2. Objectives
• Describe router elements
• Configure router passwords, identification, and
banner
• Use the context-sensitive help facility
• Use the command history and editing features
• Perform the initial router configuration
• Use show commands to display basic network
• operational features
• Describe router start-up sequence
• Establish connectivity from a host to the appropriate
• network device to perform configuration tasks
• In accordance with open standards, interconnect
• network devices
• Differentiate between routed and routing protocols
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3. Cisco Router IOS
The Cisco Internetwork Operating System (IOS) is the
kernel of Cisco routers and most switches.
Almost all Cisco routers run the same IOS, in contrast to
only about half of their switches.
The IOS was created to deliver network services and
enable networked applications.
You can access the Cisco IOS through the console port of
a router, from a modem into the Aux port, or even through
Telnet.
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4. Internal Components of a Cisco Router
In order to configure and troubleshoot a Cisco
internetwork, one needs to know the major components of
Cisco routers and understand what these components do.
The Router Boot Sequence
When a router boots up, it performs a series of steps, called
the boot sequence, to test the hardware and load the
necessary software.
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5. Managing Configuration Registers
All Cisco routers have a 16-bit software register, which is
written into NVRAM .
Understanding the Configuration
Register Bits
The 16 bits of the configuration register are read from 15 to
0, from left to right. The default configuration setting on
Cisco routers is 0x2102.
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6. Managing Configuration Registers contd..
Checking the Current Configuration Register
Value
You can see the current value of the configuration register by
using the show version command (sh version or show ver for
short),
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7. Managing Configuration Registers contd..
Changing the Configuration Register
One can change the configuration register value to
modify how the router boots and runs.
One can change the configuration register by using
the config-register command.
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8. Managing Configuration Registers contd..
Recovering Passwords
If you are locked out of a router because you forgot the
password, you can change the configuration register to help
you recover.
The default configuration register value is 0x2102, which
means that bit 6 is off.
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9. Managing Configuration Registers contd..
Interrupting the Router Boot Sequence
The first step is to boot the router and perform a break,
by pressing the Ctrl+Break key combination when using
HyperTerminal.
Changing the Configuration Register
You can change the configuration register by using the
config-register command. To turn on bit 6, use the
configuration register value 0x2142.
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10. Managing Configuration Registers contd..
Reloading the Router and Entering
Privileged Mode
At this point, you need to reset the router.
• From the 2600 series router, type reset.
• From the 2500 series router, type I (for initialize).
Viewing and Changing the Configuration
Although you cannot view the enable secret setting for the
password, you can change the password, by:
config t
enable secret rahul
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11. Managing Configuration Registers contd..
Resetting the Configuration Register and
Reloading the Router
After you are finished changing passwords, set the
configuration register back to the default value with the
config-register command.
config t
config-register 0x2102
Finally, save the new configuration with a copy running-config
startup-config and reload the router.
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12. Cisco Router User Interface
You can connect to a Cisco router to configure the router,
verify the configuration, and check statistics.
There are different ways to do this, but most often, the first
place you would connect to is the console port.
But you can also connect to a Cisco router through an
auxiliary port, which is really the same thing as a console
port so you can use it as one.
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13. Cisco Router User Interface contd..
Bringing Up a Router
When you first bring up a Cisco router, it will run a power-on
self-test (POST), and if that passes, it will then look for and
load the Cisco IOS from Flash memory, if a file is present.
Flash memory is an electronically erasable programmable
read-only memory [EEPROM]. The IOS then proceeds to
load and then look for a valid configuration – the startup-
config – that's stored by default in nonvolatile RAM
(NVRAM).
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14. Setup Mode
There are two options when using setup mode:
Basic Management and Extended Setup.
Basic Management setup configures only enough
connectivity for management of the system.
Command-Line Interface
The command-line interface (CLl) is really the best way to
configure a router.
Logging into the Router
After the interface status messages appear and you press
Enter, the Router> prompt will appear.
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15. Command-Line Interface contd..
Overview of Router Modes
To configure from a CLI, you can make global changes to
the router by typing configure terminal (or config t for short),
which puts you in global configuration mode and changes
what's known as the running-config.
