Editing Configuring a Router

All CLI configuration changes to a Cisco router are made from global configuration mode, which is sometimes called global config. Global config is the primary configuration mode.


=Configuring a Router=

A router should be given a unique name as one of the first configuration tasks
In order to accomplished this go to the global configuration mode with the following command: 

Router(config)#hostname Tokyo 
Tokyo(config)# 



==Configuring router passwords==

As a best practive restrict access to routers with a password.
Passwords should always be configured for virtual terminal (vty) lines and the console line. Passwords are also used to control access to privileged '''EXEC mode''' so that only authorized users may make changes to the configuration file. 



===Console Password===
 Router(Config)# line console 0
 Router(Config)# password cisco
 Router(Config)# login

===Virtual Terminal Password===
 Router(Config)# line vty 0 4 (when configuring telenet sessions)
 Router(Config)# password cisco
 Router(Config)# login

===Enable Password===
 Router(Config)# enable password SanFranciso
 Router(Config)# service password-encryption (to encrypt non  encrypted passwords)
 

The enable password used to restrict access to the privileged EXEC mode IF the enable secret has not been set. 

Sometimes it is undesirable for passwords to be shown in clear text in the output from the show '''running-config''' or show '''startup-config''' commands and a a best practice we should
used the "service password-encryption" command


===Password encryption=== 

 Router(Config)# enable secret <password> (encrypted password)

The enable secret commands is used to restrict access to the privileged EXEC mode
The enable secret command should be used because the enable secret command is encrypted

==Configuring Serial & Ethernet Interfaces==
To configure a serial interface either from the console or through a virtual terminal line follow these steps: 

#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.


The variable "TYPE" here is for serial, ethernet, fasethernet, token ring and others.

 Router(Config)# interface type port
 Router(Config)# interface type slot/port

Each Interface that has been configured with the above commands needs an IP Address and a Subnet mask. Configure the IP address with the following commands: 

 Router(config)#interface serial 0/0 
 Router(config-if)#ip address <ip address > <netmask > 

Serial interfaces require a clock signal to control the timing of the communications in most cases a DCE device such as a CSU/DSU will provide the clock. By default, Cisco routers are DTE devices but they can be configured as DCE devices. 

The clock is enabled and speed is specified with the clock rate command. Available clock rates are:
*1200
*2400
*9600
*19200
*38400
*56000
*64000
*72000

Some bit rates might not be available on certain serial interfaces. This depends on the capacity of each interface.

This commands is used to administratively turn off/on an interface
Command A will administratively turn off an interface
Command A will administratively turn on an interface

 A) Router(Config)#shutdown
 B) Router(Config)# no shutdown

By default, interfaces are turned off, or disabled. To turn on or enable an interface, the command no shutdown is entered. If an interface needs to be administratively disabled for maintenance or troubleshooting, the shutdown command used to turn off the interface.

The commands that are used to set a clock rate and enable a serial interface are as follows:

 Router(config)#interface serial 0/0 
 Router(config-if)#clock rate 56000 
 Router(config-if)#no shutdown