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E4_3 PPP

John Dedios CCNA CCNA Spanish 90 cards

E4_3 PPP

Cards in this deck (90)

  1. 1PPP Is a protocol that is able to handle authentication, compression, error detection, monitor link quality, and logically bundles multiple serial connections together to share the load.One of the most common types of WAN connections, especially in long-distance communications, is a point-to-point connection, also called a serial or leased-line connection.
  2. 2Serial and Parallel Ports Point-to-point connections are used to connect LANs to service provider WANs, and to connect LAN segments within an enterprise network. Are dedicated for use by the company leasing the lines. Companies pay for a continuous connection between two remote sites, and the line is continuously active and available. and they are generally priced based on the bandwidth required and the distance between the two connected points. RS-232 --> USBSerial and Parallel Ports Point-to-point connections are used to connect LANs to service provider WANs, and to connect LAN segments withi...
  3. 3Serial and Parallel Ports Communications across a serial connection is a method of data transmissions in which the bits are transmitted sequentially over a single channel. This is equivalent to a pipe only wide enough to fit one ball at a time. Multiple balls can only go into the pipe, but only one at a time, and they only have one exit point, the other end of the pipe. A serial port is bidirectional, and often referred to as a bidirectional port or a communications port.This is in contrast to parallel communications in which bits can be transmitted simultaneously over multiple wires.
    However, parallel communications do have issues with crosstalk across wires, especially as the wire length increases.
    ** Clock skew occurs when data across the various wires does not arrive at the same time, creating synchronization issues. Finally, most parallel communications supports only one-direction, outbound-only communication from the hard drive.
  4. 4Serial Communication * RS-232 - Most serial ports on personal computers conform to the RS-232C or newer RS-422 and RS-423 standards. Both 9-pin and 25-pin connectors are used, many network devices use RJ-45 connectors that conform to the original RS-232 standard. * V.35 - Typically used for modem-to-multiplexer communication, this ITU standard for high-speed, synchronous data exchange combines the bandwidth of several telephone circuits. In the U.S., V.35 is the interface standard used by most routers and DSUs that connect to T1 carriers.V.35 cables are high-speed serial assemblies designed to support higher data rates and connectivity between DTEs and DCEs over digital lines.
    * HSSI - A High-Speed Serial Interface (HSSI) supports transmission rates up to 52 Mb/s. Engineers use HSSI to connect routers on LANs with WANs over high-speed lines, such as T3 lines.
    Engineers also use HSSI to provide high-speed connectivity between LANs, using Token Ring or Ethernet. HSSI is a DTE/DCE interface developed by Cisco Systems and T3 plus Networking to address the need for high-speed communication over WAN links.
  5. 5Time-Division Multiplexing Multiplexing refers to a scheme that allows multiple logical signals to share a single physical channel. Two common types of multiplexing are time-division multiplexing (TDM) and statistical time-division multiplexing (STDM). ** TDM is a physical layer concept. It has no regard for the nature of the information that is multiplexed on to the output channel. TDM is independent of the Layer 2 protocol that has been used by the input channels. ** T1/E1 and ISDN telephone lines are common examples of synchronous TDM.Time-Division Multiplexing Multiplexing refers to a scheme that allows multiple logical signals to share a single physical channel. Two c...
  6. 6Time-Division Multiplexing TDM divides the bandwidth of a single link into separate time slots. TDM transmits two or more channels (data stream) over the same link by allocating a different time slot for the transmission of each channel. In effect, the channels take turns using the link. TDM allows the transmission of multiple streams of data across a link by dividing transmission time into smaller, equal intervals so that the link carries the bits from multiple input sources. A multiplexer (MUX) at the transmitter accepts three separate signals. The MUX breaks each signal into segments. The MUX puts each segment into a single channel by inserting each segment into a time slot.A MUX at the receiving end reassembles the TDM stream into the three separate data streams based only on the timing of the arrival of each bit.
    A technique called bit interleaving keeps track of the number and sequence of the bits from each specific transmission so that they can be quickly and efficiently reassembled into their original form upon receipt.
    Byte interleaving performs the same functions, but because there are eight bits in each byte, the process needs a bigger or longer time slot.
  7. 7Time-Division Multiplexing TDM can be explained by an analogy to highway traffic. To transport traffic from four roads to another city, all traffic can be sent on one lane if the roads are equally serviced and the traffic is synchronizedIf each of the four roads puts a car on to the main highway every four seconds, the highway gets a car at the rate of one each second. As long as the speed of all the cars is synchronized, there is no collision.
    At the destination, the reverse happens and the cars are taken off the highway and fed to the local roads by the same synchronous mechanism.
  8. 8Time-Division Multiplexing In another analogy, compare TDM to a train with 32 railroad cars. Each car is owned by a different freight company, and every day the train leaves with the 32 cars attached. If one of the companies has cargo to send, the car is loaded.** If the company has nothing to send, the car remains empty, but stays on the train.
