Cisco Router IOS (Internetwork Operating System) is the Cisco router proprietary operating system. IOS includes all the program, commands, and configuration options that the router uses to run and complete the tasks.
In Cisco router IOS system, the command interpreter mode is called router EXEC which is a terminal emulator software to interact with the router. in EXEC mode, the commands issued is used to view and modify the router configuration such as working in the router command modes, interacting with the router EXEC, and review the router configuration. See also the Cisco router access-list – a very important command in Cisco IOS to create security policy.
Router Command Modes
With Cisco Router IOS, you can configure the router using several different modes that allow you access the router in different levels of activity. Each of different command modes has different command tasks; therefore you need to be in the correct mode to complete specific tasks. For example, if you need to configure the IP address of a specific serial interface – you need to be in the correct serial interface mode such as int s0 or int s1.
The following is the summary of the Cisco router IOS command modes:
| Mode | Prompt | To enter | To exit |
| User EXEC | Router> | Start program | exit, logout, or disconnect |
| Privileged EXEC | Router# | enable | disable (exit disconnects) |
| Global configuration | Router(config)# | Config terminal or conf t | exit, ^z (to jump to the privileged exec |
| Line | Router(config-line)# | line | exit |
| Interface | Router(config-if)# | Interface | Exit |
| Subinterface | Router(config-subif)# | Interface | Exit |
| Router | Router(config-router)# | Router | Exit |
| Setup | - | Setup or
erase startup-config |
^C |
Cisco router IOS is an advanced command-line program, and includes help and features to help you simplify working with the router. When you type the commands on the command line, the IOS receives them, interprets them, and then executes them.
Advanced editing summary
There are several similarities between the Cisco router IOS and the UNIX editing. The following lists summarize the router advanced editing features.
| Use the keystroke below to | To move |
| <Ctrl> +A | To the beginning of the line |
| <Ctrl> +E | To the end of the line |
| <Ctrl> +B | Back one character |
| <Ctrl> +F | Forward one character |
| Right arrow | Forward one character |
| Left arrow | Back one character |
| <Esc> +B | Back one ward |
| <Esc> +F | Forward one word |
You can use the terminal editing command to turn on the advanced editing, and the command terminal no editing to turn it off.
When you are in the command editing mode, the $ indicator appears after the prompt, and as you type the commands longer than the command line appear to scroll under the prompt.
Help Commands
Cisco router IOS provides ‘Help’ in all router modes which are context sensitive – the information depends on what you are doing and which mode you are in. by typing the partial words with the ? and pressing Enter, you will be prompted with a list of matching commands.
| If you want to … | You can use … |
| Show list of all commands available in the current mode | ? |
| Show commands that begin with specific letter(s) | xx? – no spaces |
| Show keywords for a command | Command ? – need space between command and ? |
| Get the full command from a partial command | Partial command + <tab> – no spaces |
With Cisco router IOS, you can use the shortened version commands, for example you can shorten the ‘configuration terminal’ to ‘conf t’ and so on.
Show command is available both in User and privileged EXEC modes; it is very helpful to review the status and any information of the routers such as in the following:
| You can use this command | To do the following |
| show version | Review the hardware configuration, IOS version, and RAM information |
| Show running-config | Review the running configuration file |
| Show startup-config | Review the startup configuration which is stored in NVRAM |
| Show flash | Review the size of the configuration files and the available flash memory |
| Show history | View the commands in the command history list |
You can shorten the show command for example you can use ‘sh run’ for the ‘show running-config’ command.
See also:
- Common router problems
- Surfboard cable modem with router
- Guideline in router connection
- Speedup internet connection guidelines
- Router setting guide
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