Table Of Contents

Using Cisco IOS Software

Understanding Command Modes

Getting Help

Example: How to Find Command Options

Using the no and default Forms of Commands

Saving Configuration Changes

Filtering Output from the show and more Commands

Finding Support Information for Platforms and Cisco IOS Software Images

Using Cisco Feature Navigator

Using Software Release Notes

Using Cisco IOS Software

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This chapter provides helpful tips for understanding and configuring Cisco IOS software using the command-line interface (CLI). It contains the following sections:

•Understanding Command Modes

•Getting Help

•Using the no and default Forms of Commands

•Saving Configuration Changes

•Filtering Output from the show and more Commands

•Finding Support Information for Platforms and Cisco IOS Software Images

For an overview of Cisco IOS software configuration, refer to the Cisco IOS Configuration Fundamentals and Network Management Configuration Guide.

For information on the conventions used in the Cisco IOS software documentation set, refer to"About Cisco IOS Software Documentation."

Understanding Command Modes

You use the CLI to access Cisco IOS software. Because the CLI is divided into many different modes, the commands available to you at any given time depend on the mode that you are currently in. Entering a question mark (?) at the CLI prompt allows you to obtain a list of commands available for each command mode.

When you log in to the CLI, you are in user EXEC mode. User EXEC mode contains only a limited subset of commands. To have access to all commands, you must enter privileged EXEC mode, normally by using a password. From privileged EXEC mode you can issue any EXEC command—user or privileged mode—or you can enter global configuration mode. Most EXEC commands are one-time commands. For example, show commands show important status information, and clear commands clear counters or interfaces. The EXEC commands are not saved when the software reboots.

Configuration modes allow you to make changes to the running configuration. If you later save the running configuration to the startup configuration, these changed commands are stored when the software is rebooted. To enter specific configuration modes, you must start at global configuration mode. From global configuration mode, you can enter interface configuration mode and a variety of other modes, such as protocol-specific modes.

ROM monitor mode is a separate mode used when the Cisco IOS software cannot load properly. If a valid software image is not found when the software boots or if the configuration file is corrupted at startup, the software might enter ROM monitor mode.

Table 1 describes how to access and exit various common command modes of the Cisco IOS software. It also shows examples of the prompts displayed for each mode.

Table 1 Accessing and Exiting Command Modes

Command Mode	Access Method	Prompt	Exit Method
User EXEC	Log in.	Router>	Use the logout command.
Privileged EXEC	From user EXEC mode, use the enable EXEC command.	Router#	To return to user EXEC mode, use the disable command.
Global configuration	From privileged EXEC mode, use the configure terminal privileged EXEC command.	Router(config)#	To return to privileged EXEC mode from global configuration mode, use the exit or end command.
Interface configuration	From global configuration mode, specify an interface using an interface command.	Router(config-if)#	To return to global configuration mode, use the exit command. To return to privileged EXEC mode, use the end command.
ROM monitor	From privileged EXEC mode, use the reload EXEC command. Press the Break key during the first 60 seconds while the system is booting.	>	To exit ROM monitor mode, use the continue command.

For more information on command modes, refer to the "Using the Command-Line Interface" chapter in the Cisco IOS Configuration Fundamentals and Network Management Configuration Guide.

Getting Help

Entering a question mark (?) at the CLI prompt displays a list of commands available for each command mode. You can also get a list of keywords and arguments associated with any command by using the context-sensitive help feature.

To get help specific to a command mode, a command, a keyword, or an argument, use one of the following commands:

Command	Purpose
help	Provides a brief description of the help system in any command mode.
abbreviated-command-entry?	Provides a list of commands that begin with a particular character string. (No space between command and question mark.)
abbreviated-command-entry<Tab>	Completes a partial command name.
?	Lists all commands available for a particular command mode.
command ?	Lists the keywords or arguments that you must enter next on the command line. (Space between command and question mark.)

