Chapter 2 Point-to-Point Connections.pdf

7/9/2024 Connecting Networks v6.0 Chapter 2 Point-to-Point Connections H.Swaih...

7/9/2024 Connecting Networks v6.0 Chapter 2 Point-to-Point Connections H.Swaih 1 Chapter 2 - Sections & Objectives 2.1 Serial Point-to-Point Overview Configure HDLC encapsulation. Explain the fundamentals of point-to-point serial communication across a WAN. Configure HDLC encapsulation on a point-to-point serial link. 2.2 PPP Operation Explain how PPP operates across a point-to-point serial link. Compare PPP and HDLC. Explain the PPP-layered architecture and the functions of LCP and NCP. Explain how PPP establishes a session. H.Swaih 2 1  7/9/2024 Chapter 2 - Sections & Objectives (Cont.) 2.3 PPP Implementation Configure PPP encapsulation. Configure PPP encapsulation on a point-to-point serial link. Configure PPP authentication. 2.4 Troubleshoot WAN Connectivity Troubleshoot PPP. Troubleshoot PPP using show and debug commands. H.Swaih 3 Serial Point-to-Point Overview H.Swaih 4 2  7/9/2024 Serial Communications Serial and Parallel Ports Serial Point-to-Point Connection A WAN is owned by a service provider and a LAN is typically owned by an organization. Point-to-point connections are used to connect LANs to service provider WANs. – Also referred to as a serial connection or leased-line connection. Pay for a continuous connection between two remote sites Reserved circuit H.Swaih 5 Serial Communications Serial and Parallel Ports (Cont.) Serial Communication  On most PCs, parallel ports and RS-232 serial ports have been  Method of data transmissions in which the bits are transmitted replaced by the higher speed sequentially (i.e one bit at a time) over a single channel. serial Universal Serial Bus parallel communication (USB) interfaces.  parallel communication transmits multiple bits simultaneously over multiple wires. H.Swaih 6 3  7/9/2024 Serial Communications Serial and Parallel Ports (Cont.) Serial vs Parallel Communications Serial Communication – They use a lower data transfer rate. – Serial ports require fewer wires, often only 3 (Tx, Rx, Ground). While it's true that the core serial communication only requires 3 signals - transmit (Tx), receive (Rx), and ground (GND) - the physical serial port connectors typically have more pins. The most common serial port standard is RS-232, which typically has the following pin configuration: 9-pin D-sub connector: – Pin 1: DCD (Data Carrier Detect) , Pin 2: RxD (Receive Data), Pin 3: TxD (Transmit Data), Pin 4: DTR (Data Terminal Ready), Pin 5: GND (Ground), Pin 6: DSR (Data Set Ready), Pin 7: RTS (Request to Send), Pin 8: CTS (Clear to Send),Pin 9: RI (Ring Indicator) – Common uses include connecting modems, mice, and older computer peripherals. – Examples include RS-232, RS-422, and RS-485 serial port standards.  parallel communication ꟷ They have a higher data transfer rate, typically up to several megabits per second. – Parallel ports require more wires, often 8 or more data lines. – Common uses include connecting printers, scanners, and other high-speed peripherals. H.Swaih 7 Serial Communications Point-to-Point Communication Links  Point-to-point link  Used when permanent dedicated connections are required  Provides a single, pre-established WAN communications path  Path goes from the customer premises, through the provider network, to a remote destination, as shown in the figure  Can connect two geographically distant sites, such as a corporate office in New York and a regional office in London  Not limited to connections that cross land (undersea fiber-optics)  Usually more expensive than shared services  Constant availability is essential for some applications such as VoIP or video over IP. H.Swaih 8 Voice Over IP 4  7/9/2024 Serial Communications Serial Bandwidth  Bandwidth  In North America, expressed as a digital signal  Refers to the rate at which data is transferred level number (DS0, DS1, etc.), which refers to over the communication link. the rate and format of the signal (See next sildes 9 & 10).  Carrier technology will dictate how much  Most fundamental line speed is 64 kb/s, or bandwidth is available. DS0. one channel  North American (T-carrier) specification  24 DS0s can be bundled to get a DS1 line (T1  European (E-carrier) system line).  U.S. Optical Carrier (OC) bandwidth points  28 DS1s can be bundled to get a DS3 line (T3 line).  