Module 2. Introduction to Routers. Cisco IOS Software. As with a computer, a router or switch cannot function without an operating system. The Cisco Internetwork Operating System (IOS) Also now used in the Catalyst switches IOS provides Basic routing & switching functions
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Module 2 Introduction to Routers
Cisco IOS Software • As with a computer, a router or switch cannot function without an operating system. • The Cisco Internetwork Operating System (IOS) • Also now used in the Catalyst switches • IOS provides • Basic routing & switching functions • Access to networked resources • Network scalability
Accessing the Command Line Interface • The command line interface (CLI) is accessed 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.
Router Configuration Modes • The Cisco CLI uses a hierarchical structure. • This structure requires entry into different modes to accomplish particular tasks. • Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode.
Router Configuration Modes • 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.
User 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.
Privileged EXEC Mode • The privileged EXEC mode provides access to all router commands. • This mode can be configured to require a password. • 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.
Privileged EXEC Mode • 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 will change to #.
IOS software and features • Cisco continues to develop different IOS software images to optimize the Cisco IOS software that these various platforms require. Each image represents a different feature set that serves the various device platforms, available memory resources, and customer needs. • Use the Cisco Software Advisor to obtain current Cisco IOS software information.
IOS software and 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
IOS software and features • One of the main considerations when selecting a new IOS image is compatibility with the router flash and RAM memory. • Use the show version command on the Cisco device to check the current image and available flash.
IOS version • Platform • Feature set • Location to be used for loading the IOS Boot ROM version Router up time System image file & location Last restart method Number & type of interfaces on the router Configuration register setting
This command will show all of the Cisco IOS image files – not just the one that the router booted from. Might compare to a directory listing
Three Operating Environments • The 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. • It can only be accessed by way of a direct, physical connection through the console port. • When the router is running in boot ROM mode, only a limited subset of the Cisco IOS feature set is available.
Step 1 Hardware check Bootstrap loader in ROM executes Step 2 Step 3 Operating system loads The configuration file is loaded if one is found in NVRAM Step 4 No configuration is in NVRAM, it looks for TFTP server, then SETUP from console Step 5 A Router Starts Up When a Cisco router powers up, it performs a power-on self test (POST).
Steps in Router Initialization 1 2 3 1 2 3
Setup Mode • Setup mode is not intended to be used to enter complex protocol features in a router. • The purpose of the setup mode is to permit administrators to install a basic configuration for routers when a configuration cannot be obtained from another source. • 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.
Setup Mode • The router will enter setup mode when: • The contents of NVRAM have been erased with the “erase start” command • When the router is “out of the box” and has not been initially configured • After deleting the backup configuration and reloading the router • You can make the router enter setup mode by entering: Router#setup
Understanding LED indicators on the router • This green light means that the system is on and has initialized properly. • An interface LED indicates the activity of the corresponding interface. • A problem may be indicated if an LED is off
Items Needed to Initially Configure a Router Rollover cable DB-9-to-RJ-45 on the PC serial port RouterConsole port
Two Levels of Access • To enter commands and configure a Cisco router, a user must log into the router to access the user interface. • For security purposes, a Cisco router has two levels of access.
Two Levels of Access • To enter privileged EXEC mode, type enable at the > prompt. • If a password has been set, enter it at the password: prompt. • Two commands can be used to set a password used to access privileged EXEC mode: • - enable password password • - enable secret password • If both commands are used, the enable secret command takes precedence.
Logging into the router • Once into the privileged EXEC mode, it becomes the “jumping off place to go to other configuration modes: Router>enable Password: xxxxxx Router#configure terminal Router(config)#interface serial 0 Router(config-if)#exit Router(config)#line con 0 Router(config-line)#login Router(config-line)#exit Router(config)#exit Router#disable Router> Ctrl-Z or end may be used at any time to return to privileged mode from anywhere
ROUTER MODES Router > User mode Router # Privileged mode Router(config)# Global configuration mode From the global configuration mode, you can enter specific configuration modes Interface configuration mode Router(config-if)# Line configuration mode Router(config-line)# Router configuration mode Router(config-router)#
Using the Help System • ? shows available commands for a particular mode • There are different commands for user and privileged, and even different commands for global mode. • show? Would give a list of show commands • s? would give all commands that begin with the letter “S” • If you can’t remember the command but know what it starts with, use the ? after the first letter or two.
Using the Help System • The --More-- prompt indicates that there are multiple screens of output. • When a --More-- prompt appears, press the Spacebar to view the next available screen. • To display just the next line, press the Return or Enter key. • Press any other key to return to the prompt.
Editing Commands • <Ctrl><A> Move to beginning of line • <Ctrl><E> Move to the end of the line • <Esc><B> Move back one word • <Ctrl><F> Move forward one character • <Ctrl><B> Move back on character • <Esc><F> Move forward one word • $ Sign means that the line has scrolled to the left • To disable enhanced editing mode, type terminal no editing at the privileged EXEC mode prompt.
Router Command History Maximum number of commands in the history buffer is 256