Introduction to Routers

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Introduction to Routers

• CCNA 2 v 3.0
• Module 2

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The Cisco IOS

• The Cisco IOS (Internetwork Operating System) is
  the operating system of all Cisco routers and
  Catalyst switches
• The IOS provides the following network services
• Basic routing and switching functions
• Reliable and secure access to networked resources
  
• Network scalability
• The Cisco IOS software uses a command-line
  interface (CLI) as the traditional console
  environment.

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Methods of Accessing the CLI

• Through a console session
• uses a low speed serial connection directly from
  a computer or terminal to the console connection
  on the router
• Through a dialup connection
• uses a modem connected to the router AUX port
• Note Neither of the above methods require that
  the router have any network services configured
• Telnet 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.

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Router User Modes

• The Cisco command-line interface (CLI) uses a
  hierarchical structure
• The are two access levels
• user EXEC mode
• privileged EXEC mode (also called enable mode)

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User EXEC vs. Privileged EXEC

• User EXEC mode
• allows only a limited number of basic monitoring
  commands
• referred to as a view only mode
• cannot change router configuration
• identified by the gt" prompt
• Privileged EXEC mode
• accesses all router commands (including
  configuration)
• can be configured to require a password and user
  ID so that only authorized users access the
  router.
• Global configuration mode and all other more
  specific configuration modes can only be reached
  from the privileged EXEC mode
• identified by the "" prompt

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Moving Between User EXEC and Privilege EXEC
or en for short
or dis for short
or ex for short
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Cisco IOS Software Features

• There are numerous IOS images for different Cisco
  device models and feature sets
• But basic configuration command structure is the
  same
• Configuration and troubleshooting skills acquired
  on any one device apply across a wide range of
  products
• The Cisco Software Advisor is an interactive tool
  that provides the most current information and
• allows for the selection of options that meet
  network requirements.

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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

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The Show Version Command

• When selecting a new IOS image
• Make sure it is compatibility with the router
  flash and RAM memory
• Newer releases have more more features and
  require more memory
• Before installing, check to see if the router
  meets the memory requirements for that image
  which include
• Flash Memory
• RAM

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The Show Version Command

• Use the show version command to
• Check the current IOS image
• The Cisco support site has tools available to
  help determine the amount of flash and RAM
  required for each image
• Check the amount of RAM
• Show the configuration-register

IOS Image file
RAM
Configuration register
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The Show Version Command

• The following information can be obtained from
  the show version command
• IOS version and descriptive information
• Bootstrap ROM version
• Boot ROM version
• Router up time
• Last restart method
• System image file and location
• Router platform
• Configuration register setting
• Number and type of interfaces on the router
• NOTE Use the show version command to identify
  router IOS image and boot source

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Show Flash Command

• To find out the amount of flash memory
• issue the show flash command

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Operating Environments

• The Cisco IOS devices have three distinct
  operating environments or modes
• ROM monitor (cannot be accessed through any of
  the network interfaces)
• Boot ROM (limited subset of the Cisco IOS feature
  set)
• Cisco IOS (normal operations)
• To change the default start up mode of the
  router, the system administrator can change the
  configuration register setting

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Router Initialization

• A router initializes by loading the
• bootstrap
• operating system
• configuration file
• If the router cannot find a configuration file,
  it enters setup mode

Performs POST first (tests hardware)
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Router LED Indicators

• LED indicators to provide status information
• 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
  

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Examining Initial Router Bootup

• NVRAM invalid, possibly due to write erase
• router has not been configured yet or that the
  NVRAM has been erased
• The router must be configured and the
  configuration file saved to NVRAM

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Establishing a HyperTerminal Session

• To connect a terminal to the console port on the
  router
• Connect the terminal using the rollover cable and
  an RJ-45 to DB-9 or RJ-45 to DB-25 adapter
• Configure the terminal or PC terminal emulation
  software for 9600 baud, 8 data bits, no parity,
  1 stop bit, and no flow control

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RECAP of Router Access Levels

• For security purposes, the router has two levels
  of access to commands
• User EXEC mode Typical tasks include those that
  check the router status. In this mode, router
  configuration changes are not allowed
• Privileged EXEC mode Typical tasks include
  those that change the router configuration
• to make configuration changes, you must enter
  global configuration mode type config t)

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Router Configuration Modes

• The following are specific sub-modes that can be
  accessed from the global configuration mode
• Interface
• Subinterface
• Line
• Router
• Route-map
• disable command or exit returns user to the
  privileged EXEC mode from the global
  configuration mode
• Ctrl-Z returns user directly to the privileged
  EXEC mode from any sub-mode of global
  configuration.

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Help with the Router CLI

• To access help type a question mark (?)
• 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
• The caret symbol () indicates a syntax error in
  a command (The placement of the caret symbol
  shows where the possible problem is located)

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IOS Editing Functions
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IOS Command History

• The command history is enabled by default and the
  system records ten command lines in its history
  buffer
• The maximum number of commands is 256

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Introduction to Routers
THE END

• CCNA 2 v 3.0
• Module 2