Semester 2 Module 2 Introduction to Routers

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Semester 2 Module 2Introduction to Routers

• Yuda college of business
• James Chen
• ydjames_at_ydu.edu.tw

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Outline

• Operating Cisco IOS Software
• Starting a Router

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The purpose of Cisco IOS software

• 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.
• The Cisco IOS provides the following network
  services
• Basic routing and switching functions
• Reliable and secure access to networked resources
  
• Network scalability

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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
• A console uses a low speed serial connection
  directly from a computer or terminal to the
  console connection on the router.
• A dialup connection using a modem or null modem
  connected to the router AUX port.
• Telnet to the router.

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Router user interface modes 

• The IOS provides a command interpreter service
  known as the command executive (EXEC).
• As a security feature the Cisco IOS software
  separates the EXEC sessions into two access
  levels.
• user EXEC mode
• privileged EXEC mode (enable mode)

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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 gt"
  prompt

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Privileged EXEC mode

• The privileged EXEC mode accesses all router
  commands.
• This mode can be configured to require a password
  from the user before accessing it.
• 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.

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• To access the privileged EXEC level from the user
  EXEC level, enter the enable command at the gt
  prompt.
• If a password is configured, the router will then
  ask for that password.
• 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.

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Cisco IOS software features

• 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.

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• 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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• 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.

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Operation of Cisco IOS software

• The Cisco IOS devices have three distinct
  operating environments or modes
• ROM monitor
• Boot ROM
• Cisco IOS
• 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.

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ROM monitor

• 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.
• 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.

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Boot ROM

• 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.

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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.

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• To see the IOS image and version that is running,
  use the show version command, which also
  indicates the configuration register setting.
• The show flash command is used to verify that the
  system has sufficient memory to load a new Cisco
  IOS image.

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Outline

• Operating Cisco IOS Software
• Starting a Router

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Initial startup of Cisco routers

• A router initializes by 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).

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• The goal of the startup routines for Cisco IOS
  software is to start the router operations.
• To do this, the startup routines must accomplish
  the following
• Make sure that the router hardware is tested and
  functional.
• Find and load the Cisco IOS software.
• Find and apply the startup configuration file or
  enter the setup mode.

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• 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.

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• After the POST, the following events occur as the
  router initializes
• Step 1 The generic bootstrap loader in ROM
  executes.
• Step 2 The IOS can be found in several places.
• Step 3 The operating system image is loaded.

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• Step 4 The configuration file saved in NVRAM is
  loaded into main memory and executed one line at
  a time.
• Step 5 If no valid configuration file exists in
  NVRAM, the operating system searches for an
  available TFTP server. If no TFTP server is
  found, the setup dialog is initiated.

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• 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.

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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.

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Examining the initial router bootup

• The examples show information and messages
  displayed during initial bootup.
• This information will vary, depending on the
  interfaces in the router and the Cisco IOS
  release.

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Establishing a HyperTerminal session

• All Cisco routers include a TIA/EIA-232
  asynchronous serial console port (RJ-45).
• To connect a PC running terminal emulation
  software to the console port, use the RJ-45 to
  RJ-45 rollover cable with the female RJ-45 to
  DB-9 adapter.
• The default parameters for the console port are
  9600 baud, 8 data bits, no parity, 1 stop bit,
  and no flow control.

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Logging into the router

• To configure Cisco routers, the router user
  interface must be accessed with a terminal or by
  remote access.
• The user EXEC mode prompt is displayed upon login
  to a router.
• At the "gt" prompt, type enable.
• At the password prompt, enter the password that
  has been set with the enable secret command.

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• Two commands can be used to set a password used
  to access privileged EXEC mode enable password
  and enable secret.
• If both commands are used, the enable secret
  command takes precedence.
• The global configuration mode can only be
  accessed from the privileged EXEC mode.

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• The following are specific modes that can also be
  accessed from the global configuration mode
• Interface
• Subinterface
• Line
• Router
• Route-map
• 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 may also be used to return directly to the
  privileged EXEC mode from any sub-mode of global
  configuration.

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Keyboard help in the 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.

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Enhanced editing commands
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Router command history
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Troubleshooting command line errors

• The "" symbol appears at the point in the
  command string where an incorrect command,
  keyword, or argument was entered.

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The show version command

• Figure shows the following information 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