Section 4: The Cisco IOS Operating System

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17. Introduction

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18. Cisco Operating Systems

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Not required for the Exam

  • Cisco started with Routers in 1984
  • IOS is the OS
  • Original OS was CatOS

NEW Operating Systems

  • NX-OS: Cisco Nexus and MDS data center swietch products
  • IOS-XR: NCS, CRS, ASR9000 and XR12000 series routers
  • ISO-XE: ASR1000 series routers
  • Command line for these are nearly identical to IOS

19. Making the initial connection to a Cisco device

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  • For day to day management, you’ll use SSH (Secure Shell) to connect to the management IP
  • For enterprise networks, secure login will typically be enforced through integration with a centralised AAA (Authentication, Authorization and Accounting) server.
  • Cisco devices do not have a default IP, so one needs to be setup.
  • To setup the initial IP, you’ll need to console the device
    • Requires a special console cable.
    • Connects to your serial port and to the devices with an RJ-45 connector
    • Since most computers do not include a serial port anymore, you’ll need a USB to Serial port adapter.
      • This will require a driver before it will work
    • Newer Cisco devices now come with a special USB to Mini USB cable.
      • You’ll still need a drive

Connecting with Putty

  • Select ‘Serial’ connection
  • Speed: 9600 baud
  • Serial Line: Com1 (or whatever com port you’re using.)

Why use the Console Cable

  • Initial configuration
  • Required if the devices IP becomes unresponsive
    • Stolen?
  • Can be used to troubleshoot the boot process.
    • You can view the device booting from the console connection
    • You cannot do this via SSH since the system must be booted prior to connecting
  • Can be used for Out of Band Management
    • This is where you use a different path (other than production network) to connect to the device for management.
    • if you have an issue with the Production network, you can still access the router or switch
      • This is usually accomplished using a Terminal Server that is often another router.

20. Navigating the Cisco IOS Operating System Part 1

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Initial Boot:

Would you like to enter the initial configuration dialog? [yes/no]: no
Would you like to terminat autoinstall? [yes/no] : yes

After boot, you’ll be in User Exec mode.

User Exec mode

Router>
  • Designated by ‘Hostname>’
  • Very limited commands available
  • Press ‘?’ to see a list of available commands
  • —More— means there are additional commands to see
    • [Enter] Scroll line by line
    • [ _ ] (Space) scroll page by page.
      • Recommended to set Putty scroll back to 2000
    • Press [Ctrl] [C] to stop scrolling

Privileged Exec mode

Router>enable
Router#
  • aka ‘The Enable prompt’
  • Type ‘enable’ to access
    • Type ‘disable’ to return to User Exec mode
  • Designated by ‘Hostname#’

Using command abbreviation

  • Enter the first few characters of the command.  If a unique match is found, you can just use it.
    • enable = ‘en’
  • if a unique command is not found:
    • ex: ‘di’
    • Ambiguous command: ‘di’
    • Press ‘?’ to see a list of possible matching commands
    • Continue typing until you’re reached a unique string that can only apply to the command you’re looking for.
  • To finds options for a specific command
    • Type the command (or unique abbreviation) [ _ ] [ ? ]
      • show ?
  • press [Tab] to auto complete a command.
  • If the list of commands ends with <cr> (Carriage Return) any other commands are optional.

Difference between ‘show’ and ‘debug’

  • Show will show the current state as you pressed [Enter]
  • Debug will continue to update as changes are encountered.

Global Configuration mode

Router configure terminal
Router(config)#
  • Abbreviation: ‘conf t’

21. Navigating the Cisco IOS Operating System Part 2

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Command History

[Ctrl] buttons are a bit messed up with minicom usb adaptor!

  • [ UpArrow ] – Previous command
    • Only shows commands for the current ‘exec’ mode.
  • [ Ctrl ] [A] – Start of the line
  • [ Ctrl ] [Z] – End of line

To run Privilege Exec commands at the Global Configuration mode

  • do (rest of command)
    • do show ip interface brief

Global Configuration level is used to configure items globally.  To edit specific items, you must first enter their mode…

Router(config)#interface fastethernet 0/0
Router(config-if)#

To return back to Global Config level

  • exit
Router(config-if)#exit
Router(config)#exit
Router#exit
Router>

To drop all the way back to the Privileged Exec mode

  • end
Router(config-if)#end
Router#

Most Common Commands

show ip interface brief

  • Shows all interfaces on the router
  • State of the interface (up or down)
  • IP address configured on the interface.

show running-config

  • Shows the entire configuration on the router
  • Several pages of data.

There are filters to only show specific sections of the running config.

show run int fast 0/0

  • only shows the config for Interface FastEthernet 0/0

Reg Ex

  • show run | begin hostname
    • starts from the first line that has hostname
  • show run | include host
    • shows all lines that include the word host
    • show run | include Host
      • Fails!  This is case sensitive!!
  • show run | exclude interface
    • show all lines excluding interface

show startup-config

  • Shows the configuration loaded at boot time.
  • Changes to the running config must be saved here, or they will all be lost on next reboot.

copy running-config startup-config

  • Copies the running config to the startup configuration.

copy run flash:<filename>

  • Copies the running config to flash disk space.

show flash

  • Displays files on the flash drive.

reload

  • Reboot the router

22. Cisco IOS Configuration Management

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Configuring the Router

  • Any changes made go into effect immediately and are recorded in the running-config.
  • These changes are NOT saved to the start up config unless you explicitly copy them there.
Router>enable
Router#configure terminal
Router(config)#

Set the hostname

Router(config)#hostname r1
r1(config)#

copy running-config startup-config

  • Copies the running config to the startup configuration.

copy run flash:<filename>

  • Copies the running config to flash disk space.

show flash

  • Displays files on the flash drive.

To restore the running config / startup config from the flash backup

  • Erase the startup config
    • #erase start
  • Copy the back up to the new startup
    • copy flash:<filename> startup-config

File Storage Locations

  • IOS is stored in Flash
  • Startup Config in NVRAM
    • Persistent across reboots
  • Running Config in RAM
    • Loaded from the running config during boot

23. Lab Exercises

04 The IOS Operating System – Lab Exercises

 

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