng Bach Khoa - Website: www.bkacad.com 23 Troubleshooting a Serial Interface Học viện mạng Bach Khoa - Website: www.bkacad.com 24 Troubleshooting a Serial Interface • The command syntax varies, depending on the platform. Cisco 7000 series routers use a cBus controller card for connecting serial links. With these routers, use the show controllers cbus command. Học viện mạng Bach Khoa - Website: www.bkacad.com 25 Troubleshooting a Serial Interface Học viện mạng Bach Khoa - Website: www.bkacad.com 26 Troubleshooting a Serial Interface Học viện mạng Bach Khoa - Website: www.bkacad.com 27 Troubleshooting a Serial Interface Học viện mạng Bach Khoa - Website: www.bkacad.com 28 Troubleshooting a Serial Interface Học viện mạng Bach Khoa - Website: www.bkacad.com 29 Troubleshooting a Serial Interface • Activity 2.1.7.3 Học viện mạng Bach Khoa - Website: www.bkacad.com 30 Troubleshooting a Serial Interface • Activity 2.1.7.3 Học viện mạng Bach Khoa - Website: www.bkacad.com 31 Troubleshooting a Serial Interface • Activity 2.1.7.3 Học viện mạng Bach Khoa - Website: www.bkacad.com 32 Troubleshooting a Serial Interface • Activity 2.1.7.3 Học viện mạng Bach Khoa - Website: www.bkacad.com 33 PPP Concepts Học viện mạng Bach Khoa - Website: www.bkacad.com 34 Introducing PPP • What is PPP? – Cisco HDLC is the default serial encapsulation method when you connect two Cisco routers. – When you need to connect to a non-Cisco router, you should use PPP encapsulation. – PPP establishes a direct connection using serial cables, phone lines, trunk lines, cellular telephones, specialized radio links, or fiber-optic links. – There are many features not available in HDLC: • 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. This feature is explained and practiced in a later section. PPP contains 3 main components: 1. HDLC protocol for encapsulating datagrams over point-to-point links. 2. Extensible Link Control Protocol (LCP) to establish, configure, and test the data link connection. 3. Family of Network Control Protocols (NCPs) for establishing and configuring different network layer protocols. Học viện mạng Bach Khoa - Website: www.bkacad.com 35 PPP Layered Architecture • At the physical layer, you can configure PPP on a range of interfaces, including: – Asynchronous serial – Synchronous serial – HSSI – ISDN Học viện mạng Bach Khoa - Website: www.bkacad.com 36 PPP Architecture - Link Control Protocol Layer • The LCP provides automatic configuration of the interfaces at each end, including: – Handling varying limits on packet size – Detecting common misconfiguration errors – Terminating the link – Determining when a link is functioning properly or when it is failing • PPP also uses the LCP to agree automatically on encapsulation formats (authentication, compression, error detection) as soon as the link is established. Học viện mạng Bach Khoa - Website: www.bkacad.com 37 PPP Architecture - Network Control Protocol Layer Học viện mạng Bach Khoa - Website: www.bkacad.com 38 PPP Frame Structure Học viện mạng Bach Khoa - Website: www.bkacad.com 39 Establishing a PPP Session • Phase 1: Link establishment and configuration negotiation • Phase 2: Link quality determination (optional) • Phase 3: Network layer protocol configuration negotiation Học viện mạng Bach Khoa - Website: www.bkacad.com 40 Extra: PPP Session Establishment (Detail) 1. Link establishment - (LCPs) 2. Authentication - Optional (LCPs) 3. Link quality determination - Optional (LCPs) 4. Network layer protocol configuration (NCPs) 5. Link termination (LCPs) Học viện mạng Bach Khoa - Website: www.bkacad.com 41 Establishing a Link with LCP • LCP operation uses three classes of LCP frames to accomplish the work of each of the LCP phases: – Link-establishment