    Shipping empty containers is not very efficient. TDM shares this inefficiency when traffic is intermittent, because the time slot is still allocated even when the channel has no data to transmit.
  9. 9Statistical Time-Division Multiplexing STDM was developed to overcome this inefficiency. (Train Analogy) 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. STDM requires each transmission to carry identification information or a channel identifier.Statistical Time-Division Multiplexing STDM was developed to overcome this inefficiency. (Train Analogy) STDM uses a variable time slot l...
  10. 10STDM Example- Synchronous Optical Networking (SONET) or Synchronous Digital Hierarchy (SDH) SONET, used in North America, and SDH, used elsewhere Ej: SONET/SDH takes n bit streams, multiplexes them, and optically modulates the signals. It then sends the signals out using a light emitting device over fiber with a bit rate equal to (incoming bit rate) x n. Thus, traffic arriving at the SONET multiplexer from four places at 2.5 Gb/s goes out as a single stream at 4 x 2.5 Gb/s, or 10 Gb/s.STDM Example- Synchronous Optical Networking (SONET) or Synchronous Digital Hierarchy (SDH) SONET, used in North America, and SDH, used e...
  11. 11Demarcation Point In the United States, a service provider provides the local loop into the customer premises, and the customer provides the active equipment such as the CSU/DSU on which the local loop is terminated. This termination often occurs in a telecommunications closet, and the customer is responsible for maintaining, replacing, or repairing the equipment. In other countries, the network terminating unit (NTU) is provided and managed by the service provider. This allows the service provider to actively manage and troubleshoot the local loop with the demarcation point occurring after the NTU. The customer connects a CPE device, such as a router or Frame Relay access device, to the NTU using a V.35 or RS-232 serial interface.Demarcation Point In the United States, a service provider provides the local loop into the customer premises, and the customer provides ...
  12. 12Demarcation Point A router serial port is required for each leased-line connection. If the underlying network is based on the T-carrier or E-carrier technologies, the leased line connects to the network of the carrier through a CSU/DSU. The purpose of the CSU/DSU is to provide a clocking signal to the customer equipment interface from the DSU and terminate the channelized transport media of the carrier on the CSU. The CSU also provides diagnostic functions such as a loopback test. Ej: most T1 or E1 TDM interfaces on current routers include CSU/DSU capabilities. A separate CSU/DSU is not required because this functionality is embedded in the interface. IOS commands are used to configure the CSU/DSU operations.Demarcation Point A router serial port is required for each leased-line connection. If the underlying network is based on the T-carrier o...
  13. 13DTE-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 DTEDTE-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 c...
  14. 14DTE-DCE From the point of view of connecting to the WAN, 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,The Electronics Industry Association (EIA) and the International Telecommunication Union Telecommunications Standardization Sector (ITU-T) have been most active in the development of standards that allow DTEs to communicate with DCEs.
  15. 15Serial Cables Originally, the concept of DCEs and DTEs was based on two types of equipment: terminal equipment that generated or received data, and the communication equipment that only relayed data. 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
  16. 16Serial Cables The original RS-232 standard only defined the connection of DTEs with DCEs, which were modems. However, to connect two DTEs, such as two computers or two routers in a lab, a special cable called a null modem eliminates the need for a DCE. In other words, the two devices can be connected without a modem. ** A null modem is a communication method to directly connect two DTEs using a RS-232 serial cable. With a null modem connection, the transmit (Tx) and receive (Rx) lines are cross-linkedSerial Cables The original RS-232 standard only defined the connection of DTEs with DCEs, which were modems. However, to connect two DTEs...
  17. 17Serial Cables The cable for the DTE to DCE connection is a shielded serial transition cable. The router end of the shielded serial transition cable may be a DB-60 connector, which connects to the DB-60 port on a serial WAN interface card, The other end of the serial transition cable is available with the connector appropriate for the standard that is to be used. The WAN provider or the CSU/DSU usually dictates this cable type. Cisco devices support the EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA/TIA-530 serial standardsSerial Cables The cable for the DTE to DCE connection is a shielded serial transition cable. The router end of the shielded serial transi...
  18. 18Serial Cables When using a null modem, synchronous connections require a clock signal. An external device can generate the signal, or one of the DTEs can generate the clock signal. ** When a DTE and DCE are connected, the serial port on a router is the DTE end of the connection, by default, and the clock signal is typically provided by a CSU/DSU, or similar DCE device. However, when using a null modem cable in a router-to-router connection, one of the serial interfaces must be configured as the DCE end to provide the clock signal for the connection,Serial Cables When using a null modem, synchronous connections require a clock signal. An external device can generate the signal, or one...
