Transcript Document

Semester 2 Module 2
Introduction to Routers
Yuda college of business
James Chen
[email protected]
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Outline
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Operating Cisco IOS Software
Starting a Router
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The purpose of Cisco IOS software
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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:
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Basic routing and switching functions
Reliable and secure access to networked resources
Network scalability
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Router user interface
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The Cisco IOS software uses a command-line
interface (CLI) as the traditional console
environment.
This environment is accessible through several
methods
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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
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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.
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user EXEC mode
privileged EXEC mode (enable mode)
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User EXEC mode
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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 “>"
prompt
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Privileged EXEC mode
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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 “>”
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
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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:
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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
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The Cisco IOS devices have three distinct operating
environments or modes:
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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
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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
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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
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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
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Operating Cisco IOS Software
Starting a Router
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Initial startup of Cisco routers
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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:
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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:
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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
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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
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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
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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
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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 ">" 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 submode of global configuration.
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Keyboard help in the router
CLI
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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
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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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The show version command
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Figure shows the following information from the
show version command:
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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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