CCNA 2 v3.1 Module 2
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CCNA 2
Module 2
Introduction to Routers
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Cisco IOS
• Cisco Internetwork Operating System is the
software that controls routing and switching
functions of internetworking devices
• Network services provided by Cisco IOS :
Basic routing and switching functions
Reliable and secure access to networked resources
Network scalability
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User Router Interface
• Cisco IOS software uses a command-line
interface (CLI)
• This environment is accessible through several
methods.
Console session
Uses a low speed serial connection directly from a
computer or terminal to the console connection on
the router
No initial configuration necessary
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Dialup connection:
Using a modem or null modem connected to
the router AUX port.
No initial configuration necessary
Telnet session:
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
• CLI uses a hierarchical structure.
• Entry into different modes to accomplish
tasks
E.g., To configure a router interface, the user must
enter interface configuration mode.
• Command executive (EXEC): Validates and
executes the entered commands.
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•
IOS software separates the EXEC sessions
into two access levels:
User EXEC mode
Privileged EXEC mode (enable)
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User EXEC mode (view only)
Limited number of basic monitoring commands
To check and view the router status
Cannot change the configuration of the router
Prompt >
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• Privileged EXEC mode (enable mode)
Accesses all router commands
Configuration and management
To ensure authorized users access this mode
Configured it to require a password from the
user before accessing it & User ID
Provides access to
Global configuration mode and others
Prompt #
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Type enable to enter privileged exec mode
Type disable to enter privileged exec mode
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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IOS Naming Conventions
Platform (Hardware): C1005
Features: “b”, Appletalk
40 = 40 bit encryption
Format: F = Flash, M = RAM
Compression: Z = Zip compressed
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• Consideration when selecting a new IOS image
Compatibility with the router flash and RAM memory
i.e., is there enough space
To find this information use show version
• router#show version
Displays the amount of available RAM
…cisco 1721 (68380) processor (revision C) with 3584K/512K
bytes of memory.
3584k main memory
512k shared memory
• router#show flash
Displays the amount of flash memory
…15998976 bytes total (10889728 bytes free
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Operation of Cisco IOS Software
•
The startup process of the router
normally loads into RAM and executes
one of three operating environments/
modes.
ROM monitor
Boot ROM
Cisco IOS
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Systems administrator uses the
configuration register setting to control
the default start up mode for the router
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• ROM Monitor:
provides low-level functionality and diagnostics
used to
recover from system failures
recover a lost password
Can only be accessed by direct, physical connection
through the console port
Prompt: ROMMON>
• Boot ROM :
Prompt: Router(boot)>
Offers only limited IOS features
Used for flash image updates
copy tftp flash
copies an IOS image stored on a TFTP server into the
flash memory of the router
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• Cisco IOS
Normal operating mode
Usually stored in Flash but run from RAM
Prompt: router>
• show version
Displays
IOS image and version
Configuration register setting
Amount of available RAM
• show flash
Displays the amount of flash memory
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
If the router cannot find a configuration file, it enters
“setup mode”. It is a basic configuration
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Startup routines must accomplish 3 things
Make sure that the router hardware is tested and
functional.
Find and load the Cisco IOS software
Flash, TFTP Server, ROM
Find and apply the startup configuration file or enter
the setup mode
NVRAM, TFTP Server, Console
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1. Powers up
Router
Startup Sequence
2. Performs a power-on self test (POST)
Executes diagnostics from ROM to check all hardware modules
This verifies basic operation of CPU, memory, network interface
ports
3. Software initialization
The boot field of the configuration register determines the location
to be used in loading the IOS.
Flash (0X2102), TFTP Server, ROM
IOS Software is loaded
List of hardware and software is displayed on console screen
4. If valid configuration file exists
Configuration file from NVRAM is loaded into main memory
start routing processes, supply addresses for interfaces
5. If no valid configuration file exists
Operating system searches for TFTP server
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Setup Mode
• Entered only if configuration file cannot be
found in NVRAM or TFTP
• Permits administrator to enter minimal router
configurations
• Default answers appear in [ ]
• Press Enter to use these defaults
• Press Ctrl-C at any time
to terminate the process(setup mode)
all interfaces will be administratively shutdown
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Router LED indicators
• An interface LED indicates the activity of the
corresponding interface.
A green OK LED indicates system is initialized correctly
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Examining the initial router bootup Output
Output indicates a problem with the “NVRAM”. It
could be “Write erased”
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Router Output Tells
• Bootstrap version
• IOS version the router
• Router model
• Processor
• Number of interfaces
• Types of interfaces
• Amount of NVRAM
• Amount of flash memory
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Logging into the router
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• When entering the Privilaged exec mode if the
password: prompt is displayed, enter the
password that has been set
• Password commands to access privileged
EXEC mode
Router(config)# Enable password <password>
Not encrypted
Router(config)#Enable secret <password>
Encrypted
Cannot be the same as enable password
Takes precedence over enable password
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• From the Privileged mode you can enter the
“Global Mode” & can configure the
following;
Interface
Subinterface
Line
Router
Route-map
• To return to the privileged mode type Ctrl Z.
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Keyboard help in the router CLI
• Typing a question mark (?) displays a handy list of available
commands. (user or privileged modes)
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• “?” can also be used to complete incomplete
commands
Eg .. Setting the router clock
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• The "^" symbol appears at the point in the
command string where an incorrect
command, keyword, or argument was
entered.
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Enhanced editing commands
“$” sign indicates that the command has
scrolled onto the next line.
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Router command history
The maximum number of commands held is 256.
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The show version command
• 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
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