Transcript Chapter 3

Semester 2 Module 3
Configuring a Router
Andres, Wen-Yuan Liao
Department of Computer Science and Engineering
De Lin Institute of Technology
[email protected]
http://www.cse.dlit.edu.tw/~andres
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Outline
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Configuring a Router
Finishing the Configuration
CLI command modes
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All command-line interface (CLI) configuration
changes to a Cisco router are made from the
global configuration mode.
Other more specific modes are entered
depending upon the configuration change that is
required, but these specific modes are all
subsets of the global configuration mode.
Note: The prompt changes to indicate that the
router is now in global configuration mode.
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These are just a few of the modes that can
be entered from global configuration mode:
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Interface mode
Line mode
Router mode
Subinterface mode
Controller mode
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Typing exit from one of these specific
configuration modes will return the router
to global configuration mode.
Pressing Ctrl-Z leaves the configuration
modes completely and returns the router
to privileged EXEC mode.
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Configuring a router name
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A router should be given a unique name as one
of the first configuration tasks.
This task is accomplished in global configuration
mode using the following commands:
Router(config)#hostname Tokyo
Tokyo(config)#
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As soon as the Enter key is pressed, the prompt
changes from the default host name (Router) to
the newly configured host name, which is Tokyo
in the example.
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Configuring router passwords
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Passwords
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virtual terminal lines
console line
privileged EXEC mode
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The following commands are used to set
an optional but recommended password
on the console line:
Router(config)#line console 0
Router(config-line)#password <password>
Router(config-line)#login
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The following commands are used to set
the password on the VTY lines:
Router(config)#line vty 0 4
Router(config-line)#password <password>
Router(config-line)#login
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The enable password and the enable secret are
used to restrict access to the privileged EXEC
mode.
The enable password is only used if the enable
secret has not been set.
It is recommended that the enable secret always
be set and used because it is encrypted while
the enable password is not encrypted.
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These are the commands that are used to
set the enable passwords:
Router(config)#enable password <password>
Router(config)#enable secret <password>
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This command is used to encrypt passwords in
configuration output:
Router(config)#service password-encryption
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The service password-encryption command
applies a weak encryption to all unencrypted
passwords.
The enable secret <password> command uses
a strong MD5 algorithm for encryption.
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Examining the show commands
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There are many show commands that can
be used to examine the contents of files in
the router and for troubleshooting.
In both privileged EXEC and user EXEC
modes, the command show ? provides a
list of available show commands.
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show interfaces – Displays all the statistics for
all the interfaces on the router. To view the
statistics for a specific interface, enter the show
interfaces command followed by the specific
interface and port number. For example:
Router#show interfaces serial 0/1
show controllers serial – Displays informationspecific to the interface hardware
 show clock – Shows the time set in the router
 show hosts – Displays a cached list of host
names and addresses
 show users – Displays all users who are
17 connected to the router
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show history – Displays a history of commands that
have been entered
 show flash – Displays information about flash memory
and what IOS files are stored there
 show version – Displays information about the router
and the IOS that is running in RAM
 show ARP – Displays the ARP table of the router
 show protocol – Displays the global and interface
specific status of any configured Layer 3 protocols
 show startup-configuration – Displays the saved
configuration located in NVRAM
 show running-configuration – Displays the
18 configuration currently running in RAM
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Configuring a serial interface
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To configure a serial interface follow these
steps:
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Enter global configuration mode
Enter interface mode
Specify the interface address and subnet
mask
Set clock rate if a DCE cable is connected.
Skip this step if a DTE cable is connected.
Turn on the interface
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Configure the IP address using the
following commands:
Router(config)#interface serial 0/0
Router(config-if)#ip address <ip address>
<netmask>
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Serial interfaces require a clock signal to
control the timing of the communications.
In most environments, a DCE device such
as a CSU will provide the clock.
By default, Cisco routers are DTE devices
but they can be configured as DCE
devices.
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The clock is enabled and speed is
specified with the clock rate command.
The available clock rates in bits per
second are: 1200, 2400, 9600, 19200,
38400, 56000, 64000, 72000, 125000,
148000, 500000, 800000, 1000000,
1300000, 2000000, or 4000000.
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By default, interfaces are turned off, or
disabled.
