CCNA2 Chapter 2
Cisco IOS Software
Cisco’s operating system is called Cisco Internetwork Operating System (IOS)
IOS provides the following network services:
• basic routing and switching functions
• reliable and secure access to networked resources
• network scalability
Cisco IOS Software
Cisco IOS software uses a command-line interface (CLI) as the console environment.
This environment is accessible via:
• console session
Uses a low speed serial connection directly from PC to router
• AUX port
Dialup with a modem through AUX port. Don’t need the router to be connected to network services
• Telnet
Must have at least one interface configured with IP address, and virtual terminal sessions must be configured for login & password.
Access to Routers
The Cisco CLI uses a hierarchical structure, called modes.
The IOS provides a command interpreter service known as the command executive (EXEC).
For security reasons, Cisco routers have two access levels:
• user EXEC mode
Has limited number of basic monitoring commands.
This mode is identified by > (Example: Router>)
• privileged EXEC
Requires password
May require an user ID
Users can accesses all router commands
This mode is identified by # (Example: Router#)
Cisco IOS Software
Cisco IOS releases naming convention contain 3 parts:
• platform on which the image runs
• special features supported in the image
• where the image runs and whether it has been zipped or compressed
It is of the form: xxxx-yyyy-ww
• xxxx = Platform
• yyyy = Features
• ww = Format – where it executes
Cisco IOS Software
Before installing a new Cisco IOS software image on the router, check to see if the router meets the memory requirements.
Use the command: show version
Cisco IOS Software
• To find out amount of flash memory, use the command: show flash
Cisco IOS Software
show version command displays:
• 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 (how IOS is booted)
Router Commands
IOS version
Boot ROM version
Router up time
Last restart method
System image file & location
Configuration register setting
Number & type of interfaces on the router
•Platform
•Feature set
•Location to be used for loading the IOS
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
Cisco IOS has 3 distinct operating environments or modes:
• ROM monitor
Performs the bootstrap processProvides low-level functionality and diagnostics. Used for password recovery. Can NOT be accessed through any interface.
• Boot ROM
Only a limited subset of Cisco IOS features are available. One is allowed to write to flash memory & is used primarily to replace the Cisco IOS image stored in flash
• Cisco IOS
Needs the full IOS image as stored in flash
Cisco IOS Software
The major steps in initialization of a router are:
• Power up self test (POST)
• Bootstrap loader in ROM executes
• Locate and load the operating system
• Locate and load the configuration files
Initial Startup
• Bootstrap loader
Simple set of instructions that tests hardware and initializes the IOS
• Locate and load IOS (determined where by the configuration register stored in NVRAM (if indicates Flash, then looks for boot system comands; if none, the default is:)
• Flash• TFTP server• ROM
• locate and load configuration files
• NVRAM• TFTP server
• Console
If no TFTP server is found, then the setup dialog is initiated.
Initial Startup
• 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.
• Pressing the Enter key accepts 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– 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
Setup Mode
After the system initializes correctly, the LED to the right of the AUX port will become green. (2600 light is in the front)
Initial Startup
The default parameters for the console port are:
• console port: 9600 baud• data bits: 8• no parity• 1 stop bit• no flow control
HyperTerminal
• User (User EXEC) mode Router>
• Privilege mode Router#
• Global configuration mode Router# config t
Only accessible from the privilege mode.
From this mode one can access:
• interfaces
• sub interfaces
• line
• router
• router-map
Router Modes
?
Ctrl-A – moves to the beginning of the command line
Esc-B – move back one word
Ctrl-B – move back one character (left arrow)
Ctrl-E – move to the end of the command line
Ctrl-F – move forward one character (right arrow)
Esc-F – move forward one word
Ctrl-P – recalls last or previous command (up arrow)
Ctrl-N – recalls most recent command (down arrow)
<Tab> - complete the entry
Router HELP commands
Using the Help System
Router HELP commands
Maximum number of commands in the history buffer is 256
Router Command History