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CHAPTER 3

Configuring a Router
This chapter provides information and commands concerning the following topics:
• Configuring a router, specifically:
— Names
— Passwords
— MOTD banners
— IP host tables
— Saving and erasing your configurations
• show commands to verify the router configurations

Router Modes
Router>

User mode

Router#

Privileged mode

Router(config)#

Globalconfiguration mode

Router(config-if)#

Interface mode

Router(config-subif)#

Subinterface mode

Router(config-line)#

Line mode

Router(config-router)#

Router configuration mode

TIP: There are other modes than these. Not all commands work in all
modes. Be careful. If you type in a command that you know is correct—show
run, for example—and you get an error, make sure that youare in the correct
mode.

PART II CCNA 2

— Interfaces

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Configuring Passwords

Global Configuration Mode
Router>

Can see config, but not change

Router#

Can see config and move to make
changes

Router#config t

Moves to global config mode

Router(config)#

This prompt indicates that you can
start making changes

Configuring a Router Name
This command works on bothrouters and switches.
h
Router(config)#hostname Cisco

Name can be any word you choose

Cisco(config)#

Configuring Passwords
Works on both routers and switches.
e
Router(config)#enable password cisco

Sets enable password

e
Router(config)#enable secret class

Sets enable secret password

l
Router(config)#line con 0

Enters console-line mode

p
Router(config-line)#passwordconsole

Sets console-line mode password to
console

l
Router(config-line)#login

Enables password checking at login

l
Router(config)#line vty 0 4

Enters vty line mode for all 5 vty
lines

p
Router(config-line)#password telnet

Sets vty password to telnet

l
Router(config-line)#login

Enables password checking at login

show Commands

19

l
Router(config)#line aux0

Enters auxiliary line mode

p
Router(config-line)#password backdoor

Sets auxiliary line mode password to
backdoor

l
Router(config-line)#login

Enables password checking at login

CAUTION: Enable secret password is encrypted by default. Enable password is
not. For this reason, recommended practice is that you never use the enable
password. Use only the enable secret passwordin a router configuration.

CAUTION: You cannot set both enable secret and enable password to the same
password. Doing so defeats the use of encryption.

Password Encryption
s
Router(config)#service passwordencryption

Applies a weak encryption to
passwords

e
Router(config)#enable password cisco

Sets enable password to cisco

l
Router(config)#line con 0

…

pRouter(config-line)#password Cisco

Continue setting passwords as above
…

n
Router(config)#no service passwordencryption

Turns off password encryption

CAUTION: If you have turned on service password encryption, used it, and then
turned it off, any passwords that you have encrypted will stay encrypted. New
passwords will remain unencrypted

show Commands
s
Router#show ?

Lists all showcommands available

s
Router#show interfaces

Displays statistics for all interfaces

s
Router#show interface serial 0

Displays statistics for a specific
interface, in this case Serial 0

s
Router#show ip interface brief

Displays a summary of all
interfaces, including status and IP
address assigned

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Interface Names

s
Router#show controllers serial 0

Displays statisticsfor interface
hardware. Statistics display if the
clock rate is set and if the cable is
DCE, DTE, or not attached

s
Router#show clock

Displays time set on device

s
Router#show hosts

Displays local host-to-IP address
cache. These are the names and
addresses of hosts on the network to
which you can connect

s
Router#show users

Displays all users connected to
device

s...