CCNA2_M1_WANs_and_Routers (1130716)
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CCNA – Semester2Module 1WANs and RoutersObjectives••••WANs characteristicsDescribe the role of a router in a WANRouter componentsRouter connectionsWANsIntroduction to WANs• These are the majorcharacteristics of WANs:– They connect devices that areseparated by wide geographicalareas.– They use the services of carriers– They use serial connections ofvarious types to accessbandwidth over large geographicareas.WANs characteristics• A WAN operates at the physical layer and thedata link layer of the OSI reference model.• It interconnects LANs that are usually separatedby large geographic areas.• WANs provide for the exchange of data packetsand frames between routers and switches andthe LANs they support.WAN DevicesWAN Standards• WAN physical layer protocols describe how toprovide electrical, mechanical, operational, andfunctional connections for WAN services• WAN data link protocols describe how frames arecarried between systems on a single data link.WAN standards and OSI modelWAN SpecificationsLayersublayerMACLayerEIA/TIA-232X21 bisPhysicalSMDSsublayerEIA/TIA-449V24 V35HSSI G.703EIA-530SDLCData LinkLAPBLLCPPPLayerHDLCNetworkFrame RelayX25 PLPOSI modelWAN: Physical Layer standards• Describes the interfacebetween the DTE and the DCE• EIA/TIA-232, V.24 (DB25)• EIA/TIA-449 (DB37)• EIA-530 (DB25)• V.35 (DB34)• X.21 (DB15)• G.703 (BNC)www.connectworld.netWAN Standards: ProtocolsTypical WAN Layer 2 LinksLeased LineHDLC, PPP, SLIPX.25, Frame Relay, ATMServiceProviderPacket-switchedPPP, SLIP, HDLCCircuit-switchedTelephoneCompanyWAN: Data Link Layer standards•••SLIPí Serial Line Interface Protocolí Designed to carry IP packetsí Being replaced by PPPPPPí Point-to-Point Protocolí Support multiple network layerprotocols (IP, IPX, DecNET)í Operates over sync.
or async. linksSDLCí Synchronous Data Link ControlProtocolí IBM designed protocolí Point-to-point & multipoint linksí Operates over sync. links••••HDLCí High-Level Data Link Controlí IEEE standard from SDLCí Point-to-point and multipoint linksí Operates over sync. linksLAPBí Link Access Procedure Balancedí used by X.25 protocolLAPDí Link Access Procedure D-channelí ISDN D-Channel for control signalLAPFí Link Access Procedure Balancedí Used in Frame Relay for fast frameswitching over high-quality digitalfacilitiesA typical WAN setupWAN service provider toll networkSSSSCO SwitchLocal LoopSSSTrunks and switchesPoint-to-point orcircuit-switchedconnectionDemarcationCustomer PremisesEquipmentInternetwork with router•••••Consistent end-to-end addressingAddresses that represent network topologiesBest path selectionDynamic or static routingSwitchingAcademy approach to hands-on labs• In the academy lab,devices that make up theWAN cloud are simulatedby the connectionbetween the back-to-backDTE-DCE cables.RoutersIntroduction to routers in a WAN• A router is a special type ofcomputer.
It has a CPU, memory,a system bus, and variousinput/output interfaces.• Routers need the InternetworkOperating System software (IOS)to run configuration files.• Configuration files contain theinstructions and parameters thatcontrol the flow of traffic in andout of the routers.Router Component: CPU• The Central Processing Unit (CPU) executesinstructions in the operating system. Amongthese functions are system initialization, routingfunctions, and network interface control.• The CPU is a microprocessor.
Large routersmay have multiple CPUs.Router Component: RAM• RAM, also called dynamic RAM (DRAM), has thefollowing functions:–––––Stores routing tablesHolds ARP cacheHolds fast-switching cachePerforms packet buffering (shared RAM)Provides temporary memory for the configuration file of the routerwhile the router is powered on– Loses content when router is powered down or restartedRouter Component: RAM• RAM provides run time space for executableCisco IOS software and its subsystems.• RAM is usually logically divided into mainprocessor memory and shared input/output (I/O)memory.• RAM can be upgraded by adding additional DualIn-Line Memory Modules (DIMMs).Router Component: NRAM• NVRAM has the following characteristics andfunctions:– Provides storage for the startup configuration file– Retains content when router is powered down or restarted• In some devices it is implemented in the sameflash device.Router Component: Flash• Holds the operating system image (IOS)• Allows software to be updated without removing andreplacing chips on the processor• Retains content when router is powered down orrestarted• Can store multiple versions of IOS software• Is a type of electronically erasable, programmable ROM(EEPROM)• Adding or replacing the flash Single In-Line MemoryModules (SIMMs) or PCMCIA cards can upgrade theamount of flash.Router Component: ROM• Maintains instructions for power-on self test(POST) diagnostics• Stores bootstrap program and basic operatingsystem software, load Cisco IOS software fromFlash ro RAM• Some routers also have a scaled down versionof the IOS that can be used as an alternativeboot source.• Requires replacing pluggable chips on themotherboard for software upgradesRouter Component: Interfaces• Three types of interfaces are local-area network(LANs), wide-area network (WANs), andConsole/AUX.• Connect router to network for frame entry andexit, or connect to terminal for configuration• Can be on the motherboard or on a separatemodule (fixed or modular card)Router Component: Interfaces• LAN interfaces (Ethernet, FDDI, ATM..) and WANinterfaces(serial, ISDN, CSUs..) have controllerchips that provide the logic for connecting thesystem to the media.• The Console/AUX ports are serial ports usedprimarily for the initial configuration of therouter.Router Component: Power Supply• The power supply provides the necessary powerto operate the internal components.• Larger routers may use multiple or modularpower supplies.• In some of the smaller routers the power supplymay be external to the router.2600 External ConnectionManagement Ports• Provides a text-based connection for theconfiguration, monitoring and troubleshootingof the router• The common management interfaces are theconsole and auxilliary ports.
These are EIA-232asynchronous serial ports.• Computer must run a terminal emulationprogram to provide a text-based session withthe router.Management Ports ConnectionsManagement Ports Connections• The console port is preferred because itdisplays router startup, debugging, and errormessages by default.• The console port can also be used when thenetworking services have not been started orhave failed.
Therefore, the console port can beused for disaster and password recoveryprocedures.Connecting console interfaces• Configure terminalemulation software onthe PC for with theappropriate com portand settings.• Connect the RJ-45connector of therollover cable to therouter console port.• Connect the other endof the rollover cable tothe RJ-45 to DB-9adapter.• Attach the female DB-9adapter to a PCSummary••••••WANs characteristicsWANs standards and protocolsRouter internal componentsRouter functionsRouter management portsRouter LAN and WAN connectionCCNA2 – Module1.
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