  19. 19Serial Bandwidth The underlying carrier technology depends on the bandwidth available. There is a difference in bandwidth points between the North American (T-carrier) specification and the European (E-carrier) system. Optical networks also use a different bandwidth hierarchy, which again differs between North America and Europe. In the U.S., Optical Carrier (OC) defines the bandwidth points.In North America, the bandwidth is usually expressed as a digital signal level number (DS0, DS1, etc.), which refers to the rate and format of the signal. The most fundamental line speed is 64 kb/s, or DS-0, which is the bandwidth required for an uncompressed, digitized phone call.
    Serial connection bandwidths can be incrementally increased to accommodate the need for faster transmission. For example, 24 DS0s can be bundled to get a DS1 line (also called a T1 line) with a speed of 1.544 Mb/s
    Also, 28 DS1s can be bundled to get a DS3 line (also called a T3 line) with a speed of 44.736 Mb/s
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  21. 21WAN Encapsulation Protocols On each WAN connection, data is encapsulated into frames before crossing the WAN link. To ensure that the correct protocol is used, the appropriate Layer 2 encapsulation type must be configured. ** The choice of protocol depends on the WAN technology and the communicating equipmentWAN Encapsulation Protocols On each WAN connection, data is encapsulated into frames before crossing the WAN link. To ensure that the cor...
  22. 22WAN Encapsulation Protocols 1. 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. 2. PPP - Provides router-to-router and host-to-network connections over synchronous and asynchronous circuits.PPP works with several network layer protocols, such as IPv4 and IPv6. PPP uses the HDLC encapsulation protocol, but also has built-in security mechanisms such as PAP and CHAP.
    3. Serial Line Internet Protocol (SLIP) - A standard protocol for point-to-point serial connections using TCP/IP. SLIP has been largely displaced by PPP.
  23. 23WAN Encapsulation Protocols 4. X.25/Link Access Procedure, Balanced (LAPB) - An ITU-T standard that defines how connections between a DTE and DCE are maintained for remote terminal access and computer communications in public data networks. X.25 specifies LAPB, a data link layer protocol. X.25 is a predecessor to Frame Relay. 5. Frame Relay - An industry standard, switched, data link layer protocol that handles multiple virtual circuits. Frame Relay is a next generation protocol after X.25.Frame Relay eliminates some of the time-consuming processes (such as error correction and flow control) employed in X.25.
    6. 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. ATM takes advantage of high-speed transmission media such as E3, SONET, and T3.
  24. 24HDLC Encapsulation HDLC is a bit-oriented synchronous data link layer protocol developed by the International Organization for Standardization (ISO). The current standard for HDLC is ISO 13239. HDLC was developed from the Synchronous Data Link Control (SDLC) standard proposed in the 1970s. HDLC provides both connection-oriented and connectionless service.HDLC uses synchronous serial transmission to provide error-free communication between two points.
    HDLC defines a Layer 2 framing structure that allows for flow control and error control through the use of acknowledgments.
    Each frame has the same format, whether it is a data frame or a control frame.
  25. 25HDLC Encapsulation When frames are transmitted over synchronous or asynchronous links, those links have no mechanism to mark the beginning or end of frames. For this reason, HDLC uses a frame delimiter, or flag, to mark the beginning and the end of each frame. Cisco has developed an extension to the HLDC protocol to solve the inability to provide multiprotocol support. Although Cisco HLDC (also referred to as cHDLC) is proprietary,HDLC Encapsulation When frames are transmitted over synchronous or asynchronous links, those links have no mechanism to mark the beginnin...
  26. 26HDLC Frame Types 1. y 7. Flag - initiates and terminates error checking. The frame always starts and ends with an 8-bit flag field. The bit pattern is 01111110. Because there is a likelihood that this pattern occurs in the actual data, the sending HDLC system always inserts a 0 bit after every five consecutive 1s in the data field, so in practice the flag sequence can only occur at the frame ends. The receiving system strips out the inserted bits.When frames are transmitted consecutively, the end flag of the first frame is used as the start flag of the next frame.
    2. Address - 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.
  27. 27HDLC Frame Types 3. Control - field uses three different formats, depending on the type of HDLC frame used: a. Information (I) Frame - I-frames carry upper layer information and some control information. This frame sends and receives sequence numbers, and the poll final (P/F) bit performs flow and error control. The send sequence number refers to the number of the frame to be sent next. The receive sequence number provides the number of the frame to be received next. Both sender and receiver maintain send and receive sequence numbers. A primary station uses the P/F bit to tell the secondary whether it requires an immediate response. A secondary station uses the P/F bit to tell the primary whether the current frame is the last in its current response.HDLC Frame Types 3. Control - field uses three different formats, depending on the type of HDLC frame used: a. Information (I) Frame - I-...