CLI Prompts
It's really important that you understand the different
prompts you can find when configuring a router. Always
check your prompts before making any changes to a router's
configuration!
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16. Command-Line Interface contd..
Editing and Help Features
You can use the Cisco advanced editing features to help
you configure your router.
Real world Scenario
There are a couple of editing features that are used quite
often; some are not used as much, if at all. Understand that
Cisco didn't make these up; these are just old Unix
commands. However, Ctrl+A is really helpful to negate a
command.
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17. Command-Line Interface contd..
Gathering Basic Routing Information
The show version command will provide basic configuration
for the system hardware as well as the software version,
the names and sources of configuration files, and the boot
images.
Setting Passwords
There are five passwords used to secure your Cisco routers.
The first two passwords are used to set your enable
password, which is used to secure privileged mode. The
other three are used to configure a password when user
mode is accessed either through the console port, the
auxiliary port, or via Telnet.
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18. Command-Line Interface contd..
Encrypting Your Passwords
Only the enable secret password is encrypted by default,
you'll need to manually configure the user-mode and
enable passwords.
Banners
A good reason for having a banner is to add a security
notice to users dialing into your internetwork.
Router Interfaces
Interface configuration is one of the most important
configurations of the router, because without interfaces, a
router is totally useless.
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19. Command-Line Interface contd..
Bringing Up an Interface
You can turn an interface off with the interface command
shutdown, and turn it on with the no shutdown command.
Configuring an IP Address on an
Interface you don't have to use IP on your routers, it's
Even though
most often what people use. To configure IP addresses on
an interface, use the ip address command from interface
configuration mode .
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20. Command-Line Interface contd..
Serial Interface Commands
The interface will usually be attached to a CSU/DSU type of
device that provides clocking for the line. But if you have a
back-to-back, one end-the data communication equipment
(DCE) end of the cable-must provide clocking.
Hostnames
You can set the identity of the router with the host name
command. This is only locally significant, which means it
has no bearing on how the router performs name lookups or
how the router works on the internetwork.
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21. Command-Line Interface contd..
Descriptions
Setting descriptions on an interface is helpful to the
administrator and, like the hostname, only locally significant.
This is a helpful command because you can use it to keep
track of circuit numbers.
Real World Scenario
The interface description command is very helpful if, for
example, you have many administrators and no one can
remember where any interface is connected.
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22. Command-Line Interface contd..
Viewing and Saving Configurations
If you run through setup mode, you'll be asked if you want
to use the configuration you just created.
Verifying Your Configuration
Show running-config would be the best way to verify your
configuration, and show startup-config would be the best
way to verify the configuration that'll be used the next time
the router is reloaded.
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23. Using Telnet
Telnet is a virtual terminal protocol that is part of the TCP/IP
protocol suite. Telnet allows you to make connections to
remote devices, gather information, and run programs.
Telnetting into Multiple Devices
Simultaneously
If you telnet to a router or switch, you can end the
connection by typing exit at any time.
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24. Using Telnet contd..
Checking Telnet Connections
To see the connections made from your router to a remote
device, use the show sessions command.
Checking Telnet Users
You can list all active consoles and VTY ports in use on
your router with the show users command.
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25. Using Telnet contd..
Closing Telnet Sessions
You can end Telnet sessions a few different ways. Typing
exit or disconnect is probably the easiest and quickest.
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26. Resolving Hostnames
In order to use a hostname rather than an IP address to
connect to a remote device, the device that you are using
to make the connection must be able to translate the
hostname to an IP address.
Building a Host Table
A host table provides name resolution only on the router on
which it was built
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27. Resolving Hostnames contd..
Using DNS to Resolve Names
If you have many devices and don't want to create a host
table in each device, you can use a DNS server to resolve
hostnames.
Real World Scenario
If you have dozens of routers, then you don't want to build
a static host table on each router. You can build one table
on a DNS server.
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28. Checking Network Connectivity
You can use the ping and trace route commands to test
connectivity to remote devices.
Using the Ping Command
To see all the different protocols that you can use with ping,
use the ping ? Command.
Using the Traceroute Command
Traceroute (the traceroute command, or trace for short)
shows the path a packet takes to get to a remote device.
CMC Limited
