Cisco IOS (originally Internetwork Operating System) is software used on most Cisco routers and switches. IOS is a package of routing, switching, security, and other internetworking technologies integrated into a single multitasking operating system.

The Cisco IOS portfolio supports a broad range of technologies and features. Customers choose an IOS based on a set of protocols and features supported by a particular image. Understanding the Cisco portfolio of feature sets is helpful in selecting the proper IOS to meet the needs of an organization.

Cisco made significant changes in the packaging and licensing of its IOS when transitioning from IOS 12.4 to 15.0. This chapter explains the naming conventions and packaging of IOS 12.4 and 15. Beginning with IOS 15, Cisco also implemented a new packaging format and licensing process for IOS. This chapter discusses the process of obtaining, installing, and managing Cisco IOS 15 software licenses.

Note: The release of IOS after 12.4 is 15.0. There is no IOS software release 13 or 14.