frames establish and configure a link (Configure-Request, Configure-Ack, Configure-Nak, and Configure-Reject) – Link-maintenance frames manage and debug a link (Code-Reject, Protocol-Reject, Echo-Request, Echo-Reply, and Discard-Request) – Link-termination frames terminate a link (Terminate-Request and Terminate-Ack) Học viện mạng Bach Khoa - Website: www.bkacad.com 42 Establishing a Link with LCP Học viện mạng Bach Khoa - Website: www.bkacad.com 43 LCP Packet Học viện mạng Bach Khoa - Website: www.bkacad.com 44 LCP Packet Học viện mạng Bach Khoa - Website: www.bkacad.com 45 PPP Configuration Options • PPP can be configured to support various functions including: 1. Authentication using either PAP or CHAP 2. Compression using either Stacker or Predictor 3. Multilink which combines two or more channels to increase the WAN bandwidth Học viện mạng Bach Khoa - Website: www.bkacad.com 46 PPP Configuration Options Học viện mạng Bach Khoa - Website: www.bkacad.com 47 NCP Explained Học viện mạng Bach Khoa - Website: www.bkacad.com 48 NCP Explained • Activity 2.2.6.2 Học viện mạng Bach Khoa - Website: www.bkacad.com 49 NCP Explained • Activity 2.2.6.2 Học viện mạng Bach Khoa - Website: www.bkacad.com 50 NCP Explained • Activity 2.2.6.2 Học viện mạng Bach Khoa - Website: www.bkacad.com 51 Configuring PPP Học viện mạng Bach Khoa - Website: www.bkacad.com 52 PPP Configuration Options • PPP may include the following LCP options: – Authentication – Compression – Error Detection – Multilink – PPP Callback Học viện mạng Bach Khoa - Website: www.bkacad.com 53 PPP Configuration Commands Học viện mạng Bach Khoa - Website: www.bkacad.com 54 PPP Configuration Commands • Example 1: Enabling PPP on an Interface – R3#configure terminal – R3(config)#interface serial 0/0 – R3(config-if)#encapsulation ppp • Example 2: Compression – R3(config)#interface serial 0/0 – R3(config-if)#encapsulation ppp – R3(config-if)#compress [predictor | stac] • Example 3: Link Quality Monitoring – R3(config)#interface serial 0/0 – R3(config-if)#encapsulation ppp – R3(config-if)#ppp quality 80 • Example 4: Load Balancing Across Links – Router(config)#interface serial 0/0 – Router(config-if)#encapsulation ppp – Router(config-if)#ppp multilink Học viện mạng Bach Khoa - Website: www.bkacad.com 55 Extra: More Information on Compression Cisco supports these types of compression: • 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. • MPPC-This protocol (RFC 2118) allows Cisco routers to exchange compressed data with Microsoft clients. MPPC uses an LZ-based compression algorithm. • TCP header compression-This type of compression is used to compress the TCP headers. Học viện mạng Bach Khoa - Website: www.bkacad.com 56 Extra: More Information on Compression Important notes on compression: – The highest compression ratio is usually reached with highly compressible text files. – Already compressed files such as JPEG graphics or MPEG files, or files that were compressed with software such as PKZIP or StuffIt, are only compressed 1:1, or even less. – Trying to compress already compressed data can take longer than transferring the data without compression. – Compressing data can cause performance degradation because it is software, not hardware compression. – Compression can be CPU or memory intensive. – Predictor is more memory intensive and less CPU intensive, whereas Stacker and MPPC are more CPU intensive and less memory intensive. Memory intensive means that an extra memory allowance is required. Học viện mạng Bach Khoa - Website: www.bkacad.com 57 Extra: Enable Link Quality Monitoring (LQM) • Link Quality Monitoring (LQM) is available on all serial interfaces running PPP. LQM will monitor the link quality, and if the quality drops below