Module 2: Introduction to Routers

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Module 2 Introduction to Routers

• Semester 2 Version 3.0

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The purpose of Cisco IOS Software

• 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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2 Router user interface

• The Cisco IOS software uses a command-line
  interface (CLI) as the traditional console
  environment.
• One way to access the CLI is through a console
  session. A console uses a low speed serial
  connection directly from a computer (serial
  connection) 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.

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Router user interface modes

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

• 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

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• 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.
• Use the show version command on the Cisco device
  to check the current image and available flash.

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Before installing a new Cisco IOS software image

• Check to see if the router meets the memory
  requirements for that image
• To see the amount of RAM, issue the show version
  command
• cisco 1721 (68380) processor (revision C) with
  3584K/512K bytes of memory
• This line shows how much main and shared memory
  is installed in the router. Some platforms use a
  fraction of DRAM as shared memory. The memory
  requirements take this into account, so both
  numbers have to be added together to find the
  amount of DRAM installed on the router.

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show flash command

• Shows the amount of flash memory
• LabAshow flash ltoutput omittedgt15998976
  bytes total (10889728 bytes free)
• Displays all of the Cisco IOS image files on a
  router

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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.

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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.
• 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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ROM monitor mode

• Tasks performed in the ROM monitor mode include
• Changing the registry settings
• Replacing the Cisco IOS images files

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IOS image and version

• 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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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).
• The goal of the startup routines for Cisco IOS
  software is to start the router operations.
• Make sure that the router hardware is tested and
  functional. (check hardware, load bootstrap)
• Find and load the Cisco IOS software.
• Find and apply the startup configuration file or
  enter the setup mode.
• A router looks in NVRAM for boot system statements

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• When a Cisco router powers up, it performs a
  power-on self test (POST).
• After the POST, the following events occur as the
  router initializes
• Step 1The generic bootstrap loader in ROM
  executes.
• Step 2The boot field of the configuration
  register determines the location to be used in
  loading the IOS.
• Step 3The operating system image is loaded. When
  the IOS is loaded and operational, a listing of
  the available hardware and software components is
  output to the console terminal screen.
• Step 4The configuration file saved in NVRAM is
  loaded into main memory and executed one line at
  a time.
• Step 5If 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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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.
• A router enters setup mode
• After issuing the command Routersetup
• During the initial configuration of a router
• After deleting the backup configuration and
  reloading the router

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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 statement NVRAM invalid, possibly due to
  write erase, tells the user that this router has
  not been configured yet or that the NVRAM has
  been erased.
• The factory-default setting for the configuration
  register is 0x2102, which indicates that the
  router should attempt to load a Cisco IOS image
  from flash memory.
• Default sequence for loading the IOS
• FLASH
• TFTP
• ROM

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Configuration file

• Default sequence for loading
• NVRAM
• TFTP
• Console

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Establishing a HyperTerminal session

• All Cisco routers include a TIA/EIA-232
  asynchronous serial console port (RJ-45).
• A console terminal is an ASCII terminal or PC
  running terminal emulation software such as
  HyperTerminal.
• 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.

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Default parameters for the console port

• 9600 baud
• 8 data bits
• no parity
• 1 stop bit
• no flow control
• The console port does not support hardware flow
  control.

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To connect a terminal to the console port on the
router

• 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.
• 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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Logging into the router

• 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 access the full set of commands, privileged
  EXEC mode must be entered. 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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enable password and enable secret

• 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.

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• Once the login steps have been completed, the
  prompt changes to a "" indicating the privileged
  EXEC mode has been entered.
• The global configuration mode can only be
  accessed from the privileged EXEC mode. The
  following are specific modes that can also be
  accessed from the global configuration mode
  LabA(config)
• 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.
• The screen displays many lines at one time. 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.

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Enhanced editing commands

• To disable enhanced editing mode, type terminal
  no editing at the privileged EXEC mode prompt.
• To scroll back, press Ctrl-B or the left arrow
  key repeatedly until the beginning of the command
  entry is reached. Ctrl-A will return a user
  directly to the beginning of the line.
• The dollar sign () indicates that the line has
  been scrolled to the left.
• Ctrl-Z is a command used to back out of
  configuration mode.

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• Ctrl-A Moves to the beginning of the command
  line
• Esc-B Moves back one word
• Ctrl-B or left arrow Moves back one character
• Ctrl-E Move to the end of the command line
• Ctrl-F or right arrow Moves forward one
  character
• Esc-FMoves forward one word

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Router command history

• 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.
• Use the terminal history size or the history size
  command to change default.
• The maximum number of commands is 256.

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• 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.
• Press Ctrl-N or the down arrow key repeatedly to
  recall successively more recent commands.
• Press the Tab key, and the interface will finish
  the entry.

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Troubleshooting command line errors

• 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.
• To list the correct syntax, enter the command up
  to the point where the error occurred and then
  enter a question mark (?)

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The show version command

• The show version command displays information
  about the Cisco IOS software version that is
  currently running on the router. This includes
  the configuration register and the boot field
  settings and amount of RAM on the router.
• IOS version and descriptive information
• Bootstrap ROM version
• Boot ROM version
• Router up time
• Last restart method
• System image file and location
• The number and types of interfaces on the router
• Configuration register setting
• Use the show version command to identify router
  IOS image and boot source.

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THE

• END