Introduction to the Cisco IOS

Introduction to IOS and Cisco Routers

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 ModeRouter>

Privileged (Enable) ModeRouter#

disable enable

Telnet Aux Console

IOS Configuration Modes

Configuration ModeRouter(config)#

Privileged ModeRouter#

Config terminal (config t)

Interface Configuration ModeRouter(config-if)#

Interface <interface>(interface ethernet 0)

Router Configuration ModeRouter(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 tRouter(config)#interface s0Router(config-if)#ip address 129.130.32.1 255.255.224.0Router(config-if)#no shutdownRouter(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 s0Router(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 s0Router(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 0LoginPassword <password>

AuxiliaryLine aux 0Login Password <password>

TelnetLine vty 0 4LoginPassword <password>

Enter configuration mode

Require login

Set password

Most routers have 5 telnetlines. This command setsall 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-encryptionline 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