OC transmission rates are a set of standardized 28*24=672channel each one 64kb/s specifications for the transmission of digital bandwidth=672*64k=43Mb/s signals carried on SONET fiber-optic networks. H.Swaih 9 Serial Communications Serial Bandwidth T -1 C ircu it Digital Hierarchy D S -0 chan nels 1 thro ugh 2 4 1 2 3 4 5 6 7 ………… 24 Fram ing … Inform ation 6 4 kb ps 64 k bp s 6 4 k bp s 6 4 kb ps 64 kbps 64 kbp s 64 kbps 64 k bps 6 4 kbp s 8 kb ps DS-1 Frame 1.544 Mb/s  ------------------------------------------------------------ D S -1 Fram e (1.544 M bp s) ----------- --------------------------------------------------- TDM (Time Division Multiplexing) is a communication process that transmits multiple digital signals (channels) over a common medium. T-1 (or really DS-1) is part of a hierarchy of standards known as the Digital Services Hierarchy. The term T-1 was originated by the phone company as a specific type of equipment. The term DS-1 refers to the actual signaling rate of 1.544Mbps. – 8 bits per channel x 8,000 channels per second = 64,000 bps Over the years the term T-1 has generally become synonymous with DS-1. H.Swaih 10 5  7/9/2024 N o r th A m e r ic a D S H ie r a r c h y D ig ita l D a ta R a te N um ber of C o r r e s p o n d in g S e r v ic e s D S -0 ’s T r a n s m is s io n S e r v ic e D S -0 64 kbps 1 D S - 0 o r s w itc h e d 6 4 K D S -1 1.5 4 4 M b p s 24 T -1 D S -2 3.1 5 2 M b p s 96 T -2 D S -3 4 4.7 3 6 M b p s 672 T -3 D S -4 2 7 4.1 7 6 M b p s 4 ,0 3 2 T -4 S O N E T ’s O C (O p tic a l C a r r ie r S ta n d a r d s ) Standards D ig ita l S e r v ic e T r a n s m is s io n R a te L evel  North American (T-carrier) specification O C -1 5 1.8 4 0 M b p s O C -3 1 5 5.5 2 M b p s  European (E-carrier) system O C -1 2 6 2 2.0 8 M b p s O C -2 4 1.2 4 4 G b p s  U.S. Optical Carrier (OC) bandwidth points O C -3 6 1.8 6 6 G b p s O C -4 8 2.4 8 8 G b p s OC transmission are standardized transmission for digital O C –192 9.6 G b p s signals carried on SONET fiber-optic networks. C C I T T D ig it a l H ie r a r c h y - I n te r n a tio n a l S ta n d a r d s D ig ita l D a ta R a te N um ber of C o r r e s p o n d in g S e r v ic e s c h a n n e ls T r a n s m is s io n S e r v ic e 1 2.0 4 8 M b p s 30 E -1 2 8.4 4 8 M b p s 120 E -2 3 3 4.3 6 8 M b p s 480 E -3 4 1 3 9.2 6 4 M b p s 1 ,9 2 0 E -4 5 5 6 5.1 4 8 M b p s 7 ,6 8 H.Swaih 0 E -5 11 HDLC Encapsulation WAN Encapsulation Protocols Layer 2 WAN Protocols HDLC (High-Level Data Link Control) - Default Synchronous circuit encapsulation 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- Asynchronous circut network Has built-in security mechanisms such as PAP and CHAP In terms of data transmission, synchronous ("with time" - a common timing signal is used Serial Line Internet Protocol (SLIP) - Displaced by PPP between hosts) and asynchronous ("without respect to time" - no clock or timing source is needed - PSTN). H.Swaih 12 6  7/9/2024 HDLC Encapsulation WAN Encapsulation Protocols Synchronous Data Transmission: In synchronous transmission, a common timing signal or clock is shared between the communicating hosts. This shared clock allows the data to be transmitted and received in a synchronized manner, "in time" with the clock. Synchronous transmission is commonly used for dedicated leased lines, ISDN, and other WAN links that provide a dedicated timing source. Synchronous protocols like Cisco HDLC and frame relay rely on this shared timing to ensure reliable, high-speed data transfer. Asynchronous Data Transmission: Asynchronous transmission does not require a shared clock or timing signal between the hosts. Each host transmits data independently, without any specific timing requirements. This makes asynchronous transmission well-suited for dial-up connections, like those used in the public switched telephone network (PSTN). Asynchronous protocols like the original serial PPP implementation are designed to work without any common timing source between the endpoints. Key Differences: Synchronous transmission is generally faster and more efficient Asynchronous transmission is more flexible, as it does not require a dedicated timing source, making it better suited for dial-up and lower-speed connections. PPP can operate in both synchronous and asynchronous