Cisco IOS enables network services in switches and routers. It provides the following features:
The Cisco IOS command-line interface (CLI) can be accessed through a console connection, modem connection, or Telnet/SSH sessions. These connections are called EXEC sessions.
When a Cisco device starts up, it goes through the following steps:
Step 1. Completes power-on self test (POST)
Step 2. Finds and loads Cisco IOS Software image
Step 3. Finds and applies device configuration
An IOS device can be configured from any of the following external sources: