CCNA2 Chapter 2

Cisco IOS Software

Cisco’s operating system is called Cisco Internetwork Operating System (IOS)

IOS provides the following network services:

• basic routing and switching functions

• reliable and secure access to networked resources

• network scalability

Cisco IOS Software

Cisco IOS software uses a command-line interface (CLI) as the console environment.

This environment is accessible via:

• console session

Uses a low speed serial connection directly from PC to router

• AUX port

Dialup with a modem through AUX port. Don’t need the router to be connected to network services

• Telnet

Must have at least one interface configured with IP address, and virtual terminal sessions must be configured for login & password.

Access to Routers

The Cisco CLI uses a hierarchical structure, called modes.

The IOS provides a command interpreter service known as the command executive (EXEC).

For security reasons, Cisco routers have two access levels:

• user EXEC mode

Has limited number of basic monitoring commands.

This mode is identified by > (Example: Router>)

• privileged EXEC

Requires password

May require an user ID

Users can accesses all router commands

This mode is identified by # (Example: Router#)

Cisco IOS Software

Cisco IOS releases naming convention contain 3 parts:

• platform on which the image runs

• special features supported in the image

• where the image runs and whether it has been zipped or compressed

It is of the form: xxxx-yyyy-ww

• xxxx = Platform

• yyyy = Features

• ww = Format – where it executes

Cisco IOS Software

Before installing a new Cisco IOS software image on the router, check to see if the router meets the memory requirements.

Use the command: show version

Cisco IOS Software

• To find out amount of flash memory, use the command: show flash

Cisco IOS Software

show version command displays:

• 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 (how IOS is booted)

Router Commands

IOS version

Boot ROM version

Router up time

Last restart method

System image file & location

Configuration register setting

Number & type of interfaces on the router

•Platform

•Feature set

•Location to be used for loading the IOS

This command will show all of the Cisco IOS image files – not just the one that the router booted from.

Might compare to a directory listing

Cisco IOS has 3 distinct operating environments or modes:

• ROM monitor

Performs the bootstrap processProvides low-level functionality and diagnostics. Used for password recovery. Can NOT be accessed through any interface.

• Boot ROM

Only a limited subset of Cisco IOS features are available. One is allowed to write to flash memory & is used primarily to replace the Cisco IOS image stored in flash

• Cisco IOS

Needs the full IOS image as stored in flash

Cisco IOS Software

The major steps in initialization of a router are:

• Power up self test (POST)

• Bootstrap loader in ROM executes

• Locate and load the operating system

• Locate and load the configuration files

Initial Startup

• Bootstrap loader

Simple set of instructions that tests hardware and initializes the IOS

• Locate and load IOS (determined where by the configuration register stored in NVRAM (if indicates Flash, then looks for boot system comands; if none, the default is:)

• Flash• TFTP server• ROM

• locate and load configuration files

• NVRAM• TFTP server

• Console

If no TFTP server is found, then the setup dialog is initiated.

Initial Startup

• Setup mode is not intended to be used to enter complex protocol features in a router.

• The purpose of the setup mode is to permit administrators to install a basic configuration for routers when a configuration cannot be obtained from another source.

• In the setup mode, default answers appear in square brackets [ ] following the question.

• Pressing the Enter key accepts these defaults. • During the setup process, Ctrl-C can be pressed at

any time to terminate the process.

Setup Mode

• The router will enter setup mode when:– The contents of NVRAM have been erased with the “erase

start” command– The router is “out of the box” and has not been initially

configured– After deleting the backup configuration and reloading the

router• You can make the router enter setup mode by entering:

– Router#setup

Setup Mode

After the system initializes correctly, the LED to the right of the AUX port will become green. (2600 light is in the front)

Initial Startup

The default parameters for the console port are:

• console port: 9600 baud• data bits: 8• no parity• 1 stop bit• no flow control

HyperTerminal

• User (User EXEC) mode Router>

• Privilege mode Router#

• Global configuration mode Router# config t

Only accessible from the privilege mode.

From this mode one can access:

• interfaces

• sub interfaces

• line

• router

• router-map

Router Modes

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Ctrl-A – moves to the beginning of the command line

Esc-B – move back one word

Ctrl-B – move back one character (left arrow)

Ctrl-E – move to the end of the command line

Ctrl-F – move forward one character (right arrow)

Esc-F – move forward one word

Ctrl-P – recalls last or previous command (up arrow)

Ctrl-N – recalls most recent command (down arrow)

<Tab> - complete the entry

Router HELP commands

Using the Help System

Router HELP commands

Maximum number of commands in the history buffer is 256

Router Command History