modes, providing flexibility to work with different WAN link types and requirements. H.Swaih 13 HDLC Encapsulation Legacy Layer 2 WAN Protocols WAN Encapsulation Protocols X.25/Link Access Procedure, Balanced (LAPB) - Predecessor to Frame Relay. – Within the X.25 protocol suite, the data link layer protocol used is called LAPB (Link Access Procedure, Balanced). Frame Relay - Data link layer protocol that handles multiple virtual circuits. After X.25 ATM - International standard for cell relay in which devices send multiple Serial Serial service types, such as voice, video, or data, in fixed-length (53-byte) cells. Takes advantage of high-speed transmission media such as E3, Replaced by other Packet Switching technologies such as MPLS SONET, and T3.. H.Swaih 14 7  7/9/2024 HDLC Encapsulation  HDLC is a synchronous data link layer HDLC Encapsulation protocol developed by the International Organization for Standardization (ISO). Standard HDLC to Cisco HDLC.  Defines a Layer 2 framing structure  Default serial encapsulation on Cisco routers.  Protocol field makes it possible for a single serial link to accommodate multiple network-layer protocols. ꟷ By including the Protocol field, HDLC enables the multiplexing of multiple network protocols over a single serial link. Uses a frame delimiter, or With an added protocol type field, flag, to mark beginning and Cisco HDLC can only work with ꟷ The receiver can then demultiplex end of each frame. other Cisco devices. the incoming frames based on the Protocol field value and pass them to the appropriate network-layer H.Swaih protocol stack. 15 HDLC Encapsulation Configuring HDLC Encapsulation  Use Cisco HDLC as a point-to-point protocol on leased lines between two Cisco devices.  If connecting non-Cisco devices, use synchronous PPP.  If the default encapsulation method has been changed, use the encapsulation hdlc command in interface R1 configuration mode to re-enable HDLC. R2 R1(config)# interface serial 0/0/0 R1(config-if)# encapsulation hdlc R2(config)# interface serial 0/0/0 R2(config-if)# encapsulation hdlc H.Swaih 16 8  7/9/2024 HDLC Encapsulation Troubleshooting a Serial Interface  The show interfaces serial x/x/x command displays information specific to serial interfaces.  When HDLC is configured, “encapsulation HDLC” should be reflected in the output as highlighted in the figure.  “Serial 0/0/0 is up, line protocol is up”, indicates that the line is up and functioning. H.Swaih 17 HDLC Encapsulation Troubleshooting a Serial Interface (Cont.) Serial interface issues associated with state, and how to troubleshoot the issue. H.Swaih 18 9  7/9/2024 HDLC Encapsulation Troubleshooting a Serial Interface (Cont.) Show controllers command output indicates the state of the interface channels and whether a cable is attached to the interface – In the figure, interface serial 0/0/0 has a V.35 DCE cable attached. “UNKNOWN” instead of “V.35”, “EIA/TIA-449”, or some other electrical interface type, the likely problem is an improperly connected cable. H.Swaih 19 PPP Operations: LCP and NCP H.Swaih 20 10  7/9/2024 Benefits of PPP Introducing PPP PPP encapsulates data frames for transmission over Layer 2 physical links. PPP establishes a direct connection using a variety of physical media and communication links, including: serial cables, phone lines, trunk lines, cellular telephones, specialized radio links, or fiber-optic links. H.Swaih 21 Benefits of PPP Introducing PPP PPP contains three main components: – HDLC-like framing for transporting multiprotocol packets over point-to-point links. – Network Control Protocols (NCPs) for establishing and configuring different network layer protocols (IPv4 and IPv6 Control Protocol). – Extensible Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection. H.Swaih 22 11  7/9/2024 Benefits of PPP Advantages of PPP PPP includes many features not available in HDLC: – The link quality management feature (LQM) monitors the quality of the link. If the error percentage falls below the configured threshold, – Link is taken down – Packets are rerouted or dropped. – PPP supports authentication with: PAP (Password Authentication Protocol) CHAP (Challenge Handshake Authentication Protocol) H.Swaih 23 LCP and NCP PPP Layered Architecture The figure maps the layered architecture of PPP against the Open System Interconnection (OSI) model. PPP