  28. 28HDLC Frame Types 3. Control - field uses three different formats, depending on the type of HDLC frame used: b. 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. S-frames do not have an information field. c. Unnumbered (U) Frame - U-frames support control purposes and are not sequenced. Depending on the function of the U-frame, its control field is 1 or 2 bytes. Some U-frames have an information field.HDLC Frame Types 3. Control - field uses three different formats, depending on the type of HDLC frame used: b. Supervisory (S) Frame - S-...
  29. 29HDLC Frame Types 4. Protocol- Only used in Cisco HDLC. This field specifies the protocol type encapsulated within the frame (e.g. 0x0800 for IP). 5. Data - ontains a Path Information Unit (PIU) or Exchange Identification (XID) information.6. Frame Check Sequence (FCS)
    The FCS+ precedes the ending flag delimiter and is usually a Cyclic Redundancy Check (CRC) calculation remainder.
    The CRC calculation is redone in the receiver. If the result differs from the value in the original frame, an error is assumed.
  30. 30Configuring 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. Step 1. Enter the interface configuration mode of the serial interface. Step 2. Enter the xxx command to specify the encapsulation protocol on the interface.Configuring HDLC Encapsulation ** Use Cisco HDLC as a point-to-point protocol on leased lines between two Cisco devices. If connecting no...
  31. 31Troubleshooting a Serial Interface Ej: ? command displays information specific to serial interfaces: When HDLC is configured, encapsulation HDLC should be reflected in the output A problem with the internal wiring of the card is also possible. If the electrical interface is unknown, the corresponding display for the show interfaces serial command shows that the interface and line protocol are down.Troubleshooting a Serial Interface Ej: ? command displays information specific to serial interfaces: When HDLC is configured, encapsulati...
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  35. 35Troubleshooting a Serial Interface The show interfaces serial command returns one of six possible states: - Serial x is up, line protocol is up - Serial x is down, line protocol is down- Serial x is up, line protocol is down
    - Serial x is up, line protocol is up (looped)
    - Serial x is up, line protocol is down (disabled)
    - Serial x is administratively down, line protocol is down
  36. 36Troubleshooting a Serial Interface Ej: ? The 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. 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. If the electrical interface output displays as UNKNOWN instead of V.35, EIA/TIA-449, or some other electrical interface type, the likely problem is an improperly connected cableTroubleshooting a Serial Interface Ej: ? The output indicates the state of the interface channels and whether a cable is attached to the ...
  37. 37Introducing PPP PPP encapsulation has been carefully designed to retain compatibility with most commonly used supporting hardware. 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.Introducing PPP PPP encapsulation has been carefully designed to retain compatibility with most commonly used supporting hardware. PPP en...
  38. 38Introducing PPP PPP contains three main components: 1. HDLC-like framing for transporting multiprotocol packets over point-to-point links. 2. Extensible Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection.3. Family of Network Control Protocols (NCPs) for establishing and configuring different network layer protocols.
    PPP allows the simultaneous use of multiple network layer protocols.
    Some of the more common NCPs are Internet Protocol (IPv4) Control Protocol, IPv6 Control Protocol, AppleTalk Control Protocol, Novell IPX Control Protocol, Cisco Systems Control Protocol, SNA Control Protocol, and Compression Control Protocol.
  39. 39Advantages of PPP PPP originally emerged as an encapsulation protocol for transporting IPv4 traffic over point-to-point links. PPP provides a standard method for transporting multiprotocol packets over point-to-point links. ** There are many advantages to using PPP including the fact that it is not proprietary. PPP includes 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.
  40. 40PPP Layered Architecture ** A layered architecture is a logical model, design, or blueprint that aids in communication between interconnecting layers. ** Most of the work done by PPP is at the data link and network layers by the LCP and NCPs. The LCP sets up the PPP connection and its parameters, the NCPs handle higher layer protocol configurations, and the LCP terminates the PPP connection.PPP Layered Architecture ** A layered architecture is a logical model, design, or blueprint that aids in communication between interconne...
  41. 41PPP Layered Architecture PPP operates across any DTE/DCE interface (RS-232-C, RS-422, RS-423, or V.35). ** The only absolute requirement imposed by PPP is a full-duplex circuit, either dedicated or switched, that can operate in either an asynchronous or synchronous bit-serial mode, transparent to PPP link layer frames. PPP does not impose any restrictions regarding transmission rate other than those imposed by the particular DTE/DCE interface in use.At the physical layer, you can configure PPP on a range of interfaces, including:
    - Asynchronous serial (leased line services)
    - Synchronous serial (that use basic telephone service for modem dialup connections)
    - HSSI
    - ISDN
  42. 42PPP – Link Control Protocol (LCP) The LCP has a role in establishing, configuring, and testing the data-link connection. The LCP establishes the point-to-point link. The LCP also negotiates and sets up control options on the WAN data link, which are handled by the NCPs. After the link is established, PPP also uses the LCP to agree automatically on encapsulation formats such as authentication, compression, and error detection.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
  43. 43PPP – Network Control Protocol (NCP) For every network layer protocol used, PPP uses a separate NCPFor example, IPv4 uses the IP Control Protocol (IPCP) and IPv6 uses IPv6 Control Protocol (IPv6CP). Ej: NCPs include functional fields containing standardized codes to indicate the network layer protocol that PPP encapsulates. Each NCP manages the specific needs required by its respective network layer protocols. The various NCP components encapsulate and negotiate options for multiple network layer protocols.PPP – Network Control Protocol (NCP) For every network layer protocol used, PPP uses a separate NCPFor example, IPv4 uses the IP Control ...
