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Depending on the feature being used, there are different configuration modes when working with
Cisco IOS Software. Figure 1-1 shows the various Cisco IOS configuration modes employed in
this text.
The first method of configuration on a Cisco device is the setup utility, which lets you create a
basic initial configuration. For more complex and specific configurations, you can use the CLI to
enter terminal configuration mode.
Cisco IOS CLI Functions 5
Figure 1-1 Cisco IOS Configuration Modes
From privileged EXEC mode, you can enter global configuration mode using the configure
terminal command. From global configuration mode, you can access specific configuration
modes, which include, but are not limited to, the following:
■ Interface: Supports commands that configure operations on a per-interface basis
■ Subinterface: Supports commands that configure multiple virtual interfaces on a single
physical interface
■ Controller: Supports commands that configure controllers (for example, E1 and T1
controllers)
■ Line: Supports commands that configure the operation of a terminal line (for example, the
console or the vty ports)
■ Router: Supports commands that configure an IP routing protocol
If you enter the exit command, the router backs out one level, eventually logging out. In general,
you enter the exit command from one of the specific configuration modes to return to global
configuration mode. Press Ctrl-Z or enter end to leave configuration mode completely and return
to the privileged EXEC mode.
Commands that affect the entire device are called global commands. The hostname and enable
password commands are examples of global commands.
User EXEC Mode
Privileged EXEC Mode
Global Configuration Mode
RouterX>enable
RouterX#configure terminal
RouterX(config) #
Ctrl–z (end)
Exit
Configuration
Mode
Interface
Subinterface
Controller
Line
Router
RouterX(config–if)#
RouterX(config–subif)#
RouterX(config–controller)#
RouterX(config–line)#
RouterX(config–router)#
Prompt
6 Chapter 1: Review of Cisco IOS for Routers and Switches
Commands that point to or indicate a process or interface that will be configured are called major
commands. When entered, major commands cause the CLI to enter a specific configuration mode.
Major commands have no effect unless you immediately enter a subcommand that supplies the
configuration entry. For example, the major command interface serial 0 has no effect unless you
follow it with a subcommand that tells what is to be done to that interface.
Table 1-1 provides examples of some major commands and subcommands that go with them.
Notice that entering a major command switches from one configuration mode to another.
Help Facilities of the Cisco IOS CLI
Cisco IOS Software uses several command-line input help facilities, including context-sensitive
help. The following list provides details about the different help facilities of the Cisco IOS CLI.
■ Context-sensitive help: Provides a list of commands and the arguments associated with a
specific command.
■ Console error messages: Identifies problems with any Cisco IOS commands that are
incorrectly entered so that you can alter or correct them.
■ Command history buffer: Allows recall of long or complex commands or entries for reentry,
review, or corrections.
Context-sensitive help eliminates the need for memorization of Cisco IOS commands. At any time
during an EXEC session, you can enter a question mark (?) to get help. The following two types
of context-sensitive help are available:
■ Word help: Enter the ? command to get word help for a list of commands that begin with a
particular character sequence. Enter the character sequence followed immediately by the
question mark. Do not include a space before the question mark. The router displays a list of
commands that begin with the characters you entered.
Table 1-1 Major Commands and Subcommands
Major Command Subcommand
RouterX(config)#interface serial 0 RouterX(config-if)#shutdown
RouterX(config-if)#line console 0 RouterX(config-line)#password cisco
RouterX(config-line)#router rip RouterX(config-router)#network 10.0.0.0
NOTE You do not need to return to global configuration mode before entering another
configuration mode.
Cisco IOS CLI Functions 7
■ Command syntax help: Enter the ? command to get command syntax help for completing a
command. Enter a question mark in place of a keyword or argument. Include a space before
the question mark. The network device then displays a list of available command options.
Commands Review
This section reviews basic router and switch CLI commands in Cisco IOS Software. Table 1-2
outlines the Cisco IOS CLI commands used on both Cisco routers and switches to create a basic
configuration in a small network environment.
Table 1-2 Cisco IOS CLI Command Review
Command Description
banner motd Configures the Message-of-the-Day banner.
configure terminal From privileged EXEC mode, enters global configuration mode.
copy running-config startupconfig
Saves the running configuration into NVRAM as the startup
configuration.
enable Enters the privileged EXEC mode command interpreter.
enable secret password Sets an enable secret password to enter privilege EXEC.
erase startup-configuration Erases the startup configuration from memory.
hostname name Assigns the device a hostname.
interface interface Specifies an interface and enters interface configuration mode.
ip address address mask Sets the IP address and mask of the device.
ip default-gateway address Sets the default gateway of the switch.
line console 0 Specifies the console line and enters line configuration mode.
line vty 0 4 Specifies the vty lines and enters line configuration mode.
login Sets password checking at login.
password password Sets a password on a line.
ping ip address Uses Internet Control Message Protocol (ICMP) echo requests and
ICMP echo replies to determine whether a remote host is active.
reload Reboots the device.
show cdp neighbors Displays the Cisco Discovery Protocol updates received on each local
interface of the device.
show interfaces Displays information on all the device interfaces.
show running-configuration Displays the active configuration.
show startup-configuration Displays the configuration settings of the router NVRAM.
shutdown/no shutdown Disables or enables an interface.
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