To turn on or enable an interface, the
command no shutdown is entered
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The commands for setting a clock rate and
enabling a serial interface are as follows:
Router(config)#interface serial 0/0
Router(config-if)#clock rate 56000
Router(config-if)#no shutdown
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Executing adds, moves, and
changes
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If a configuration requires modification, go to the
appropriate mode and enter the proper
command.
To verify changes, use the show runningconfig command.
To save the configuration variables to the startup
configuration file in NVRAM, enter the following
command at the privileged EXEC prompt:
Router#copy running-config startup-config
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Configuring an Ethernet interface
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To configure an Ethernet interface follow these
steps:
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Enter global configuration mode
Enter interface configuration mode
Specify the interface address and subnet mask
Enable the interface
By default, interfaces are turned off, or disabled.
To turn on or enable an interface, the command
no shutdown is entered.
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Outline
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Configuring a Router
Finishing the Configuration
Importance of configuration
standards
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It is important for standards to be
developed for configuration files within an
organization.
This allows control of the number of
configuration files that must be maintained,
how the files are stored, and where the
files are stored.
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A standard is a set of rules or procedures
that are either widely used or officially
specified.
Without standards in an organization, a
network could be in chaos should an
interruption in service occur.
Interface descriptions
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A description of an interface can help a
network user remember specific
information about the interface, such as
what network the interface services.
The description is meant solely as a
comment about the interface.
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Configuring interface description
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Procedure steps:
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Enter global configuration mode by entering the
command configure terminal.
Enter specific interface mode (for example interface
Ethernet 0) interface ethernet 0.
Enter the command description followed by the
information that is to be displayed. For example, XYZ
Network, Building 18.
Exit interface mode back to privileged EXEC mode by
using the command ctrl-Z.
Save the configuration changes to NVRAM by using
the command copy running-config startup-config.
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Login banners
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A login banner is a message that is displayed at
login and is useful for conveying messages that
affect all network users, such as notices of
impending system shutdowns.
Login banners can be seen by anyone.
Therefore, careful attention should be used in
the wording of a banner message. “Welcome” is
an invitation for anyone to enter a router and is
probably not an appropriate message.
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Configuring message-of-the-day
(MOTD)
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A message-of-the-day (MOTD) banner can be
displayed on all connected terminals.
Enter global configuration mode to configure a
message-of-the-day (MOTD) banner.
Use the banner motd command, followed by a
space and a delimiting character, such as the
pound sign (#).
Add a message-of-the-day (MOTD) followed by
a space and the delimiting character again.
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Follow these steps to create and display
a message-of-the-day:
1.
2.
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Enter global configuration mode by using
the command configure terminal.
Enter the command banner motd # The
message of the day goes here #.
Save changes by issuing the command
copy running-config startup-config.
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Host name resolution
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Host name resolution is the process that a
computer system uses to associate a host
name with an IP address.
A list of host names and their associated
IP addresses is called a host table.
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Configuring host tables
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The procedure to configure the host
table:
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Enter global configuration mode in the router.
Enter the command ip host followed by the
name of the router and all IP addresses
associated with the interfaces on each
router.
Continue entering until all routers in the
network are entered.
Save the configuration to NVRAM.
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Configuration backup and
documentation
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Management of device configuration includes
the following tasks:
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Listing and comparing configuration files on running
devices
Storage of configuration files on network servers
Performing software installations and upgrades
Configuration files should be stored as backup
files in the event of a problem.
 Configuration files can be stored on a network
server, on a TFTP server, or on a disk stored in
a safe place.
 Documentation should be included with this
46 offline information.
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Copying, editing, and pasting
configurations
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The copy running-config tftp command can be
used to store the current configuration on a
network TFTP server.
To do so, complete the following tasks:
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Step 1 Enter the copy running-config tftp command.
Step 2 Enter the IP address of the host where the
configuration file will be stored.
Step 3 Enter the name to assign to the configuration
file.
Step 4 Confirm the choices by answering yes each
time.
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A configuration file stored on one of the network
servers can be used to configure a router.
To do so, complete the following tasks:
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Enter configuration mode by entering the copy tftp
running-config command
At the system prompt, select a host or network
configuration file.
At the system prompt, enter the name of the
configuration file or accept the default name.
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