  44. 44PPP Frame Structure 1. y 7. Flag - A single byte that indicates the beginning or end of a frame. The flag field consists of the binary sequence 01111110. In successive PPP frames, only a single Flag character is used. 2. Address - A single byte that contains the binary sequence 11111111, the standard broadcast address. PPP does not assign individual station addresses.PPP Frame Structure 1. y 7. Flag - A single byte that indicates the beginning or end of a frame. The flag field consists of the binary se...
  45. 45PPP Frame Structure 3. Control - A single byte that contains the binary sequence 00000011, which calls for transmission of user data in an unsequenced frame. This provides a connectionless link service that does require the establishment of data links or links stations. On a point-to-point link, the destination node does not need to be addressed. Therefore, for PPP, the Address field is set to 0xFF, the broadcast address. If both PPP peers agree to perform address and control field compression during the LCP negotiation, the Address field is not included.4. Protocol - Two bytes that identify the protocol encapsulated in the information field of the frame. The 2-byte Protocol field identifies the protocol of the PPP payload.
    If both PPP peers agree to perform protocol field compression during LCP negotiation, the Protocol field is one byte for the protocol identification in the range 0x00-00 to 0x00-FF.
  46. 46PPP Frame Structure 5. Data - Zero or more bytes that contain the datagram for the protocol specified in the protocol field. The end of the information field is found by locating the closing flag sequence and allowing 2 bytes for the FCS field. The default maximum length of the information field is 1,500 bytes. By prior agreement, consenting PPP implementations can use other values for the maximum information field length.6. Frame Check Sequence (FCS) - Normally 16 bits (2 bytes). By prior agreement, consenting PPP implementations can use a 32-bit (4-byte) FCS for improved error detection.
    If the receiver’s calculation of the FCS does not match the FCS in the PPP frame, the PPP frame is silently discarded.
  47. 47Establishing 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. This phase is complete when the receiving router sends a configuration-acknowledgment frame back to the router initiating the connection. - 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. The LCP can delay transmission of network layer protocol information until this phase is complete.Establishing a PPP Session - Phase 1: Link establishment and configuration negotiation - Before PPP exchanges any network layer datagrams...
  48. 48Establishing a PPP Session - Phase 3: Network layer protocol configuration negotiation - the appropriate NCP can separately configure the network layer protocols, and bring them up and take them down at any time. If the LCP closes the link, it informs the network layer protocols so that they can take appropriate action. The link remains configured for communications until explicit LCP or NCP frames close the link, or until some external event occurs such as an inactivity timer expiring, or an administrator intervening. The LCP can terminate the link at any time.Establishing a PPP Session - Phase 3: Network layer protocol configuration negotiation - the appropriate NCP can separately configure the...
  49. 49LCP Operation LCP operation includes provisions for link establishment, link maintenance, and link termination. LCP operation uses three classes of LCP frames to accomplish the work of each of the LCP phases: 1. Link-establishment frames establish and configure a link (Configure-Request, Configure-Ack, Configure-Nak, and Configure-Reject).2. Link-maintenance frames manage and debug a link (Code-Reject, Protocol-Reject, Echo-Request, Echo-Reply, and Discard-Request).
    3. Link-termination frames terminate a link (Terminate-Request and Terminate-Ack).
  50. 50LCP Operation 1. Link establishment is the first phase of LCP operation. This phase must complete successfully, before any network layer packets can be exchanged. During link establishment, the LCP opens the connection and negotiates the configuration parameters. The link establishment process starts with the initiating device sending a Configure-Request frame to the responder. The Configure-Request frame includes a variable number of configuration options needed to set up on the link.LCP Operation 1. Link establishment is the first phase of LCP operation. This phase must complete successfully, before any network layer ...
  51. 51LCP Operation 1. Link establishment The initiator includes the options for how it wants the link created, including protocol or authentication parameters. The responder processes the request: a. If the options are not acceptable or not recognized the responder sends a Configure-Nak or Configure-Reject message. If this occurs and the negotiation fails, the initiator must restart the process with new options.b. If the options are acceptable, the responder responds with a Configure-Ack message and the process moves on to the authentication stage. The operation of the link is handed over to the NCP.
