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Module 1. WANs and Routers. WANS. WAN operates at the physical layer and the data link layer of the OSI reference model. Provide connectivity over a large geographic area Use regional Bell companies Serial connections

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Module 1

Module 1

WANs and



  • WAN operates at the physical layer and the data link layer of the OSI reference model.

  • Provide connectivity over a large geographic area

  • Use regional Bell companies

  • Serial connections

  • Userouters, switches, modems (CSU/DSU), communication servers (dial-in, dial-out)

Routers & PCs

  • A router is a special type of computer.

  • It has the same basic components as a standard desktop PC.

  • It has a CPU, memory, a system bus, and various input/output interfaces.

  • Routers connect and allow communication between two networks and determine the best path for data to travel through the connected networks.

  • Routers need the Internetwork Operating System (IOS) software to run configuration files.

Router Internal Components

  • The main internal components of the router are random-access memory (RAM), nonvolatile random-access memory (NVRAM), flash memory, read-only memory (ROM), and interfaces.

Router internal components
Router Internal Components

RAM is used for routing table information and it holds the running configuration.

The interfaces provide LAN and WAN connectivity.

NVRAM is used to store the backup/startup configuration file.

The console port provides physical access for initial configuration.

Flash memory is used for storage of full Cisco IOS software images.

ROM is used for permanently storing startup diagnostic code.


  • Routers are mainly used as WAN devices.

  • Routers use WAN connections to communicate with each other.

  • Routers are the backbone devices of large intranets and of the Internet.

  • They operate at Layer 3 of the OSI model, making decisions based on network addresses.

Functions of a router
Functions of a Router

  • The two main functions of a router are to select the best path for packets and to route packets to the proper interface.

  • Routers build routing tables and exchange network information with other routers.

  • Routers segment local area networks

Functions of a Router Initiated by Router Configuration Files

  • Selection of BEST PATH for data

  • Controlling the flow of traffic in and out of the router (switching packets to appropriate interface)

  • Specifying the correct set up and use of routed and routing protocols

  • Routers do this by building a routing table and sharing that information with other routers.

An internetwork
An Internetwork Files

  • A correctly configured internetwork provides the following:

    • Consistent end-to-end addressing

    • Addresses that represent network topologies

    • Best path selection

    • Dynamic or static routing

    • Switching

Wan data link protocols
WAN Data Link Protocols Files

  • The primary functions of a WAN operate at the physical layer and at the data link layer.

  • The WAN physical layer describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE).

  • WAN data link protocols include the following:

    • High-level data link control (HDLC)

    • Frame Relay

    • Point-to-Point Protocol (PPP)

Academy Approach to WANs Files

  • In the academy lab, all the networks will be connected with serial or Ethernet cables.

  • In the real world serial cables are not connected back to back.

  • In a real world situation, one router could be in New York, while another router could be in Sydney, Australia.

  • In the academy lab, devices that make up the WAN cloud are simulated by the connection between the back-to-back DTE-DCE cables.

WAN Connections Files

Academy training simulates this DTE to DCE connection

We use

Connecting wan interfaces
Connecting WAN interfaces Files

  • A WAN uses many different technologies to make data connections across a broad geographic area.

  • WAN communication services are usually leased from service providers.

Router interfaces
Router Interfaces Files

  • LAN interfaces allow routers to connect to the LAN media. This is usually some form of Ethernet.

  • WANs provide connections through a service provider to a distant site or to the Internet.

Router management ports
Router Management Ports Files

  • Console

    • Used for initial configuration

    • Troubleshooting

    • Debugging

    • Monitoring the system

    • Displays startup and error messages by default (console only)

    • Do not depend on network connections

    • Actually asynchronous serial ports

  • Auxiliary (AUX)

    • Auxiliary for dial-in access

Initial connection to the router
Initial Connection to the Router Files

  • A rollover cable with a DB-9 to RJ-45 adapter

  • Connect to the console port of the router

  • Connect to to the COM port of a PC with terminal emulation software such as HyperTerminal

Configuring hyperterminal
Configuring HyperTerminal Files

  • Configure terminal emulation software on the PC for the following: