Content Overview Configuring a router to perform complex internetworking tasks can be challenging. However, the beginning procedures for configuring a router are not difficult at all. If these procedures and the steps for moving between the various modes of the router are practiced, the more complex configurations will be much less daunting. This module introduces the basic configuration modes of the router and provides opportunities to practice simple configurations. A clear, easy to understand router configuration that is backed up regularly should be a goal of all network administrators. The Cisco IOS provides the administrator several tools to add information to the configuration file for documentation purposes. Just as a competent programmer provides documentation for each programming step, a network administrator must provide as much information as possible in the event that another person must assume responsibility for the network. Students completing this module should be able to:
Content 3.1 Configuring a Router 3.1.1 CLI command modes 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. Global configuration mode commands are used in a router to apply configuration statements that affect the system as a whole. The following command moves the router into global configuration mode and allows entry of commands from the terminal: Note: The prompt changes to indicate that the router is now in global configuration mode. Router#configure terminal
Router(config)# Global configuration mode, often shortened to global config, is the primary configuration mode. These are just a few of the modes that can be entered from global configuration mode: When these specific modes are entered, the router prompt changes to indicate the current configuration mode. Any configuration changes that are made will apply only to the interfaces or processes covered by the particular mode. 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. Web Links Cisco IOS Interface Command Reference, Release 12.1 http://www.cisco.com/en/US/ products/sw/ iosswrel/ ps1831/ products_command_reference_ book09186a00800880d1.html
Content 3.1 Configuring a Router 3.1.2 Configuring a router name 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)# 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. Lab Activity Lab Exercise: Command Modes and Router Identification This lab is to identify basic router modes of user EXEC and privileged EXEC and to use commands to enter specific modes. Web Links Basic System Management Commands http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/products_command_reference_ chapter09186a00800ca748.html#1018259
Content 3.1 Configuring a Router 3.1.3 Configuring router passwords Passwords restrict access to routers. Passwords should always be configured for virtual terminal 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.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 A password must be set on one or more of the virtual terminal (VTY) lines for users to gain remote access to the router using Telnet. Typically Cisco routers support five VTY lines numbered 0 through 4, although different hardware platforms support different numbers on VTY connections. Often the same password is used for all lines but sometimes one line is set uniquely to provide a fall-back entry to the router if the other four connections are in use. 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 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. These are the commands that are used to set the enable passwords: Router(config)#enable password <password>
Router(config)#enable secret <password> 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. This command is used to encrypt passwords in configuration output: Router(config)#service password-encryption 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. Lab Activity Lab Exercise: Configuring Router Passwords This lab is to configure a password for console login to user mode and configure a password for virtual terminal (Telnet) sessions. Lab Activity e-Lab Activity: Configuring Router Passwords In this lab, the student will configure passwords for the console, virtual terminals, and a secret password. Lab Activity e-Lab Activity: Command-line Interface Command Modes In this lab, the students will learn to enter some of the most common modes the router supports. Web Links Passwords and Privileges Commands http://www.cisco.com/en/US/products/sw/ iosswrel/ps1835/products_command_reference_ chapter09186a00800ca7cd.html#1017603
Content 3.1 Configuring a Router 3.1.4 Examining the show commands 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. The list is considerably longer in privileged EXEC mode than it is in user EXEC mode. Router#show interfaces serial 0/1