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Module 1WANs and

Routers

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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

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

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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.

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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.

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Router Internal Components

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

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

used for storage of full Cisco IOS software images.

ROM is used for permanently storing startup diagnostic code.

The console port provides physical access for initial configuration.

The interfaces provide LAN and WAN connectivity.

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Routers

• 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.

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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

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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.

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An Internetwork

• 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

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WAN Data Link Protocols

•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)

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Academy Approach to WANs

•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.

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WAN Connections

We useAcademy training simulates this DTE to DCE connection

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Connecting WAN interfaces

•A WAN uses many different technologies to make data connections across a broad geographic area. •WAN communication services are usually leased from service providers.

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Router Interfaces

• 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.

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Router Management Ports

• 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

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Initial Connection to the Router

• 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

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Configuring HyperTerminal

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