a configured percentage, the router shuts down the link. • The percentages are calculated for both the incoming and outgoing directions. – The outgoing quality is calculated by comparing the total number of packets and bytes sent with the total number of packets and bytes received by the destination node. – The incoming quality is calculated by comparing the total number of packets and bytes received with the total number of packets and bytes sent by the destination peer. • When LQM is enabled, Link Quality Reports (LQRs) are sent, in place of keepalives, every keepalive period. All incoming keepalives are responded to properly. If LQM is not configured, keepalives are sent every keepalive period and all incoming LQRs are responded to with an LQR. • LQR is specified in RFC 1989, PPP Link Quality Monitoring, by William A. Simpson of Computer Systems Consulting Services. Học viện mạng Bach Khoa - Website: www.bkacad.com 58 Verifying a Serial PPP Encapsulation Configuration Học viện mạng Bach Khoa - Website: www.bkacad.com 59 Troubleshooting PPP Encapsulation Học viện mạng Bach Khoa - Website: www.bkacad.com 60 Troubleshooting PPP Encapsulation Học viện mạng Bach Khoa - Website: www.bkacad.com 61 Troubleshooting PPP Encapsulation Học viện mạng Bach Khoa - Website: www.bkacad.com 62 Troubleshooting PPP Encapsulation Học viện mạng Bach Khoa - Website: www.bkacad.com 63 Configuring PPP with Authentication Học viện mạng Bach Khoa - Website: www.bkacad.com 64 PPP Authentication Protocols • The authentication phase of a PPP session is optional. If used, you can authenticate the peer after the LCP establishes the link and choose the authentication protocol. If it is used, authentication takes place before the network layer protocol configuration phase begins. Học viện mạng Bach Khoa - Website: www.bkacad.com 65 Password Authentication Protocol (PAP) Học viện mạng Bach Khoa - Website: www.bkacad.com 66 Challenge Handshake Authentication Protocol (CHAP) • Initiating CHAP • Responding CHAP • • Completing CHAP Học viện mạng Bach Khoa - Website: www.bkacad.com 67 PPP Encapsulation and Authentication Process Học viện mạng Bach Khoa - Website: www.bkacad.com 68 Học viện mạng Bach Khoa - Website: www.bkacad.com 69 Configuring PPP with Authentication Học viện mạng Bach Khoa - Website: www.bkacad.com 70 Học viện mạng Bach Khoa - Website: www.bkacad.com 71 Học viện mạng Bach Khoa - Website: www.bkacad.com 72 Notes: - sent-username and passwordmust match remote username and password. - Passwords are case-sensitive, but usernames are not. - Hostnames are not involved. Example: Configuring PAP 172.25.3.0/24 Serial .1/S0.2/S0 DCEDTE hostname SantaCruz username HQ password HQpass interface Serial0 ip address 172.25.3.2 255.255.255.0 encapsulation ppp ppp authentication pap ppp pap sent-username SantaCruz password SantaCruzpass hostname HQ username SantaCruz password SantaCruzpass interface Serial0 ip address 172.25.3.1 255.255.255.0 encapsulation ppp ppp authentication pap ppp pap sent-username HQ password HQpass Học viện mạng Bach Khoa - Website: www.bkacad.com 73 Extra: One-way PAP authentication (config)# hostname RA (config)# interface serial 0 encapsulation ppp ppp pap sent-username RA-X password CISCO-X (config)# hostname RB (config)# username RA-X password CISCO-X (config)# interface serial 0 encapsulation ppp ppp authentication pap Học viện mạng Bach Khoa - Website: www.bkacad.com 74 Extra: Two-way PAP authentication (config)# hostname RA (config)# username RB-X password CISCO-B (config)# interface serial 0 encapsulation ppp ppp authentication pap ppp pap sent-username RA-X password CISCO-A (config)# hostname RB (config)# username RA-X password CISCO-A (config)# interface serial 0 encapsulation ppp ppp