some key points that summarize the IOS Basic

Posted: 19 Feb 2017 in CCNA
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In this tutorial we will learn CISCO IOS basics. we will learn about the types of memory used in cisco devices like cisco routers and cisco switches.We will also focus on Cisco IOS Boot Process. We wil Learn how IOS is loaded in memory of cisco devices and different modes of Routers and switches.

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Types of Memory on CISCO Devices:

There are different types of memory on a Cisco Devices

·         ROM  : The Read-only memory (ROM) on a Cisco device is like the rom on computer in the sense that it stores POST and boot loader program. The boot loader program is responsible for locating the IOS.
·         FLASH   Memory: The flash memory is use to store the Cisco IOS.
·         RAM : RAM is used to store things like the routing table on a router, or MAC address table on switch. It is also used to store the Running-config.
 Please Note that RAM is also known as Volatile RAM.
·         NVRAM :  Non-Volatile RAM is used to store the startup-config, which is copied to the running-config on bootup after the IOS is loaded.

    IOS The Boot Process:

Now it’s time to understand the Booting process of Cisco devices.
·         The first thing that happens when a cisco device boots up is the POST routing , which is responsible for performing a self-diagnostic to verify everything is functioning on the router or switch.

·         LOCATE IOS :

After the post , The configuration register is checked to find from where the ios have to be loaded . If IOS In FLASH MEMORY is will be locate into RAM. If IOS is not present in the flash memory then it will check TFTP server or ROM.


After the IOS is loaded into Memory, the boot loader program then locates the startup-config and applies it to the devices. If there is no start-up config , the router goes to initial mode.

Configuration Modes of Cisco Devices:

whenever we need to make some changes to the Cisco device like cisco router or cisco switches, there are a number of different configuration modes, and each change is made in specific configuration mode.

Major configuration modes in CISCO DEVICES.

·         User Exec:

When you connect to a Cisco device, the default configuration mode is uer exec mode. With user exec mode, you can view the settings on device but you cannot  make any changes in cisco router or cisco switches in this mode.
Now to Identify this mode see it’s prompt.
 The IOS prompt display a “>”

·         Privilege Mode :

If you wanted to make some  change to the cisco devices like cisco routers and cisco switches, you must navigate to privilege mode .
Privilege mode displays with a “#” in the prompt.
You can control access to privilege mode using password like enable password or enable secret password.

·         Global Configuration Mode :

Global configuration mode is where you go to make global changes to the router such as the hostname, routing and many more.
To navigate to global configuration mode from privilege mode, you have type config  terminal ,where you will be placed at the “(config)#” prompt



·         Sub Prompts or sub Interface mode:

 You can navigate to a number of different sub prompts from global configuration ,such as interface prompts to modify setting on specific interface and line prompts to modify the different ports on the device .
I hope this article will help you understand Cisco IOS and its functioning well.If you have any doubt or suggestion kindly put your views through comment.

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