Example: How to Find Command Options

This section provides an example of how to display syntax for a command. The syntax can consist of optional or required keywords and arguments. To display keywords and arguments for a command, enter a question mark (?) at the configuration prompt or after entering part of a command followed by a space. The Cisco IOS software displays a list and brief description of available keywords and arguments. For example, if you were in global configuration mode and wanted to see all the keywords or arguments for the arap command, you would type arap ?.

The <cr> symbol in command help output stands for "carriage return." On older keyboards, the carriage return key is the Return key. On most modern keyboards, the carriage return key is the Enter key. The <cr> symbol at the end of command help output indicates that you have the option to press Enter to complete the command and that the arguments and keywords in the list preceding the <cr> symbol are optional. The <cr> symbol by itself indicates that no more arguments or keywords are available and that you must press Enter to complete the command.

Table 2 shows examples of how you can use the question mark (?) to assist you in entering commands. The table steps you through configuring an IP address on a serial interface on a Cisco 7206 router that is running Cisco IOS Release 12.0(3).

Table 2 How to Find Command Options 

Command	Comment
Router> enable Password: <password> Router#	Enter the enable command and password to access privileged EXEC commands. You are in privileged EXEC mode when the prompt changes to Router#.
Router# configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#	Enter the configure terminal privileged EXEC command to enter global configuration mode. You are in global configuration mode when the prompt changes to Router(config)#.
Router(config)# interface serial ?   <0-6>     Serial interface number Router(config)# interface serial 4 ?   / Router(config)# interface serial 4/ ?   <0-3>     Serial interface number Router(config)# interface serial 4/0 ? <cr> Router(config)# interface serial 4/0 Router(config-if)#	Enter interface configuration mode by specifying the serial interface that you want to configure using the interface serial global configuration command. Enter ? to display what you must enter next on the command line. In this example, you must enter the serial interface slot number and port number, separated by a forward slash. When the <cr> symbol is displayed, you can press Enter to complete the command. You are in interface configuration mode when the prompt changes to Router(config-if)#.
Router(config-if)# ? Interface configuration commands:   .   .   .   ip                  Interface Internet Protocol config commands   keepalive           Enable keepalive   lan-name            LAN Name command   llc2                LLC2 Interface Subcommands   load-interval       Specify interval for load calculation for an                       interface   locaddr-priority    Assign a priority group   logging             Configure logging for interface   loopback            Configure internal loopback on an interface   mac-address         Manually set interface MAC address   mls                 mls router sub/interface commands   mpoa                MPOA interface configuration commands   mtu                 Set the interface Maximum Transmission Unit (MTU)   netbios             Use a defined NETBIOS access list or enable                       name-caching   no                  Negate a command or set its defaults   nrzi-encoding       Enable use of NRZI encoding   ntp                 Configure NTP   .   .   . Router(config-if)#	Enter ? to display a list of all the interface configuration commands available for the serial interface. This example shows only some of the available interface configuration commands.
Router(config-if)# ip ? Interface IP configuration subcommands:   access-group        Specify access control for packets   accounting          Enable IP accounting on this interface   address             Set the IP address of an interface   authentication      authentication subcommands   bandwidth-percent   Set EIGRP bandwidth limit   broadcast-address   Set the broadcast address of an interface   cgmp                Enable/disable CGMP   directed-broadcast  Enable forwarding of directed broadcasts   dvmrp               DVMRP interface commands   hello-interval      Configures IP-EIGRP hello interval   helper-address      Specify a destination address for UDP broadcasts   hold-time           Configures IP-EIGRP hold time   .   .   . Router(config-if)# ip	Enter the command that you want to configure for the interface. This example uses the ip command. Enter ? to display what you must enter next on the command line. This example shows only some of the available interface IP configuration commands.
Router(config-if)# ip address ?   A.B.C.D             IP address   negotiated          IP Address negotiated over PPP Router(config-if)# ip address	Enter the command that you want to configure for the interface. This example uses the ip address command. Enter ? to display what you must enter next on the command line. In this example, you must enter an IP address or the negotiated keyword. A carriage return (<cr>) is not displayed; therefore, you must enter additional keywords or arguments to complete the command.
Router(config-if)# ip address 172.16.0.1 ?   A.B.C.D             IP subnet mask Router(config-if)# ip address 172.16.0.1	Enter the keyword or argument that you want to use. This example uses the 172.16.0.1 IP address. Enter ? to display what you must enter next on the command line. In this example, you must enter an IP subnet mask. A <cr> is not displayed; therefore, you must enter additional keywords or arguments to complete the command.
Router(config-if)# ip address 172.16.0.1 255.255.255.0 ?   secondary           Make this IP address a secondary address   <cr> Router(config-if)# ip address 172.16.0.1 255.255.255.0	Enter the IP subnet mask. This example uses the 255.255.255.0 IP subnet mask. Enter ? to display what you must enter next on the command line. In this example, you can enter the secondary keyword, or you can press Enter. A <cr> is displayed; you can press Enter to complete the command, or you can enter another keyword.
Router(config-if)# ip address 172.16.0.1 255.255.255.0 Router(config-if)#	In this example, Enter is pressed to complete the command.