authentication pap ppp pap sent-username RB-X password CISCO-B Học viện mạng Bach Khoa - Website: www.bkacad.com 75 Notes: - Hostnames are involved unless the ppp chap hostname command is used, and must match remote router’s username command (not case-sensitive). - Passwords are case-sensitive and must match Example: Configuring CHAP 172.25.3.0/24 Serial .1/S0.2/S0 DCEDTE hostname SantaCruz username HQ password boardwalk ppp chap hostname SantaCruz (optional) interface Serial0 ip address 172.25.3.2 255.255.255.0 encapsulation ppp ppp authentication chap hostname HQ username SantaCruz password boardwalk ppp chap hostname HQ (optional) interface Serial0 ip address 172.25.3.1 255.255.255.0 encapsulation ppp ppp authentication chap Học viện mạng Bach Khoa - Website: www.bkacad.com 76 Extra: One-way CHAP authentication (config)# hostname RA-X (config)# username RB password CISCO (config)# interface serial 0 encapsulation ppp OR (config)# hostname RA (config)# interface serial 0 encapsulation ppp ppp chap hostname RA-X ppp chap password CISCO (config)# hostname RB (config)# username RA-X password CISCO (config)# interface serial 0 encapsulation ppp ppp authentication chap Học viện mạng Bach Khoa - Website: www.bkacad.com 77 Troubleshooting a PPP Configuration with Authentication • In the last line, the code = 4 means a failure has occurred. Other code values are as follows: – 1 = Challenge – 2 = Response – 3 = Success – 4 = Failure Học viện mạng Bach Khoa - Website: www.bkacad.com 78 Extra: Configuring PPP Multilink (MLP) Router(config)#interface serial 0/0 Router(config-if)#encapsulation ppp Router(config-if)#ppp multilink • In some environments, it may be necessary to bundle multiple serial links to act as single link with aggregated bandwidth. • Multilink PPP provides load balancing over the router interfaces that PPP uses. Học viện mạng Bach Khoa - Website: www.bkacad.com 79 Extra: Configuring PPP Multilink hostname SantaCruz multilink Virtual-Template 1 interface loopback 0 ip address 192.168.1.1 255.255.255.0 interface Virtual-Template1 ip unnumbered loopback0 ppp multilink interface Serial0 no ip address encapsulation ppp ppp multilink interface Serial1 no ip address encapsulation ppp ppp multilink interface Serial2 no ip address encapsulation ppp ppp multilink hostname HQ multilink Virtual-Template 1 interface loopback 0 ip address 192.168.1.2 255.255.255.0 interface Virtual-Template1 ip unnumbered loopback0 ppp multilink interface Serial0 no ip address encapsulation ppp ppp multilink interface Serial1 no ip address encapsulation ppp ppp multilink interface Serial2 no ip address encapsulation ppp ppp multilink Học viện mạng Bach Khoa - Website: www.bkacad.com 80 Extra: Configuring PPP Multilink (config)# interface Multilink 1 ip address 1.2.3.4 255.255.255.0 ppp multilink (config)# interface Serial 0/0 no ip address encapsulation ppp ppp multilink ppp multilink group 1 (config)# interface Serial 0/1 no ip address encapsulation ppp ppp multilink ppp multilink group 1 Host Route Học viện mạng Bach Khoa - Website: www.bkacad.com 81 Học viện mạng Bach Khoa - Website: www.bkacad.com 82 Labs Học viện mạng Bach Khoa - Website: www.bkacad.com 83 Summary PAP (1-way) • Hostname ISP • Username vnn1234 password vnn1234 • Interface s0/0/0 – Encapsulation ppp – Ppp authentication pap – Ip address 192.168.1.1 255.255.255.0 – Clock rate 128000 • Hostname Cust • Interface s0/0/1 – Encapsulation ppp – Ppp pap sent-username vnn1234 password vnn1234 – Ip address 192.168.1.2 255.255.255.0 Học viện mạng Bach Khoa - Website: www.bkacad.com 84 PAP (2-way) • Hostname ISP • Username vnn1234 password vnn1234 • Interface s0/0/0 – Encapsulation ppp – Ppp authentication pap – Ppp pap sent-username cisco1234 password