and OSI share the same physical layer, but PPP distributes the functions of LCP and NCP differently. PPP requires a full-duplex circuit, either dedicated or switched, that can operate in an asynchronous or synchronous bit-serial mode. Most of the work done by PPP happens at the data link and network layers, by LCP and NCPs. H.Swaih 24 12  7/9/2024 LCP and NCP PPP – Link Control Protocol (LCP) PPP defines the Link Control Protocol (LCP). The job of the LCP is to establish, configure, and test the data-link connection. In other words, LCP is responsible for negotiating and establishing the initial PPP connection between the link partners. – Handling varying limits on packet size: 1500 byte LCP allows the link partners to negotiate the maximum transmission unit (MTU) size that can be supported over the link. – Detecting common misconfiguration errors: LCP can identify and report configuration errors that may occur during the negotiation process. – Terminating the link: LCP provides mechanisms to gracefully terminate the PPP connection when needed. – Determining when a link is functioning properly or when it is failing: LCP monitors the status of the link and can detect when the connection is experiencing issues. H.Swaih 25 LCP and NCP PPP – Link Control Protocol (LCP) These packets (LCP packets) allow link partners to dynamically negotiate link options: – Authentication: LCP supports authentication protocols like PAP and CHAP to verify the identities of the link partners. – Compression (Stacker or Predictor): LCP can negotiate the use of data compression algorithms, such as Stacker or Predictor, to optimize bandwidth utilization. – Multilink PPP: LCP enables the use of Multilink PPP, which allows the aggregation of multiple physical links into a single logical link. – Callback: LCP supports the callback feature, where one link partner can request the other to initiate a callback connection. H.Swaih 26 13  7/9/2024 LCP and NCP PPP – Network Control Protocol (NCP) Once the LCP establishes the Layer 2 connection, the Network Control Protocol (NCP) takes over. Link partners exchange NCP packets to establish and configure different network-layer protocols including IPv4 or IPv6 – PPP permits multiple network layer protocols to operate on the same communications link. Each Layer 3 protocol has its own NCP, as shown in the figure. IPv4 uses IP Control Protocol and IPv6 uses IPv6 Control Protocol. NCPs include functional fields containing standardized codes to indicate the network layer protocol that PPP encapsulates. – Value 0x8021 = IPCP – Value 0x8057 = IPv6CP – Value 0x8033 - Password Authentication Protocol (PAP) – Value 0xC023 - Challenge Handshake Authentication Protocol (CHAP) When a host requests that the connection be terminated: – NCP tears down the Layer 3 sessions – Then the LCP tears down the data link H.Swaih 27 H.Swaih 28 14  7/9/2024 LCP and NCP PPP Frame Structure size byte PPP Frame Fields Flag - A single byte that indicates the beginning or end of a frame. The Flag field consists of the binary sequence 01111110. Address - A single byte that contains the binary sequence 11111111, the standard broadcast address Control - A single byte that contains the binary sequence 00000011, which calls for transmission of user data in an unsequenced frame. Protocol - Two bytes that identify the protocol encapsulated in the data field of the frame. Data - Zero or more bytes that contain the datagram for the protocol specified in the protocol field. Frame Check Sequence (FCS) – This is normally 16 bits (2 bytes). If the receiver’s calculation of the FCS does not match the FCS in the PPP frame, the PPP frame is silently discarded H.Swaih 29 PPP Sessions Establishing a PPP Session Phase 1: Link establishment and configuration negotiation - Before PPP exchanges any network layer datagrams, such as IP, the LCP must first open the connection and negotiate configuration options. Phase 2: Link quality determination (optional) - The LCP tests the link to determine whether the link quality is sufficient to bring up network layer protocols. – This may involve running various tests and measurements to evaluate the link's characteristics, such as error rates, throughput, and reliability. – If the link quality is deemed insufficient, the PPP session may be terminated or the negotiation may be