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CCNA 2 v3.1 Module 2

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CCNA 2

Module 2

Introduction to Routers

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Cisco IOS

• Cisco Internetwork Operating System is the software that controls routing and switching functions of internetworking devices

• Network services provided by Cisco IOS :

Basic routing and switching functions

Reliable and secure access to networked resources

Network scalability

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User Router Interface

• Cisco IOS software uses a command-line interface (CLI)

• This environment is accessible through several methods.

Console session

Uses a low speed serial connection directly from a computer or terminal to the console connection on the router

No initial configuration necessary

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Dialup connection:

Using a modem or null modem connected to the router AUX port.

No initial configuration necessary

Telnet session:

At least one interface must be configured with an IP address, and virtual terminal sessions must be configured for login and passwords.

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Router user interface modes

• CLI uses a hierarchical structure.

• Entry into different modes to accomplish tasks

E.g., To configure a router interface, the user must enter interface configuration mode.

• Command executive (EXEC): Validates and executes the entered commands.

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• IOS software separates the EXEC sessions into two access levels:

User EXEC mode

Privileged EXEC mode (enable)

• User EXEC mode (view only)

Limited number of basic monitoring commands

To check and view the router status

Cannot change the configuration of the router

Prompt >

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• Privileged EXEC mode (enable mode)

Accesses all router commands

Configuration and management

To ensure authorized users access this mode

Configured it to require a password from the user before accessing it & User ID

Provides access to

Global configuration mode and others

Prompt #

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Entering a question mark (?) at the privileged EXEC level will reveal many more command options than those available at the user EXEC level.

Type enable to enter privileged exec mode

Type disable to enter privileged exec mode

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IOS Naming Conventions

Platform (Hardware): C1005

Features: “b”, Appletalk 40 = 40 bit encryption

Format: F = Flash, M = RAM

Compression: Z = Zip compressed

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• Consideration when selecting a new IOS image

Compatibility with the router flash and RAM memory

i.e., is there enough space

To find this information use show version

• router#show version

Displays the amount of available RAM

…cisco 1721 (68380) processor (revision C) with 3584K/512K bytes of memory.

3584k main memory

512k shared memory

• router#show flash

Displays the amount of flash memory

…15998976 bytes total (10889728 bytes free

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Operation of Cisco IOS Software

• The startup process of the router normally loads into RAM and executes one of three operating environments/ modes.

ROM monitor

Boot ROM

Cisco IOS

• Systems administrator uses the configuration register setting to control the default start up mode for the router

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• ROM Monitor:

provides low-level functionality and diagnostics

used to

recover from system failures

recover a lost password

Can only be accessed by direct, physical connection through the console port

Prompt: ROMMON>

• Boot ROM :

Prompt: Router(boot)>

Offers only limited IOS features

Used for flash image updates

copy tftp flash

copies an IOS image stored on a TFTP server into the flash memory of the router

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• Cisco IOS

Normal operating mode

Usually stored in Flash but run from RAM

Prompt: router>

• show version

Displays

IOS image and version

Configuration register setting

Amount of available RAM

• show flash

Displays the amount of flash memory

Used to verify that the system has sufficient memory to load a new Cisco IOS image

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Initial startup of Cisco routers

If the router cannot find a configuration file, it enters “setup mode”. It is a basic configuration

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Startup routines must accomplish 3 things

Make sure that the router hardware is tested and

functional.

Find and load the Cisco IOS software

Flash, TFTP Server, ROM

Find and apply the startup configuration file or enter

the setup mode

NVRAM, TFTP Server, Console

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Router Startup Sequence1. Powers up

2. Performs a power-on self test (POST)

Executes diagnostics from ROM to check all hardware modules

This verifies basic operation of CPU, memory, network interface ports

3. Software initialization

The boot field of the configuration register determines the location to be used in loading the IOS.

Flash (0X2102), TFTP Server, ROM

IOS Software is loaded

List of hardware and software is displayed on console screen

4. If valid configuration file exists

Configuration file from NVRAM is loaded into main memory

start routing processes, supply addresses for interfaces

5. If no valid configuration file exists

Operating system searches for TFTP server

If no TFTP server the setup dialog is initiated

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• Entered only if configuration file cannot be found in NVRAM or TFTP

• Permits administrator to enter minimal router configurations

• Default answers appear in [ ]

• Press Enter to use these defaults

• Press Ctrl-C at any time

to terminate the process(setup mode)

all interfaces will be administratively shutdown

Setup Mode

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Router LED indicators

• An interface LED indicates the activity of the corresponding interface.

A green OK LED indicates system is initialized correctly

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Examining the initial router bootup Output

Output indicates a problem with the “NVRAM”. It could be “Write erased”

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Router Output Tells

• Bootstrap version

• IOS version the router

• Router model

• Processor

• Number of interfaces

• Types of interfaces

• Amount of NVRAM

• Amount of flash memory

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Logging into the router

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• When entering the Privilaged exec mode if the password: prompt is displayed, enter the password that has been set

• Password commands to access privileged EXEC mode

Router(config)# Enable password <password>

Not encrypted

Router(config)#Enable secret <password>

Encrypted

Cannot be the same as enable password

Takes precedence over enable password

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• From the Privileged mode you can enter the “Global Mode” & can configure the following;

Interface

Subinterface

Line

Router

Route-map

• To return to the privileged mode type Ctrl Z.

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Keyboard help in the router CLI

• Typing a question mark (?) displays a handy list of available commands. (user or privileged modes)

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• “?” can also be used to complete incomplete commands

Eg .. Setting the router clock

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• The "^" symbol appears at the point in the command string where an incorrect command, keyword, or argument was entered.

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Enhanced editing commands

“$” sign indicates that the command has scrolled onto the next line.

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Router command history

The maximum number of commands held is 256.

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The show version command

• show version command:

IOS version and descriptive information

Bootstrap ROM version

Boot ROM version

Router up time

Last restart method

System image file and location

Router platform

Configuration register setting

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