cisco1234 – Ip address 192.168.1.1 255.255.255.0 – Clock rate 128000 • Hostname Cust • Username cisco1234 password cisco1234 • Interface s0/0/1 – Encapsulation ppp – Ppp authentication pap – Ppp pap sent-username vnn1234 password vnn1234 – Ip address 192.168.1.2 255.255.255.0 Học viện mạng Bach Khoa - Website: www.bkacad.com 85 CHAP (1-way) • Hostname ISP • Username Cust password vnn1234 • Interface s0/0/0 – Encapsulation ppp – Ppp authentication chap • Hostname Cust • Username ISP password vnn1234 • Interface s0/0/1 – Encapsulation ppp Học viện mạng Bach Khoa - Website: www.bkacad.com 86 CHAP (1-way) • Hostname R1 • Username R2 password vnn1268 • Interface s0/0/0 – Encapsulation ppp • Hostname R2 • Username R1 password vnn1268 • Interface s0/0/1 – Encapsulation ppp – Ppp authentication chap Học viện mạng Bach Khoa - Website: www.bkacad.com 87 CHAP (2-way) • Hostname R1 • Username R2 password vnn1268 • Interface s0/0/0 – Encapsulation ppp – Ppp authentication chap • Hostname R2 • Username R1 password vnn1268 • Interface s0/0/1 – Encapsulation ppp – Ppp authentication chap Học viện mạng Bach Khoa - Website: www.bkacad.com 88 PAP (1-way) • R2 (server) • username Customer password 0 cisco123 • interface Serial0/1 • ip address 192.168.1.2 255.255.255.0 • encapsulation ppp • clock rate 2000000 • ppp authentication pap • R1 (client) • interface Serial0/0 • ip address 192.168.1.1 255.255.255.0 • encapsulation ppp • ppp pap sent-username Customer password 0 cisco123 Học viện mạng Bach Khoa - Website: www.bkacad.com 89 PAP(2-way) • R1 • username Customer2 password 0 class123 • interface Serial0/0 • ip address 192.168.1.1 255.255.255.0 • encapsulation ppp • ppp authentication pap • ppp pap sent-username Customer1 password 0 cisco123 • R2 • username Customer1 password 0 cisco123 • interface Serial0/1 • ip address 192.168.1.2 255.255.255.0 • encapsulation ppp • ppp authentication pap – ppp pap sent-username Customer2 password 0 class123 Học viện mạng Bach Khoa - Website: www.bkacad.com 90 CHAP(1-way) (a) • R1 (client) • username R2 password cisco123 • interface Serial0/0 • ip address 192.168.1.1 255.255.255.0 • encapsulation ppp • R2 (server) • username R1 password cisco123 • interface Serial0/1 • ip address 192.168.1.2 255.255.255.0 • encapsulation ppp • ppp authentication chap Học viện mạng Bach Khoa - Website: www.bkacad.com 91 CHAP(1-way) (b) • R1 (client, customer) • No username password • interface Serial0/0 • ip address 192.168.1.1 255.255.255.0 • encapsulation ppp • ppp chap hostname vnn1234 • ppp chap password user1234 • R2 (server, ISP) • username vnn1234 password user1234 • interface Serial0/1 • ip address 192.168.1.2 255.255.255.0 • encapsulation ppp • ppp authentication chap Học viện mạng Bach Khoa - Website: www.bkacad.com 92 CHAP(1-way) (b) • Cust (client, customer) • interface Serial0/0/1 • ip address 192.168.1.1 255.255.255.0 • encapsulation ppp • ppp chap hostname vnn1234 • ppp chap password vnn1234 • ISP (server, ISP) • username vnn1234 password vnn1234 • interface Serial0/0/1 • ip address 192.168.1.2 255.255.255.0 • encapsulation ppp • ppp authentication chap Học viện mạng Bach Khoa - Website: www.bkacad.com 93 CHAP/PAP (1-way) (b) • R1 (client, customer) • No username password • interface Serial0/0/0 • ip address 192.168.1.1 255.255.255.0 • encapsulation ppp • ppp chap hostname vnn1268 • ppp chap password vnn1268 • ppp pap sent-username vnn1268 password vnn1268 • R2 (server, ISP) • username vnn1268 password vnn1268 • interface Serial0/0/1 • ip address 192.168.1.2 255.255.255.0 • encapsulation ppp • ppp authentication chap pap Học viện mạng Bach Khoa - Website: www.bkacad.com 94 •Debug ppp authentication •Debug ppp negotiation Học viện mạng Bach Khoa - Website: www.bkacad.com 95