The Cisco IOS Command Line Summary (27.4)
The following is a summary of each topic in the module:
What Did I Learn in this Module? (27.4.1)
• IOS Navigation—The Cisco IOS CLI is a text-based program that enables entering and executing Cisco IOS commands to configure, monitor, and maintain Cisco devices. The Cisco CLI can be used with either in-band or out-of-band management tasks.
CLI commands are used to alter the configuration of the device and to display the current status of processes on the router. When the router has completed the power-up sequence and the Router> prompt appears, the CLI can be used to enter Cisco IOS commands.
As a security feature, the Cisco IOS software separates management access into the following two command modes:
- User EXEC Mode — This mode is useful for basic operations. It allows a limited number of basic monitoring commands but does not allow the execution of any commands that might change the configuration of the device. The user EXEC mode is identified by the CLI prompt that ends with the > symbol.
- Privileged EXEC Mode — To execute configuration commands, a network administrator must access privileged EXEC mode. The privileged EXEC mode can be identified by the prompt ending with the # symbol. Higher configuration modes, like global configuration mode, can only be reached from privileged EXEC mode. Global configuration mode is identified by the CLI prompt that ends with (config)#.
The commands used to navigate between the different IOS command modes are:
- enable
- disable
- configure terminal
- exit
- end
- Ctrl+Z
- line console 0
- line vty 0 15
- interface vlan 1
- The Command Structure—Each IOS command has a specific format or syntax and can only be executed in the appropriate mode.
The general syntax for a command is the command followed by any appropriate keywords and one or more arguments: - Boldface text indicates commands and keywords.
- Italicized text indicates an argument for which the user provides the value.
- Square brackets [x] indicate an optional element.
- Braces {x} indicate a required element.
- Braces and vertical lines within square brackets [x {y | z}] indicate a required choice within an optional element.
The IOS CLI provides hot keys (e.g., tab, backspace, Ctrl-C, etc.) and shortcuts (e.g., conf for configure). These make configuring, monitoring, and troubleshooting easier. - View Device Information—A typical show command can provide information about the configuration, operation, and status of parts of a Cisco switch or router. Some of the more popular show commands are:
- show running-config
- show interfaces
- show arp
- how ip route
- show protocols
- show version
Have you ever watched a movie or television program where some smart person was typing away at a computer to circumvent a security measure and gain unauthorized access to files? They weren’t typing a novel; they were using the command line interface. While you can employ a user interface to configure most network devices, becoming familiar with and using commands is so much faster. If you must troubleshoot your network, you’ll need to use commands. Yes, it’s a bit like learning a new language, but you know right away if you did it correctly or not. Once you start to use commands, you may never go back to the user interface. What would you like to be able to do with commands?