Module 2: Introduction to Routers 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. Router User Interface The Cisco IOS software uses a command-line interface (CLI) as the traditional console environment. 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. Router User Interface Modes As a security feature the Cisco IOS software separates the EXEC sessions into two access levels. These levels are : 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 mode can be identified by the “>" prompt. The privileged EXEC mode accesses all router commands. 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. To access, the global configuration mode: Router>enable Router# config t To return to the user EXEC mode from the privileged EXEC mode, the disable command or exit may be entered. To return to the privileged EXEC mode from the global configuration mode, type exit or Ctrl-Z. Ctrl-Z is a command used to back out of configuration mode. This will return the user to the privileged EXEC mode prompt Cisco IOS software features 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. Show version and show flash must be issued to display the name of the active IOS. However, show flash displays all of the Cisco IOS image files on a router. Operation of Cisco IOS software The Cisco IOS devices have three distinct operating environments or modes: ROM monitor - performs the bootstrap process and provides low-level functionality and diagnostics. It is used to recover from system failures and to recover a lost password. The ROM monitor cannot be accessed through any of the network interfaces. It can only be accessed by way of a direct, physical connection through the console port. Boot ROM - When the router is running in boot ROM mode, only a limited subset of the Cisco IOS feature set is available. Boot ROM allows write operations to flash memory and is used primarily to replace the Cisco IOS image that is stored in flash. The Cisco IOS image can be modified in boot ROM by using the copy tftp flash command, which copies an IOS image stored on a TFTP server into the flash memory of the router. Cisco IOS - The normal operation of a router requires use of the full Cisco IOS image as stored in flash. In some devices, the IOS is executed directly from flash. However, most Cisco routers require a copy of the IOS to be loaded into RAM and also executed from RAM. Some IOS images are stored in flash in a compressed format and have to be expanded when copied to RAM. The startup process of the router normally loads into RAM and executes one of these operating environments. The configuration register setting can be used by the system administrator to control the default start up mode for the router. Initial Startup of Cisco Routers A router initializes by checking the hardware, loading the bootstrap, the operating system, and a configuration file. If the router cannot find a configuration file, it enters setup mode. Upon completion of the setup mode a backup copy of the configuration file may be saved to nonvolatile RAM (NVRAM). When a Cisco router powers up, it performs a power-on self test (POST). During this self test, the router executes diagnostics from ROM on all hardware modules. These diagnostics verify the basic operation of the CPU, memory, and network interface ports. After verifying the hardware functions, the router proceeds with software initialization. Steps in Router Initialization ROM Load Bootstrap Flash TFP server ROM CISCO Internetwork Operating Syatem NVRAM TFP server Console Setup is not intended as the mode for entering complex protocol features in the router. The purpose of the setup mode is to permit the administrator to install a minimal configuration for a router, unable to locate a configuration from another source. Router enters set up mode on the following conditions: after issuing the command Router#setup during the initial configuration of a router after deleting the backup configuration and reloading the router Configuration File In the setup mode, default answers appear in square brackets [ ] following the question. Press the Enter key to use these defaults. During the setup process, Ctrl-C can be pressed at any time to terminate the process. When setup is terminated using Ctrl-C, all interfaces will be administratively shutdown. Router LED indicators An interface LED indicates the activity of the corresponding interface. If an LED is off when the interface is active and the interface is correctly connected, a problem may be indicated. If an interface is extremely busy, its LED will always be on. The green OK LED to the right of the AUX port will be on after the system initializes correctly. Establishing HyperTerminal Session Take the following steps to connect a terminal to the console port on the router: 1. Connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9 or RJ-45 to DB-25 adapter. 2. Configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits, no parity, 1 stop bit, and no flow control. Keyboard Help in Router CLI Typing a question mark (?) at the user EXEC mode prompt or the privileged EXEC mode prompt displays a handy list of available commands. The "--More--" prompt at the bottom of the display indicates that multiple screens are available as output. Whenever a "--More--" prompt appears, the next available screen can be viewed by pressing the space bar. To display just the next line, press the Return or Enter key. Press any other key to return to the prompt. IOS Editing Commands Command CTRL-A Description Moves to the beginning of the command line ESC-B CTRL-B CTRL-E CTRL-F ESC-F Router Command History Moves back one word Moves back one character Moves to the end of the command line Moves forward one character Moves forward one word The user interface provides a history or record of commands that have been entered. This feature is particularly useful for recalling long or complex commands or entries. With the command history feature, the following tasks may be completed: Set the command history buffer size Recall commands Disable the command history feature The command history is enabled by default and the system records ten command lines in its history buffer. To change the number of command lines the system records during a terminal session, use the terminal history size or the history size command. The maximum number of commands is 256. To recall commands in the history buffer beginning with the most recent command, press Ctrl-P or the up arrow key repeatedly to recall successively older commands. To return to more recent commands in the history buffer, after recalling commands with Ctrl-P or the up arrow, press Ctrl-N or the down arrow key repeatedly to recall successively more recent commands. When typing commands, as a shortcut, the unique characters may be entered for a command. Press the Tab key, and the interface will finish the entry. When the typed letters uniquely identify the command, the Tab key simply acknowledges visually that the router has understood the specific command that was intended. Command line errors occur primarily from typing mistakes. If a command keyword is incorrectly typed the user interface provides error isolation in the form of an error indicator (^). The "^" symbol appears at the point in the command string where an incorrect command, keyword, or argument was entered. The error location indicator and interactive help system allow the user to easily find and correct syntax errors. The show version command The following information are provided from the show version command: IOS version and descriptive information Bootfield settings Amount of RAM Router up time Last restart method System image file and location Router platform Configuration register setting the number and types of interfaces on the router * the location to be used for loading the IOS Use the show version command to identify router IOS image and boot source.