IOS – Internetwork Operating System
Cisco ‘Internetwork Operating System’ is a multitasking, command based, configurable operating system that runs on Cisco routers and switches. It is a proprietary operating system developed by Cisco Systems of USA.
The IOS is usually stored in a flash memory and loaded on to the RAM during the boot process. The start-up configuration files are usually stored on a non-volatile RAM.
How to access the IOS on a Cisco device?
The simplest way to access the IOS is by connecting a PC to the console port of the device. Alternately, an operating system could be accessed remotely using an application layer protocol “Telnet”.
An IOS operating system usually comes with 3 access modes: a user EXEC mode, a privileged EXEC mode and a global configuration mode. A user EXEC mode is basically used to view the basic information. A Privileged mode is used for advanced management, and the global configuration mode is used to configure a networking device.
A Cisco IOS has a complete control over the networking device hardware, on which it is installed. It provides a ‘great’ interface to a user to configure router & switching functions including: routing protocols, access lists, switching functions and security features.