The Cisco IOS user interface is divided into many different modes. The commands available to you depend on which mode you are currently in. Enter a question mark (?) at the system prompt to obtain a list of commands available for each command mode.

You can start a CLI session through a console connection, through Telnet, a SSH, or by using the browser.

When you start a session, you begin in user mode, often called user EXEC mode. Only a limited subset of the commands are available in user EXEC mode. For example, most of the user EXEC commands are one-time commands, such as show commands, which show the current configuration status, and clear commands, which clear counters or interfaces. The user EXEC commands are not saved when the controller reboots.

To have access to all commands, you must enter privileged EXEC mode. Normally, you must enter a password to enter privileged EXEC mode. From this mode, you can enter any privileged EXEC command or enter global configuration mode.

Using the configuration modes (global, interface, and line), you can make changes to the running configuration. If you save the configuration, these commands are stored and used when the controller reboots. To access the various configuration modes, you must start at global configuration mode. From global configuration mode, you can enter interface configuration mode and line configuration mode.

This table describes the main command modes, how to access each one, the prompt you see in that mode, and how to exit the mode.

Controller>

Controller#

Controller(config)#

Controller(config-vlan)#

Controller(config-if)#

Controller(config-line)#

1.    help


2.    abbreviated-command-entry ?


3.    abbreviated-command-entry <Tab>


4.    ?


5.    command ?


6.    command keyword ?

Controller# help

Controller# di?
dir disable disconnect 

Controller# sh conf<tab>
Controller# show configuration

Controller> ?

Controller> show ?

Controller(config)# cdp holdtime ?
  <10-255> Length of time (in sec) that receiver must keep this packet 

You need to enter only enough characters for the controller to recognize the command as unique.

This example shows how to enter the show configuration privileged EXEC command in an abbreviated form:

Controller# show conf

Almost every configuration command also has a no form. In general, use the no form to disable a feature or function or reverse the action of a command. For example, the no shutdown interface configuration command reverses the shutdown of an interface. Use the command without the keyword no to reenable a disabled feature or to enable a feature that is disabled by default.

Configuration commands can also have a default form. The default form of a command returns the command setting to its default. Most commands are disabled by default, so the default form is the same as the no form. However, some commands are enabled by default and have variables set to certain default values. In these cases, the default command enables the command and sets variables to their default values.

This table lists some error messages that you might encounter while using the CLI to configure your controller.

% Ambiguous command: "show con"

% Incomplete command.

% Invalid input detected at ‘^’ marker.

You can log and view changes to the controller configuration. You can use the Configuration Change Logging and Notification feature to track changes on a per-session and per-user basis. The logger tracks each configuration command that is applied, the user who entered the command, the time that the command was entered, and the parser return code for the command. This feature includes a mechanism for asynchronous notification to registered applications whenever the configuration changes. You can choose to have the notifications sent to the syslog.

Note	Only CLI or HTTP changes are logged.

1.    terminal history [size number-of-lines]

Controller# terminal history size 200

To recall commands from the history buffer, perform one of the actions listed in this table. These actions are optional.

Note	The arrow keys function only on ANSI-compatible terminals such as VT100s.

1.    Ctrl-P or use the up arrow key


2.    Ctrl-N or use the down arrow key


3.    show history

Controller# show history

1.    terminal no history

Controller# terminal no history

You can use a wraparound feature for commands that extend beyond a single line on the screen. When the cursor reaches the right margin, the command line shifts ten spaces to the left. You cannot see the first ten characters of the line, but you can scroll back and check the syntax at the beginning of the command. The keystroke actions are optional.

To scroll back to the beginning of the command entry, press Ctrl-B or the left arrow key repeatedly. You can also press Ctrl-A to immediately move to the beginning of the line.

Note	The arrow keys function only on ANSI-compatible terminals such as VT100s.

The following example shows how to wrap a command line that extends beyond a single line on the screen.

1.    access-list


2.    Ctrl-A


3.    Return key

Controller(config)# access-list 101 permit tcp 10.15.22.25 255.255.255.0 10.15.22.35
Controller(config)# $ 101 permit tcp 10.15.22.25 255.255.255.0 10.15.22.35 255.25
Controller(config)# $t tcp 10.15.22.25 255.255.255.0 131.108.1.20 255.255.255.0 eq
Controller(config)# $15.22.25 255.255.255.0 10.15.22.35 255.255.255.0 eq 45 

Controller(config)# access-list 101 permit tcp 10.15.22.25 255.255.255.0 10.15.2$