    When NCP has completed all necessary configurations, including validating authentication if configured, the line is available for data transfer. During the exchange of data, LCP transitions into link maintenance.
  52. 52LCP Operation 2. Link Maintenance a. Echo-Request, Echo-Reply, and Discard-Request - These frames can be used for testing the link. b. Code-Reject and Protocol-Reject - These frame types provide feedback when one device receives an invalid frame due to either an unrecognized LCP code (LCP frame type) or a bad protocol identifier. For example, if an interpretable packet is received from the peer, a Code-Reject packet is sent in response. The sending device will resend the packet.LCP Operation 2. Link Maintenance a. Echo-Request, Echo-Reply, and Discard-Request - These frames can be used for testing the link. b. Co...
  53. 53LCP Operation 3. 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. If the LCP terminates the link before NCP, the NCP session is also terminated. PPP can terminate the link at any time. This might happen because of the loss of the carrier, authentication failure, link quality failure, the expiration of an idle-period timer, or the administrative closing of the link.LCP Operation 3. Link Termination After the transfer of data at the network layer completes, the LCP terminates the link, ** NCP only ter...
  54. 54LCP Packet * Code - The code field is 1 byte in length and identifies the type of LCP packet. * Identifier - The identifier field is 1 byte in length and is used to match packet requests and replies. * Length - The length field is 2 bytes in length and indicates the total length (including all fields) of the LCP packet. * Data - The data field is 0 or more bytes as indicated by the length field. The format of this field is determined by the code.LCP Packet * Code - The code field is 1 byte in length and identifies the type of LCP packet. * Identifier - The identifier field is 1 by...
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  56. 56PPP Configuration Options ** These optional functions include: - Authentication using either PAP or CHAP - Compression using either Stacker or Predictor - Multilink that combines two or more channels to increase the WAN bandwidthPPP Configuration Options ** These optional functions include: - Authentication using either PAP or CHAP - Compression using either Stack...
  57. 57PPP Configuration Options To negotiate the use of these PPP options, the LCP link-establishment frames contain option information in the data field of the LCP frame If a configuration option is not included in an LCP frame, the default value for that configuration option is assumed. This phase is complete when a configuration acknowledgment frame has been sent and received.PPP Configuration Options To negotiate the use of these PPP options, the LCP link-establishment frames contain option information in the ...
  58. 58NCP Process After the link has been initiated, the LCP passes control to the appropriate NCP. After the LCP has configured and authenticated the basic link, the appropriate NCP is invoked to complete the specific configuration of the network layer protocol being used. When the NCP has successfully configured the network layer protocol, the network protocol is in the open state on the established LCP link. At this point, PPP can carry the corresponding network layer protocol packets.After the NCP process is complete, the link goes into the open state and LCP takes over again in a link maintenance phase. Link traffic consists of any possible combination of LCP, NCP, and network layer protocol packets.
    When data transfer is complete, NCP terminates the protocol link; LCP terminates the PPP connection.
  59. 59IPCP Example As an example of how the NCP layer works, the NCP configuration of IPv4, which is the most common Layer 3 protocol, Ej: After LCP has established the link, the routers exchange IPCP messages, negotiating options specific to the IPv4 protocol. IPCP is responsible for configuring, enabling, and disabling the IPv4 modules on both ends of the link. IPV6CP is an NCP with the same responsibilities for IPv6.IPCP Example As an example of how the NCP layer works, the NCP configuration of IPv4, which is the most common Layer 3 protocol, Ej: Afte...
  60. 60IPCP negotiates two options: 1. Compression - Allows devices to negotiate an algorithm to compress TCP and IP headers and save bandwidth. The Van Jacobson TCP/IP header compression reduces the size of the TCP/IP headers to as few as 3 bytes. This can be a significant improvement on slow serial lines, particularly for interactive traffic.2. IPv4-Address - Allows the initiating device to specify an IPv4 address to use for routing IP over the PPP link, or to request an IPv4 address for the responder.
    Prior to the advent of broadband technologies such as DSL and cable modem services, dialup network links commonly used the IPv4 address option.
  61. 61Steps in the LCP Link Negotiation ProcessSteps in the LCP Link Negotiation Process
  62. 62PPP Configuration Options 1. Authentication - Peer routers exchange authentication messages. Two authentication choices are Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP). 2. 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 protocols3. 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.
    Until the Magic-Number Configuration Option has been successfully negotiated, the Magic-Number must be transmitted as zero. Magic numbers are generated randomly at each end of the connection.
  63. 63PPP Configuration Options 4. 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. "ppp callback [accept | request]"5. Multilink - This alternative provides load balancing over the router interfaces that PPP uses.
    ** Multilink PPP, also referred to as MP, MPPP, MLP, or Multilink, 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.
