Cisco IOS: Configuration, Features, and Upgrading | Complete Guide – 2024

Cisco IOS Briefly Explained

 Cisco IOS Overview

Cisco IOS (Internetwork Operating System) is all Cisco routers and Catalyst switches that use a command line interface. The IOS gives the features to configure the Layer – 2 and Layer – 3 Cisco devices. Further, This Cisco IOS is formed on different modes and privilege levels to access the function.

The following example of an IOS command line interface

Router# show startup-config

In this example, the Router is the username, # is the mode, show is the command and startup-config is the arguments. Then hit the enter button to display the output of this command

The IOS version is formatted is as follows

x.y(Z)t

  • The X shows the major revision number
  • The Y shows the minor revision number
  • The Z shows the individual release number
  • The t shows the train identifier

The 3rd version of 12.4 IOS is noted as 12.4(3) and the combined major and minor versions are known as Maintenance Release number. T represents the specific market like

  • The T is known as Technology features and security fixes
  • The E is known as Enterprise Train for enterprise equipment
  • The S known as Service Provider gives the features for specific ISP devices

The latest version of IOS is 12.4(11)T. To view the current version of the IOS

Router# show version

This Cisco IOS is saved in Flash on a Cisco router in the format of. BIN file. Further, it can be upgraded by different methods

  • By replacing the existing Flash stick
  • By TFTP server
  • By Xmodem
  • By PCMCIA slot

The IOS .BIN file which is saved in Flash follows the specific naming conversion

C2600-ik9s-mz. 121-3.T.bin

The following .BIN file explanation of each component is as follows

  • C2600 – Cisco Hardware
  • Ik9s – Feature set
  • M – memory location
  • Z – Compression format
  • 121 – maintenance Release
  • 3 – Individual Release
  • T – Train identifier

Understanding of Cisco Router and Switches IOS Modes

As we discussed the Cisco IOS modes earlier in this guide. There are several Cisco IOS modes

USER EXEC mode

In this mode, no configuration can be changed or viewed, just the basic view is displayed

Router >

Privileged EXEC mode

In this mode, all configuration, settings, and status information can be viewed

Router#

Global Configuration Mode

In this mode, all configuration can be done by entering the configure terminal from Privileged mode

Router# configure terminal

Router(config)#

And type exists to return privileged mode

Router(config)# exit

Router(config)#

Further, the Global Configuration mode is sectioned into several sub-modes to perform specific actions. The most common modes are as follows

  • Interface Configuration mode – Router(config-if)#
  • Line Configuration mode – Router(config-line)#
  • Router Configuration mode – Router(config-router)#

 What are the differences between interface and lines?

Routers and switches are connected through interfaces and the traffic is routed through these interfaces. Lines identify the ports that give access to routers and switches to configure through Telnet, console port.

To configure the interface and lines

Router(config)# line console 0

Router(config-line)#

Router(config)# line vty 0 4

Router(config-line)#

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What is a Terminal History Buffer?

Cisco IOS maintains the record of previously entered commands. By default, it stores the 10 previously entered commands or you can adjust the buffer from 0 – 256.

To View the history

RouterA# show history

Enable

Config t

RouterA# terminal history size 30

IOS Context-Sensitive Help

The question mark (?) is the powerful tools to explore the commands at that mode of configurations

Router # ?

Further, SHOW command provides the configurations and status of the router

Router# show version

How to Configure Cisco Router Password?

Enable Password:

This password secures your router at privileged mode and changes from Global configuration mode

Router(config)# enable password cisco

Router(config)# enable secret cisco

Line Password and Configuration

Password can be set additionally on router lines such as Telnet and console

To configure these lines

Router(config)# line console 0

Router(config)# login

Router(config-line)# password cisco1234

Router(config)# line vty 0 4

Router(config)# login

Router(config-line)# password cisco1234

Managing the Configuration Files:

Cisco IOS has contains two separate file

  • Running-config – stored in RAM contains the current configurations
  • Startup-config – stored in NVRAM contains the save configurations

Additionally, To save the current configuration, copy the running files and store into save files 

Router# copy running-config startup-config

We can use the shortcut to simplify the commands

Router# copy run start

To erase the content of the startup file

Router# erase start

What is the Piping Command?

The Piping will help remove irrelevant information from the output and show you the exact configuration you desire to see. The Pipe can do this | character

This command shows the beginning of the configuration with the start Ethernet

Router# show startup | begin Ethernet

This command displays the configuration by excluding all lines with the text Ethernet

Router# show startup | exclude Ethernet

This command displays the configuration that include all lines with the text Ethernet

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