The Cisco IOS Software
Cisco routers run the Cisco Internetworking Operating System (IOS) with a command-line interface (CLI). The IOS also runs on some Cisco switch models, and it uses CLI. However, in some cases, the IOS CLI on a switch is slightly different than on a router. Furthermore, the IOS on the 1900 series switches is slightly different than on some other Cisco IOS-based switches.