INTRODUCTION TO IOS

AND CISCO ROUTERS By

Anil Kumar Vishwakarma

MCA,MCTS,CCNA

CISCO ROUTER IOS

oThe Cisco IOS (Internetwork Operating System) was

created to deliver network services and enable networked

applications. It runs on most Cisco routers.

oSome of the important things that the Cisco router IOS

software is responsible for include

o Carrying network protocols and functions.

o Connecting high-speed traffic between devices.

o Adding security to control access and stop unauthorized

network use.

o Supplying network reliability for connecting to network

resources.

CISCO ROUTER

Router uses to connect: -

Subnet with another Subnet (By LAN

Interface).

LAN with another LAN (By WAN Interface).

LAN with WAN (By WAN Interface).

WAN with another WAN (By WAN Interface).

Router Consist of External Components

(Interfaces) and Internal Components

INTERNAL COMPONENT

CONNECTING TO A CISCO ROUTER

You can connect to a Cisco router to configure

it, verify its configuration, and check statistics.

There are Three ways to do that: -

Console Session.

Auxiliary Session.

Telnet Session can’t use this method after router has

taken valid IP address.

COMPUTER CONSOLE CONNECTION

MODEM CONNECTION

BRINGING UP A ROUTER

When you first bring up a router, it will

takes this Boot Sequence: -

Perform POST (Power On Self Test) which is small program stored in ROM to check router components.

Load IOS image from Flash memory and decompress it into RAM.

Display the information from POST.

Running Valid Configuration (Startup Conf).

If no configuration router will go into Setup mode.

MEMORY ARCHITECTURE

MEMORY TYPES

RAM Used to store working tables as well as

running IOS image

ROM Stores a bootable IOS image that provides

basic functionality as well as a barebones interface called the ROM Monitor (ROMMON)

Flash Memory Stores the full function IOS image and is the

default location for IOS at boot

NVRAM Stores startup configuration file

MEMORY TYPES

RAM

(Working Memory)

Flash

(IOS)

ROM

(Basic IOS)

NVRAM

(Startup Config)

CONFIGURATION AND IOS

IMAGES

CONFIGURATION FILE

The configuration is a text file that contains configuration commands that are executed at startup

When the router boots a copy of the config in NVRAM (startup-config) is executed to establish the initial configuration

Configuration commands entered while the router is running are entered into the temporary configuration stored in RAM (running-config)

SAVING A CONFIGURATION

RAM

(Running-Config)

NVRAM

(Startup-Config)

Copy running-config startup-config

Copy startup-config running-config

Merged

Replaces

SYNTAX OF THE COPY COMMAND

Copy From-Location To-Location

Where:

From- and To-Location - {tftp|running-config|startup-config}

tftp – a trivial ftp server located somewhere on the network

ENTERING THE CONFIGURATION

Setup Mode If no configuration exists when the router

boots, it enters setup mode Router hasn‟t been configured before

Someone used the „Erase Startup-Config‟ then rebooted

NVRAM was damaged

Setup mode is a question and answer process that can be used to create basic configurations

Command Line Interface (CLI) Configuration commands entered at command

prompt then saved to NVRAM

SETUP MODE

Setup Mode allows configuration of: Interface summary

Router hostname

Passwords

SNMP

Various network protocols DECnet, Appletalk, IP, IPX

Routing protocols

Interfaces

When finished setup mode gives the user the option of copying the configuration to NVRAM and RAM

VIEWING CONFIGURATIONS

Show {running-config|startup-config}

THE CLI AND GETTING HELP

COMMAND LINE INTERFACE

Most Cisco devices use a command line

interface

Commands can be entered and edited

before they are executed by hitting the

enter key

Commands can be abbreviated as long as

they are not ambiguous

e.g. Show Interface => sh int

COMMAND LINE INTERFACE

If a command has an error the command will be repeated

and a “^” will mark the location of the error

access-list 110 permit host 1.1.1.1

^

%Invalid input detected at „^‟ marker.