retried with different configuration options. Phase 3: Network layer protocol configuration negotiation - NCP can separately configure the network layer protocols, and bring them up and take them down at any time. H.Swaih 30 15  7/9/2024 PPP Sessions LCP Operation Link Establishment LCP operation includes provisions for 3 classes of LCP frames: – Link-establishment frames establish and configure a link (Configure- Request, Configure-Ack, Configure- Nak, and Configure-Reject). Responder processes the request: – Link-maintenance frames manage Options not acceptable or not recognized: Responder and debug a link (Code-Reject, sends Configure-Nak or Configure-Reject message. Protocol Reject, Echo-Request, Echo- Reply, and Discard-Request). Options are acceptable: Responder sends with a – Link-termination frames terminate Configure-Ack message a link (Terminate-Request and ꟷ Goes to the authentication stage. Terminate-Ack). ꟷ The operation of the link is handed over to the NCP. Link establishment - LCP opens the ꟷ When NCP has completed all necessary configurations, connection and negotiates the configuration parameters. including validating authentication, the line is available for data transfer. During the exchange of data, LCP Initiating device sends Configure- Request frame. transitions into link maintenance. H.Swaih 31 PPP Sessions LCP Operation (Cont.) During link maintenance, LCP can use messages to provide feedback and test the link. – Echo-Request, Echo-Reply, and Discard-Request - These frames can be used for testing the link. – Code-Reject and Protocol-Reject - These frame types provide feedback when one device receives an invalid frame. The sending device will resend the packet. Link Maintenance H.Swaih 32 16  7/9/2024 PPP Sessions LCP Operation (Cont.) Link Termination – After the transfer of data at the network layer completes, the LCP terminates the link. – NCP only terminates the network layer and NCP link. The link remains open until the LCP terminates it. PPP terminates the link because of – loss of the carrier – authentication failure – link quality failure – expiration of an idle-period timer Device initiating the shutdown sends a Terminate- – administrative closing of the link Request message. Other device replies with a The LCP closes the link by exchanging Terminate-Ack. H.Swaih 33 Terminate packets. PPP Sessions PPP Configuration Options  Authentication using either PAP or CHAP  Compression using either Stacker or Predictor  Multilink that combines two or more channels to increase the WAN bandwidth H.Swaih 34 17  7/9/2024 PPP Sessions NCP Explained After LCP has established the link, the routers exchange IPCP messages, negotiating options specific to IPv4. IPCP (IPv6CP) is responsible for configuring, enabling, and disabling the IP modules on both ends of the link. IPCP (IPv6CP) negotiates two options: Compression - devices to negotiate an algorithm to compress TCP and IP headers. IP-Address - initiating device specifies an IP address to use for routing IP over the PPP link, or to request an IP address for the responder. After the NCP process is complete, the link goes into the open state and LCP takes over again in a H.Swaih link maintenance phase. 35 PPP Implementation (Configuring PPP Encapsulation) H.Swaih 36 18  7/9/2024 Configure PPP PPP Configuration Options  Authentication – Two authentication choices are Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP).  Compression – Increases the effective throughput on PPP connections by reducing the amount of data in the frame that must travel across the link. The protocol decompresses the frame at its destination. Two compression protocols available in Cisco routers are Stacker and Predictor.  Error detection – Identifies fault conditions. The Quality and Magic Number options help ensure a reliable, loop-free data link. The Magic Number field helps in detecting links that are in a looped-back condition. Magic numbers are generated randomly at each end of the connection. Configure PPP PPP Configuration Options  PPP Callback – PPP callback is used to enhance security. With this LCP option, a Cisco router can act as a callback client or a callback server. The client makes the initial call, requests that the server call it back, and terminates its initial call. The callback router answers the initial call and makes the return call to the client based on its configuration statements.  