  64. 64—
  65. 65PPP Basic Configuration Command Ej: ? To set PPP as the encapsulation method used by a serial interface PPP is a Layer 2 encapsulation that supports various Layer 3 protocols including IPv4 and IPv6.PPP Basic Configuration Command Ej: ? To set PPP as the encapsulation method used by a serial interface PPP is a Layer 2 encapsulation th...
  66. 66PPP Compression Commands Ej: ? Because this option invokes a software compression process, it can affect system performance. If the traffic already consists of compressed files, such as .zip, .tar, or .mpeg, do not use this option.PPP Compression Commands Ej: ? Because this option invokes a software compression process, it can affect system performance. If the traff...
  67. 67PPP Link Quality Monitoring - LQM Ej: ? command ensures that the link meets the quality requirement set; otherwise,If the link quality percentage is not maintained, the link is deemed to be of poor quality and is taken down. 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.PPP Link Quality Monitoring - LQM Ej: ? command ensures that the link meets the quality requirement set; otherwise,If the link quality pe...
  68. 68PPP Multilink Commands Multilink PPP (also referred to as MP, MPPP, MLP, or Multilink) provides a method for spreading traffic across multiple physical WAN links. Multilink PPP also provides packet fragmentation and reassembly, proper sequencing, multivendor interoperability, and load balancing on inbound and outbound traffic.MPPP allows packets to be fragmented and sends these fragments simultaneously over multiple point-to-point links to the same remote address. The multiple physical links come up in response to a user-defined load threshold.
    ** MPPP can measure the load on just inbound traffic, or on just outbound traffic, but not on the combined load of both inbound and outbound traffic.
  69. 69Configuring MPPP requires two steps: Step 1. Create a multilink bundle. - The interface multilink number command creates the multilink interface. - In interface configuration mode, an IP address is assigned to the multilink interface. - The interface is enabled for multilink PPP. - The interface is assigned a multilink group number.Configuring MPPP requires two steps: Step 1. Create a multilink bundle. - The interface multilink number command creates the multilink in...
  70. 70Configuring MPPP requires two steps: Step 2. Assign interfaces to the multilink bundle. Each interface that is part of the multilink group: - Is enabled for PPP encapsulation. - Is enabled for multilink PPP. - Is bound to the multilink bundle using the multilink group number configured in Step 1.Configuring MPPP requires two steps: Step 2. Assign interfaces to the multilink bundle. Each interface that is part of the multilink grou...
  71. 71Verifying PPP Configuration Ej: ? command verifies that PPP multilink is enabled on R3 The output indicates the interface Multilink 1, the hostnames of both the local and remote endpoints, and the serial interfaces assigned to the multilink bundle.Verifying PPP Configuration Ej: ? command verifies that PPP multilink is enabled on R3 The output indicates the interface Multilink 1, th...
  72. 72PPP Authentication Protocols ** PAP is a very basic two-way process. There is 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 options require that the calling side of the link enter authentication information. This helps to ensure that the user has the permission of the network administrator to make the call.PPP Authentication Protocols ** PAP is a very basic two-way process. There is no encryption. The username and password are sent in plaint...
  73. 73Password Authentication Protocol (PAP) Initiating PAP PAP provides a simple method for a remote node to establish its identity using a two-way handshake. PAP is not interactive. When the ppp authentication pap command is used, the username and password are sent as one LCP data package, rather than the server sending a login prompt and waiting for a response, After PPP completes the link establishment phase, the remote node repeatedly sends a username-password pair across the link until the receiving node acknowledges it or terminates the connection.Completing PAP
    At the receiving node, the username-password is checked by an authentication server that either allows or denies the connection. An accept or reject message is returned to the requester
    ** PAP is not a strong authentication protocol. Using PAP, passwords are sent across the link in plaintext and there is no protection from playback or repeated trial-and-error attacks. The remote node is in control of the frequency and timing of the login attempts.
  74. 74—
  75. 75Challenge Handshake Authentication Protocol (CHAP) ** After authentication is established with PAP, it does not re-authenticate. This leaves the network vulnerable to attack. ** Unlike PAP, which only authenticates once, CHAP conducts periodic challenges to make sure that the remote node still has a valid password value. The password value is variable and changes unpredictably while the link exists.CHAP provides protection against playback attack by using a variable challenge value that is unique and unpredictable. Because the challenge is unique and random, the resulting hash value is also unique and random.
    The use of repeated challenges limits the time of exposure to any single attack. The local router or a third-party authentication server is in control of the frequency and timing of the challenges.
  76. 76—
  77. 77PPP Encapsulation and Authentication Process If the authentication failed, a CHAP failure packet is built from the following components: 04 = CHAP failure message type id = copied from the response packet "Authentication failure" or some similar text message, which is meant to be a user-readable explanationPPP Encapsulation and Authentication Process If the authentication failed, a CHAP failure packet is built from the following components: ...