COMMAND HISTORY

Up and Down arrows scroll through command history

Also ctrl+p (up) and ctrl+n (down)

Command history commands Show history – shows commands in history

Show terminal – shows terminal configurations and terminal history size (default = 10)

Terminal history size – changes history buffer size up to a max of 256

GETTING HELP

Typing ? at any point will cause IOS to show

what options exist at that point

Just ? on a line will list all commands available in

that mode

Typing one letter followed by ? will show all

commands that begin with the letter

Adding ? after a command will show what arguments

are available for the command

CONNECTING TO THE ROUTER

CONNECTING TO THE ROUTER

Console Connect directly to console port and use a terminal

program like Windows Hyperterminal or Linux‟s Minicom

AUX The auxiliary port is port you can attach a modem to

Can also be used as a backup connection dial on demand circuit

TTY Can use Telnet to connect to TTY once router has

been configured initially

Most routers have 5 TTY connections

IOS MODES

IOS MODES

User Mode

Router>

Privileged (Enable) Mode

Router#

disable enable

Telnet Aux Console

IOS CONFIGURATION MODES

Configuration Mode

Router(config)#

Privileged Mode

Router#

Config terminal

(config t)

Interface Configuration Mode

Router(config-if)#

Interface <interface>

(interface ethernet 0)

Router Configuration Mode

Router(config-router)#

Router <protocol>

(Router rip)

ROUTER INTERFACES

INTERFACES

LANs Ethernet (Ethernet 0, E0, E1, etc.)

FastEthernet (FastEthernet 0, F0, F1, etc.)

Token Ring (TokenRing 0, TO0, TO1, etc.)

WANs Serial 0, S0, S1, etc.

INTERFACES ON EXPANSION CARDS

Interfaces on add in expansion cards include the slot number followed by a slash then the interface number

The first FastEthernet interface on a card in the first slot would be FastEthernet 0/0

On 7500 series routers three values are required (slot/port-adapter/port) so it would be FastEthernet 0/0/0 for example

LOOPBACK INTERFACES

Loopback interfaces are internal interfaces and

treated like other interfaces

Loopback interfaces are never shutdown

Loopback interfaces are useful when you need an

interface that will never go down

INTERFACE CONFIGURATION MODE

Use the Interface command in configuration or

interface configuration mode to enter

configuration mode

Router(config)#interface e0

Router(config-if)#interface Lo0

Router(config)#interface s0/1

BRINGING UP AN INTERFACE

By default, all interfaces (except loopback

interfaces) are in administrative shutdown mode

To activate the interface use the no shutdown

command in the interface configuration mode

ASSIGNING AN IP ADDRESS

IP addresses are assigned in interface

configuration mode

Router#config t

Router(config)#interface s0

Router(config-if)#ip address 129.130.32.1 255.255.224.0

Router(config-if)#no shutdown

Router(config-if)#exit

SETTING THE CLOCK RATE

On serial connections the DCE must set a clock rate to synchronize communication In the lab the 2501 that is a router is a DCE

because the cable attached is a DCE cable so the clock rate must be set on this router

The 2501 that is a Frame Relay switch is also a DCE but you do not configure this one

Router(config)#int s0

Router(config-if)#clockrate 2000000

SETTING THE SERIAL

ENCAPSULATION

We‟ll discuss this in more detail later in the

semester but the data link layer protocol must be

set for the Frame Relay link using the

encapsulation command

Router(config)#interface s0

Router(config-if)#encapsulation frame-relay

PASSWORDS

PRIVILEGED MODE PASSWORDS

Enable password

Enable password <password>

Enable password is shown in clear text

Not used if enable secret password is set

Enable secret password

Enable secret <password>

Enable secret password is encrypted

USER MODE PASSWORDS

Console Line console 0 Login Password <password>

Auxiliary Line aux 0 Login Password <password>

Telnet Line vty 0 4 Login Password <password>

Enter configuration mode

Require login

Set password

Most routers have 5 telnet

lines. This command sets

all five.

ENCRYPTING PASSWORDS

User mode passwords are normally stored in the configuration file in clear text

To encrypt them use the following sequence of commands

service password-encryption line console 0 login password <password> no service password-encryption

IOS COMMANDS TO KNOW

Enable/disable Enable secret/password

Config

Editing commands

Show history

Show terminal

Terminal history size

Line How to require login and set password for

console, vty and aux

IOS COMMANDS TO KNOW

Service password-encryption

Banner

Interface Shutdown

Know the interfaces commands for ethernet, fast ethernet, serial, token ring and loopback

Description

Hostname

Show running/startup-config

Copy <running-config/startup-config,tftp> <running-config/startup-config,tftp>

IOS COMMANDS TO KNOW

Show interface

Show controllers

Clock rate

Ip address

Show Version

Show flash

Thank You