Multilink – This alternative provides load balancing over the router interfaces that PPP uses. Multilink PPP provides a method for spreading traffic across multiple physical WAN links while providing packet fragmentation and reassembly, proper sequencing, multivendor interoperability, and load balancing on inbound and outbound traffic. 19  7/9/2024 Configure PPP PPP Basic Configuration Command  Remember that if PPP is not configured on a Cisco router, the default encapsulation for serial interfaces is HDLC.  PPP is a Layer 2 encapsulation that supports various Layer 3 protocols including IPv4 and IPv6. R1 R2 R1(config)# interface serial 0/0/0 R1(config-if)# ip add 10.0.1.1 255.255.255.252 R1(config-if)# ipv6 add 2001:db8:cafe:1::1/64 R1(config-if)# encapsulation ppp R2(config)# interface serial 0/0/0 R2(config-if)# ip add 10.0.1.2 255.255.255.252 R2(config-if)# ipv6 add 2001:db8:cafe:1::2/64 R2(config-if)# encapsulation ppp H.Swaih 39 Configure PPP PPP Link Quality Monitoring Command  The ppp quality percentage command ensures that the link meets the set quality requirement; otherwise, the link closes down R1 R2  The percentages are calculated for both incoming and outgoing directions.  The outgoing quality is calculated by comparing the total number of packets and bytes sent, to 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 to the total number of packets and bytes sent by the destination node. H.Swaih 40 20  7/9/2024 Configure PPP PPP Link Quality Monitoring Command  Configuration ppp quality 80, as shown in the below, sets minimum quality to 80% R1 R2 R1(config)# interface serial 0/0/0 R1(config-if)# ip add 10.0.1.1 255.255.255.252 R1(config-if)# ipv6 add 2001:db8:cafe:1::1/64 R1(config-if)# encapsulation ppp R1(config-if)# ppp quality 80 LQM maintains a count of the number R2(config)# interface serial 0/0/0 of packets and octets transmitted and R2(config-if)# ip add 10.0.1.2 255.255.255.252 successfully received, and periodically R2(config-if)# ipv6 add 2001:db8:cafe:1::2/64 transmits this information to its peer R2(config-if)# encapsulation ppp in a Link Quality Report packet. R2(config-if)# ppp quality 80 H.Swaih 41 Configure PPP PPP Compression Commands  Point-to-point software compression on serial interfaces can be configured after PPP encapsulation is enabled.  Because this option invokes a software compression process, R1 it can affect system performance. If the traffic R2 already consists of compressed files, such as.zip,.tar, or.mpeg, do not use this option. PPP compress Command *LZS: Lempel Ziv-Stac H.Swaih 42 21  7/9/2024 Configure PPP PPP Compression Commands R1(config)# interface serial 0/0/0 R1(config-if)# ip add 10.0.1.1 255.255.255.252 R1 R2 R1(config-if)# ipv6 add 2001:db8:cafe:1::1/64 R1(config-if)# encapsulation ppp R1(config-if)# compress { predictor | stacker } R2(config)# interface serial 0/0/0 R2(config-if)# ip add 10.0.1.2 255.255.255.252 R2(config-if)# ipv6 add 2001:db8:cafe:1::2/64 R2(config-if)# encapsulation ppp R1(config-if)# compress { predictor | stacker } H.Swaih 43 Configure PPP PPP Multilink Commands  Multilink PPP provides a method for spreading traffic across multiple physical WAN links.  Configuring MPPP requires two steps: Step 1. Create a multilink bundle. ꟷ Use the interface multilink number global configuration command to create the multilink interface. ꟷ In interface configuration mode, assign an IPv4 and/or IPv6 address to the multilink interface. ꟷ Use the ppp multilink interface configuration command to enable multilink PPP. ꟷ Use the ppp multilink group number interface configuration command to assign the multilink group number. Step 2. Assign each physical interface to the multilink bundle. ꟷ Use the ppp encapsulation interface configuration command to enable PPP. ꟷ Use the ppp multilink interface configuration command to enable multilink PPP. ꟷ Use the ppp multilink group number interface configuration command to assign the multilink group number. H.Swaih 44 22  7/9/2024 Configure PPP PPP Multilink Commands  To disable PPP multilink, use the no ppp multilink command on each of the bundled interfaces.  Multilink PPP (also referred to as MP, MPPP, MLP, or Multilink) provides a method  for spreading traffic across multiple physical WAN links.  