CCNA2 Chapter 1

Wide Area Networks and Routers

WAN is a data communications network that operates beyond a LAN’s geographic scope.

Users subscribe to a WAN provider such as AT&T, Sprint, etc. These providers offer network services such as:

• Frame Relay

• Integrated Services Digital Network (ISDN)

• Asynchronous Transfer Mode (ATM)

These services carry different traffic types: voice, data and video.

WAN’s operate at the first three layers of the OSI. (Frame Relay actually operates at layer 1 and layer 2.) All of the WAN services have layer 1 & layer 2 in common.

Other characteristics of WAN are:

1. operate past LAN geographic area

2. use serial connections

3. provide full-time & part-time connectivity

WAN – Wide Area Networks

Router Internal Components

• Main internal components of the router

1. Random-access memory (RAM)

2. Nonvolatile random-access memory (NVRAM)

3. Flash memory

4. Read-only memory (ROM)

5. Interfaces

•RAM

• stores routing tables

• holds ARP cache

• holds fast-switching cache

• performs packet buffering

• maintains packet-hold queues

• provides temporary memory for the configuration file of the router while the router is powered on

• loses content when router is powered down or restarted

Router Internal Components

NVRAM

• provides storage for the startup configuration file

• retains content when router is powered down or restarted

Router Internal Components

Flash memory

• holds the operating system image (IOS)

• allows software to be updated without removing & replacing chips on the processor

• retains content when router is powered down or restarted

• can store multiple versions of IOS software

• is electronically erasable, programmable ROM (EEPROM)

Router Internal Components

ROM

• maintains instructions for power-on self test (POST) diagnostics

• stores bootstrap program & basic operating system software

• requires replacing pluggable chips on the motherboard for software upgrades

Router Internal Components

Interfaces

• connect router to network for frame entry and exit

• can be on the motherboard or on a separate module

• connect the router to LANs and WANs

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.

Router Internal Components

DTE DCERouter

Modem

Example: interface between the Data Terminal Equipment (DTE) such as a router to the Data Circuit-Terminating equipment (DCE) to the WAN network such as a modem.

DTE is on the customer’s side of the network. - converts user information into signals for transmission, or reconverts the received signals into user information

The DCE - is typically a modem and in many cases is circuitry in a CO, switch which is made up of a CSU/DSU (Channel Service Unit/Data Service Unit). The major reason for CSU/DSU is to protect the equipment from CPE/DTE from aberrant voltages, and to ‘square’ up the signal.

DCE is usually on the provider’s side. - A device that establishes, maintains and terminates a session on a network. It may also convert signals for transmission. It

Subscriber to Provider Interface

Sample Lab Setup

DTE DCERouter

Modem

EIA/TIA-232, V.35, X.21, HSSI, others

Subscriber to Provider Interface

The 3 basic types of connections on a router are:

1. LAN interfaces

2. WAN interfaces

3. Management ports

• Console

• auxiliary

Router Physical Characteristics

Management ports provide

• Text-based connection

• Configuration, monitoring, password recovery and troubleshooting

The management ports:

• EIA-232 asynchronous serial ports

• used for non-network connections

• used for initial router configuration

• to connect to a port, a PC must have a terminal emulation program

• rollover cable from PC to the management ports

Router Physical Characteristics

The console port, says Cisco is preferred when troubleshooting:

• doesn’t depend on network services

• displays start and error messages by default

To establish a connection between PC and a router, one needs

• terminal emulation software

• rollover cable

• RJ-45 to DB-9 connector

Management Ports

Cisco says, the terminal emulation software, HyperTerminal, the parameters used to configure a router are:

• Data bits

• Stop bits

• parity

Router Physical Characteristics

For a PC of a LAN to connect to a router, one

• straight-thru cable from the PC to a HUB or switch

• straight-thru cable from the HUB or switch to router’s Ethernet interface

Router’s connection LAN and WAN

An internetwork must include:

• switching

• dynamic or static routing

• consistent end-to-end addressing

Router’s connection LAN and WAN

DTE DCERouter

Modem

EIA/TIA-232, V.35, X.21, HSSI, others

The connections to WAN on router is through the serial interface, either as a Smart Serial interface connector or DB-60 connector.

The following devices are used in the construction of a WAN:

• communication servers

• routers

• modems

Router’s connection LAN and WAN

According to Cisco, the common components between a router and PC are:

1. CPU

2. input/output interfaces

3. system bus

Router vs. PC

OSI Model

Data unit Layer Function

Hostlayers

Data

Application Network process to application

Presentation

Data representation and encryption

Session Interhost communication

Segments Transport End-to-end connections and reliability (TCP)

Medialayers

Packets NetworkPath determination and logical addressing

(IP)

Frames Data link Physical addressing (MAC & LLC)

Bits Physical Media, signal and binary transmission