This tutorial covers basic Cisco IOS commands, intended for first time users.

What is Cisco IOS ?

Cisco IOS (Internetwork Operating System) is an OS used by majority of Cisco routers and switches (older switch used Cat OS). The first IOS was written by William Yeager and Gami Tumambing.

Cisco IOS has a CLI (command line interface) characteristics. It has two major mode, privileged and normal mode.
In privileged mode you can configure the router and the normal mode is used for checking the configuration.

Basic Configuration

To enter the privileged mode enter the following command.

Router>enable
Router#

Note the hash at the end of the router hostname Router#. This means the router is in privileged mode.

Before configuring anything, you have to enter the configuration mode.

Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#

Note the prompt changed to “Router(config)#”. This is the configuration mode for Cisco IOS.

At anytime if you want to check what command is available under certain mode, you can use “?” to list all the commands available

Router(config)#?
Configure commands:
  aaa                         Authentication, Authorization and Accounting.
  aal2-profile                Configure AAL2 profile
  access-list                 Add an access list entry
  alarm-interface             Configure a specific Alarm Interface Card
  alias                       Create command alias
  alps                        Configure Airline Protocol Support
  appfw                       Configure the Application Firewall policy
  appletalk                   Appletalk global configuration commands
  application                 Define application
....

Now to change the host name of the router, enter hostname command under config mode.

Router(config)#hostname R1
R1(config)#

Note that the command prompt is changed to R1 to reflect the new host name

Saving the Configuration

Cisco IOS is designed to save all these changes in RAM. So in case if you mess up something, you can just reload the router, and get everything back the the way it was.

Once you are satisfied with it, you can save the configuration to the permanent storage (NVRAM). First you have to exit the config mode, and then run the commands.

R1(config)#exit
R1#
*Mar  1 00:35:42.031: %SYS-5-CONFIG_I: Configured from console by console
R1#copy running-config startup-config
Destination filename [startup-config]?
Building configuration...
[OK]
R1#

That concludes tutorial #1 :-). If you have any question just post it in the comment section.