MPPP allows packets to be fragmented and sends these fragments simultaneously  over multiple point-to-point links to the same remote address. H.Swaih 45 Configure PPP PPP Multilink Commands R3 and R4 PPP Multilink Configuration R3(config)# interface Multilink 1 R4(config)# interface Multilink 1 R3(config-if)# ip address 10.0.1.1 R4(config-if)# ip address 10.0.1.2 255.255.255.252 255.255.255.252 R3(config-if)# ipv6 address R4(config-if)# ipv6 address 2001:db8:cafe:1::1/64 2001:db8:cafe:1::2/64 R3(config-if)# ppp multilink R4(config-if)# ppp multilink R3(config-if)# ppp multilink group 1 R4(config-if)# ppp multilink group 1 R3(config-if)# interface Serial 0/1/0 R4(config-if)# interface Serial 0/0/0 R3(config-if)# no ip address R4(config-if)# no ip address R3(config-if)# encapsulation ppp R4(config-if)# encapsulation ppp R3(config-if)# ppp multilink R4(config-if)# ppp multilink R3(config-if)# ppp multilink group 1 R4(config-if)# ppp multilink group 1 R3(config-if)# interface Serial 0/1/1 R4(config-if)# interface Serial 0/0/1 R3(config-if)# no ip address R4(config-if)# no ip address R3(config-if)# encapsulation ppp R4(config-if)# encapsulation ppp R3(config-if)# ppp multilink R4(config-if)# ppp multilink R3(config-if)# ppp multilink group 1 R4(config-if)# ppp multilink group 1 46 H.Swaih 23  7/9/2024 Configure PPP Verifying PPP Configuration Verifying the Serial PPP Encapsulation Configuration R2# show interfaces serial 0/0/0  Use the show interfaces Serial0/0/0 is up, line protocol is up serial command to verify Hardware is GT96K Serial the proper configuration Internet address is 10.0.1.2/30 of HDLC or PPP MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec, encapsulation. The reliability 255/255, txload 1/255, rxload 1/255 Encapsulation PPP, LCP Open command output in Open: IPCP, IPV6CP, CCP, CDPCP, loopback not set Figure shows a PPP Keepalive set (10 sec) configuration. CRC checking enabled Last input 00:00:02, output 00:00:02, output hang never Last clearing of "show interface" counters 01:29:06 Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 …… omitted …… R2# H.Swaih 47 Configure PPP Verifying PPP Configuration Verifying PPP Multilink Configuration R3# show ppp multilink The show interfaces Multilink1 command displays statistics Bundle name: R4 for all interfaces configured Remote Endpoint Discriminator: R4 on the router Any Name Local Endpoint Discriminator: R3 The show ppp multilink Bundle up for 00:01:20, total bandwidth 3088, load 1/255 command verifies that PPP Receive buffer limit 24000 bytes, frag timeout 1000 ms multilink is enabled on R3, as shown in the figure. The 0/0 fragments/bytes in reassembly list output indicates the 0 lost fragments, 0 reordered interface Multilink 1, the 0/0 discarded fragments/bytes, 0 lost received hostnames of both the local 0x2 received sequence, 0x2 sent sequence and remote endpoints, and Member links: 2 active, 0 inactive (max 255, min not set) the serial interfaces Se0/1/1, since 00:01:20 assigned to the multilink Se0/1/0, since 00:01:06 bundle. No inactive multilink interfaces R3# H.Swaih 48 24  7/9/2024 Configure PPP Authentication PPP Authentication Protocols  PAP is a very basic two-way process with no encryption.  The username and password are sent in plaintext. If it is accepted, the connection is allowed.  CHAP is more secure than PAP.  It involves a three-way exchange of a shared secret.  The authentication phase of a PPP session is optional.  After LCP establishes the link and chooses the authentication protocol.  Before the network layer protocol (NCP) configuration phase. H.Swaih 49 Configure PPP Authentication Password Authentication Protocol (PAP) Initiating PAP – R1 Sends its PAP username and password to R3. Note: PAP is not a strong authentication Completing PAP – R3 Evaluates R1’s username protocol. Using PAP, passwords are sent across and password against its local database. the link in plaintext and there is no protection If it matches, it accepts the connection. from playback or repeated trial-and-error If not, it rejects the connection. attacks. H.Swaih 50 25  7/9/2024 Configure PPP Authentication Password Authentication Protocol (PAP) PAP may be used in the following environments:  A large installed base of client applications that do not support CHAP  Incompatibilities between different vendor implementations of CHAP  