Introduction to Cisco IOS

Internetwork Operating System (IOS) is the operating system that runs on all Cisco routers and switches. The primary function of the IOS is to manage the hardware resources and ensure that adequate memory and CPU cycles are available for the various processes that would run on the router.

The modern IOS has evolved from the original IOS that used to run on Cisco devices in the early days, and was rewritten to simplify and bring in modularity to the software. However, the basic functions remain unchanged.

The IOS runs a lot of processes on top of the fundamental operating system that manages the hardware and software resources on the router. These processes are the modules that implement the actual routing protocols, and perform tasks such as system configuration, maintenance, and troubleshooting.

The Cisco IOS command-line interface (CLI) is the primary user interface used for configuring, monitoring, and maintaining Cisco devices. The CLI can be accessed using a router console or terminal, or remotely by a telnet or ssh session into the router. All Cisco IOS commands are run through the CLI.