Content Overview Cisco technology is built around the Cisco Internetwork Operating System (IOS), which is the software that controls the routing and switching functions of internetworking devices. A solid understanding of the IOS is essential for a network administrator. This module will present an introduction to the fundamentals of the IOS and will provide practice in examining the features of the IOS. All network configuration tasks, from the most basic to the most complex, require a strong foundation in the basics of router configuration. This module will provide the tools and techniques for basic router configuration that will be used throughout this course.Students completing this module should be able to:

Describe the purpose of the IOS
Describe the basic operation of the IOS
Identify various IOS features
Identify the methods to establish a command-line interface (CLI) session with the router
Move between the user command executive (EXEC) and privileged EXEC modes
Establish a HyperTerminal session on a router
Log into a router
Use the help feature in the command line interface
Troubleshoot command errors

Content 2.1 Operating Cisco IOS Software 2.1.1 The purpose of Cisco IOS Software As with a computer, a router or switch cannot function without an operating system. Cisco calls its operating system the Cisco Internetwork Operating System or Cisco IOS. It is the embedded software architecture in all of the Cisco routers and is also the operating system of the Catalyst switches. Without an operating system, the hardware does not have any capabilities. The Cisco IOS provides the following network services:

Basic routing and switching functions
Reliable and secure access to networked resources
Network scalability

Web Links Cisco IOS® Software Overview http://www.cisco.com/warp/ public/732/

Content 2.1 Operating Cisco IOS Software 2.1.2 Router user interface The Cisco IOS software uses a command-line interface (CLI) as the traditional console environment. The IOS is a core technology that extends across most of the Cisco product line. Its operation details may vary on different internetworking devices. This environment is accessible through several methods. One way to access the CLI is through a console session. A console uses a low speed serial connection directly from a computer or terminal to the console connection on the router. Another way to access a CLI session is by use of a dialup connection using a modem or null modem connected to the router AUX port. Neither of these methods require that the router have any network services configured. Another method of accessing a CLI session is to Telnet to the router. To establish a Telnet session to the router, at least one interface must be configured with an IP address, and virtual terminal sessions must be configured for login and passwords.

Content 2.1 Operating Cisco IOS Software 2.1.3 Router user interface modes The Cisco command-line interface (CLI) uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks. For example, to configure a router interface, the user must enter interface configuration mode. From interface configuration mode, all configurations entered apply only to that particular interface. Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode. The IOS provides a command interpreter service known as the command executive (EXEC). After each command is entered, the EXEC validates and executes the command. As a security feature the Cisco IOS software separates the EXEC sessions into two access levels. These levels are user EXEC mode and privileged EXEC mode. The privileged EXEC mode is also known as enable mode. The following are the features of the user EXEC mode and privileged EXEC mode:

The user EXEC mode allows only a limited number of basic monitoring commands. This is often referred to as a “view only” mode. The user EXEC level does not allow any commands that might change the configuration of the router. The user EXEC mode can be identified by the “>" prompt.
The privileged EXEC mode accesses all router commands. This mode can be configured to require a password from the user before accessing it. For added protection, it can also be configured to require a user ID. This allows only authorized users to access the router. Configuration and management commands require that the network administrator be at the privileged EXEC level. Global configuration mode and all other more specific configuration modes can only be reached from the privileged EXEC mode. The privileged EXEC mode can be identified by the "#" prompt.

To access the privileged EXEC level from the user EXEC level, enter the enable command at the “>” prompt. If a password is configured, the router will then ask for that password. For security reasons, a Cisco network device will not show the password that is entered. When the correct password is entered, the router prompt changes to “#”, indicating that the user is now at the privileged EXEC level. Entering a question mark (?) at the privileged EXEC level will reveal many more command options than those available at the user EXEC level. Lab Activity e-Lab Activity: Logging into the Router This purpose of this lab is to access the router command-line interface and activate privileged level configuration options. Lab Activity e-Lab Activity: Router User Interface Modes In this lab, the students will learn to use the enable command to enter into privileged EXEC mode on the Cisco IOS. Web Links Routing Basics 101 http://www.cisco.com/warp/public/779/ smbiz/community/ routing_basics_101.htmlCisco IOS Basic Skills http://www.cisco.com/univercd/cc/td/ doc/product/ access/ acs_mod/ 1600/1600swcf/ swskills.htm

Content 2.1 Operating Cisco IOS Software 2.1.4 Cisco IOS software features Cisco provides IOS images for devices spanning a wide range of network product platforms. To optimize the Cisco IOS software that these various platforms require, Cisco is working to develop many different Cisco IOS software images. Each image represents a different feature set that serves the various device platforms, available memory resources, and customer needs. Although there are numerous IOS images for different Cisco device models and feature sets, the basic configuration command structure is the same. The configuration and troubleshooting skills acquired on any one device apply across a wide range of products. The naming convention for the different Cisco IOS releases contains three parts:

The platform on which the image runs
The special features supported in the image
Where the image runs and whether it has been zipped or compressed

Specific IOS features can be selected using the Cisco Software Advisor. The Cisco Software Advisor is an interactive tool that provides the most current information and allows the selection of options that meet network requirements. One of the main considerations when selecting a new IOS image is compatibility with the router flash and RAM memory. In general, the newer the release and the more features that it provides, the more memory it requires. Use the show version command on the Cisco device to check the current image and available flash. The Cisco support site has tools available to help determine the amount of flash and RAM required for each image. Before installing a new Cisco IOS software image on the router, check to see if the router meets the memory requirements for that image. To see the amount of RAM, issue the show version command: … <output omitted>… cisco 1721 (68380) processor (revision C) with