Situations in which a plaintext password must be available to simulate a login at the remote host H.Swaih 51 Configure PPP Authentication Challenge Handshake Authentication Protocol (CHAP) #1 R3 initiates the 3-way handshake and sends a challenge message to R1. #3 The local router checks the response against its own calculation of the expected hash value. If the values match, the initiating node acknowledges the authentication. #2 The remote node responds with a value that is calculated using a one-way Note: CHAP provides protection against a playback attack by using a variable challenge value that is unique and hash function. This is typically Message unpredictable. CHAP conducts periodic challenges to make Digest 5 (MD5) based on the password sure that the remote node still has a valid password value. and challenge message H.Swaih 52 26  7/9/2024 Configure PPP Authentication PPP Authentication Command  To specify the order in which the CHAP or PAP protocols are requested on the interface, use the ppp authentication interface configuration command. Use the no form of the command to disable this authentication.  PAP, CHAP, or both can be enabled. If both methods are enabled, the first method specified is requested during link negotiation. If the peer suggests using the second method or simply refuses the first method, the second method should be tried. H.Swaih 53 Configuring PAP DTE 172.25.3.0/24 DCE.2/S0 Serial.1/S0 hostname SantaCruz hostname HQ username HQ password HQpass username SantaCruz password SantaCruzpass interface Serial0 interface Serial0 ip address 172.25.3.2 255.255.255.0 ip address 172.25.3.1 255.255.255.0 encapsulation ppp encapsulation ppp must ppp authentication pap ppp authentication pap ppp pap sent-username SantaCruz ppp pap sent-username HQ password SantaCruzpass password HQpass H.Swaih 54 27  7/9/2024 1 PAP PPP establish link 2 Configuration Request: PAP 3 4 Configuration ACK SantaCruz looks up sent- username and password for this interface: sent-username SantaCruz and 6 5 password SantaCruzpass HQ looks up username SantaCruz ppp pap sent-username and retrieves the password: SantaCruz password Yes, generate ACK username SantaCruz password SantaCruzpass message. SantaCruzpass Same? No, generate NACK message. H.Swaih 55 Configuring CHAP DTE 172.25.3.0/24 DCE.2/S0 Serial.1/S0 hostname SantaCruz hostname HQ username HQ password boardwalk username SantaCruz password boardwalk interface Serial0 interface Serial0 ip address 172.25.3.2 255.255.255.0 ip address 172.25.3.1 255.255.255.0 encapsulation ppp encapsulation ppp ppp authentication chap ppp authentication chap Same shared password H.Swaih 56 28  7/9/2024 1 CHAP SantaCruz initiates call 2 3 Challenge labeled from HQ SantaCruz looks up username HQ (authentication name) and retrieves the password: username HQ password boardwalk 4 MD5 Hash Hash Value sent with 6 5 authentication name SantaCruz Password fed HQ looks up username SantaCruz Hash Value and retrieves the password: into MD5 Hash and generates a username SantaCruz password Hash value boardwalk Password fed Yes, generate SUCCESS MD5 Hash into MD5 Hash message. Same? and generates a Hash Value Hash value No, generate FAILURE message. H.Swaih 57 Troubleshoot WAN Connectivity H.Swaih 58 29  7/9/2024 Troubleshooting PPP Serial Encapsulation  debug command must not be used as a monitoring tool  meant to be used for a short period of time for troubleshooting  can consume a significant amount of resources  MPPC (Microsoft Point-to-Point Compression) H.Swaih 59 Troubleshoot PPP Debug PPP Use the debug ppp negotiation command to verify PPP negotiation. Four possible points of failure in PPP negotiation: – No response from the remote device. – Link Control Protocol (LCP) not open. – Authentication failure. – IP Control Protocol (IPCP) failure. H.Swaih 60 30  7/9/2024 Troubleshoot PPP Debug PPP Verify that the CHAP username and password are correct using debug ppp negotiation command. H.Swaih 61 Troubleshoot PPP Troubleshooting a PPP Configuration with Authentication  In the last line, the code 4 means that a failure has occurred.  Other code values are as follows:  1 – Challenge 2 – Response 3 – Success 4 – Failure  The last line also displays the ID number of the LCP packet (that is, id – 3) and its packet length (that is, len – 48) without H.Swaih 62 the header. 31