Using the no and default Forms of Commands

Almost every configuration command has a no form. In general, use the no form to disable a function. Use the command without the no keyword to reenable a disabled function or to enable a function that is disabled by default. For example, IP routing is enabled by default. To disable IP routing, use the no ip routing command; to reenable IP routing, use the ip routing command. The Cisco IOS software command reference publications provide the complete syntax for the configuration commands and describe what the no form of a command does.

Configuration commands can also have a default form, which returns the command settings to the default values. Most commands are disabled by default, so in such cases using the default form has the same result as using the no form of the command. However, some commands are enabled by default and have variables set to certain default values. In these cases, the default form of the command enables the command and sets the variables to their default values. The Cisco IOS software command reference publications describe the effect of the default form of a command if the command functions differently than the no form.

Saving Configuration Changes

Use the copy system:running-config nvram:startup-config command to save your configuration changes to the startup configuration so that the changes will not be lost if the software reloads or a power outage occurs. For example:

Router# copy system:running-config nvram:startup-config

Building configuration...

It might take a minute or two to save the configuration. After the configuration has been saved, the following output appears:

[OK]

Router#

On most platforms, this task saves the configuration to NVRAM. On the Class A Flash file system platforms, this task saves the configuration to the location specified by the CONFIG_FILE environment variable. The CONFIG_FILE variable defaults to NVRAM.

Filtering Output from the show and more Commands

You can search and filter the output of show and more commands. This functionality is useful if you need to sort through large amounts of output or if you want to exclude output that you need not see.

To use this functionality, enter a show or more command followed by the "pipe" character (|); one of the keywords begin, include, or exclude; and a regular expression on which you want to search or filter (the expression is case-sensitive):

command | {begin | include | exclude} regular-expression

The output matches certain lines of information in the configuration file. The following example illustrates how to use output modifiers with the show interface command when you want the output to include only lines in which the expression "protocol" appears:

Router# show interface | include protocol

FastEthernet0/0 is up, line protocol is up

Serial4/0 is up, line protocol is up

Serial4/1 is up, line protocol is up

Serial4/2 is administratively down, line protocol is down

Serial4/3 is administratively down, line protocol is down

For more information on the search and filter functionality, refer to the "Using the Command-Line Interface" chapter in the Cisco IOS Configuration Fundamentals and Network Management Configuration Guide.

Finding Support Information for Platforms and Cisco IOS Software Images

Cisco IOS software is packaged in feature sets consisting of software images that support specific platforms. The feature sets available for a specific platform depend on which Cisco IOS software images are included in a release. To identify the set of software images available in a specific release or to find out if a feature is available in a given Cisco IOS software image, you can use Cisco Feature Navigator or the software release notes.

Using Cisco Feature Navigator

Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.

Using Software Release Notes

Cisco IOS software releases include release notes that provide the following information:

•Platform support information

•Memory recommendations

•New feature information

•Open and resolved severity 1 and 2 caveats for all platforms

Release notes are intended to be release-specific for the most current release, and the information provided in these documents may not be cumulative in providing information about features that first appeared in previous releases. Refer to Cisco Feature Navigator for cumulative feature information.