  78. 78PPP Encapsulation and Authentication Process Step 1. R1 initially negotiates the link connection using LCP with router R2 and the two systems agree to use CHAP authentication during the PPP LCP negotiation. Step 2. R2 generates an ID and a random number, and sends that and its username as a CHAP challenge packet to R1. Step 3. R1 uses the username of the challenger (R2) and cross references it with its local database to find its associated password.R1 then generates a unique MD5 hash number using the R2's username, ID, random number and the shared secret password. In this example, the shared secret password is boardwalk.
    Step 4. Router R1 then sends the challenge ID, the hashed value, and its username (R1) to R2.
    Step 5. R2 generates its own hash value using the ID, the shared secret password, and the random number it originally sent to R1.
    Step 6. R2 compares its hash value with the hash value sent by R1. If the values are the same, R2 sends a link established response to R1.
  79. 79Configuring PPP Authentication * PAP authentication requires the remote device to send a name and password to be checked against a matching entry in the local username database or in the remote TACACS/TACACS+ database. * CHAP authentication sends a challenge to the remote device.The remote device must encrypt the challenge value with a shared secret and return the encrypted value and its name to the local router in a response message.
    The local router uses the name of the remote device to look up the appropriate secret in the local username or remote TACACS/TACACS+ database. It uses the looked-up secret to encrypt the original challenge and verify that the encrypted values match.
  80. 80Configuring PPP Authentication ** PAP authentication requires the remote device Either PAP or 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. Some remote devices support CHAP only and some PAP only.** Note: Authentication, authorization and accounting (AAA)/TACACS is a dedicated server used to authenticate users.
    TACACS clients send a query to a TACACS authentication server. The server can authenticate the user, authorize what the user can do, and track what the user has done.
  81. 81—
  82. 82Configuring PAP Authentication Both routers authenticate and are authenticated, so the PAP authentication commands mirror each other. The PAP username and password that each router sends must match those specified with the username name password password command of the other router. The hostname on one router must match the username the other router has configured for PPP. The passwords must also match. Specify the username and password parameters, use the following command: ppp pap sent-username (name) password (password)Configuring PAP Authentication Both routers authenticate and are authenticated, so the PAP authentication commands mirror each other. The...
  83. 83Configuring CHAP Authentication CHAP periodically verifies the identity of the remote node using a three-way handshake. The hostname on one router must match the username the other router has configured. The passwords must also match. This occurs on initial link establishment and can be repeated any time after the link has been established.Configuring CHAP Authentication CHAP periodically verifies the identity of the remote node using a three-way handshake. The hostname on o...
  84. 84Troubleshooting PPP Serial Encapsulation Use the debug ppp command when trying to search the following: - NCPs that are supported on either end of a PPP connection - Any loops that might exist in a PPP internetwork - Nodes that are (or are not) properly negotiating PPP connections- Errors that have occurred over the PPP connection
    - Causes for CHAP session failures
    - Causes for PAP session failures
    - Information specific to the exchange of PPP connections using the Callback Control Protocol (CBCP), used by Microsoft clients
    - Incorrect packet sequence number information where MPPC compression is enabled
  85. 85—
  86. 86Debug PPP Ej: ? depicts packet exchanges under normal PPP operation, including LCP state, LQM procedures, and the LCP magic number.Debug PPP Ej: ? depicts packet exchanges under normal PPP operation, including LCP state, LQM procedures, and the LCP magic number.
  87. 87Debug PPP Ej: ? enables the network administrator to view the PPP negotiation transactions, identify the problem or stage when the error occurs, and develop a resolution. The output includes the LCP negotiation, authentication, and NCP negotiation.Debug PPP Ej: ? enables the network administrator to view the PPP negotiation transactions, identify the problem or stage when the error ...
  88. 88Debug PPP Ej: ? command is used to display protocol errors and error statistics associated with PPP connection negotiation and operation, These messages might appear when the Quality Protocol option is enabled on an interface that is already running PPP.Debug PPP Ej: ? command is used to display protocol errors and error statistics associated with PPP connection negotiation and operation,...
  89. 89Troubleshooting a PPP Configuration with Authentication Line 1 says that the router is unable to authenticate on interface Serial0 because the peer did not send a name. Line 2 says the router was unable to validate the CHAP response because USERNAME pioneer was not found. Line 3 says no password was found for pioneer.Troubleshooting a PPP Configuration with Authentication Line 1 says that the router is unable to authenticate on interface Serial0 becaus...
  90. 90Troubleshooting 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 id - 3 is the ID number per LCP packet format len - 48 is the packet length without the headerTroubleshooting a PPP Configuration with Authentication In the last line, the code 4 means that a failure has occurred. Other code values...

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CCNA CCNA Flashcards on E4_3 PPP, created by John Dedios on 26/08/2016.
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