CCNA 4.1 Cisco Internetwork Operating System (IOS) User Interface

• IOS is the kernel of Cisco routers & switches. (part of OS which allocates resources and manages low-level hardware interfaces and security)
• Cisco router IOS is responsible for network protocol functionality, traffic between devices, network security, network scalability and reliability.
• Access to the IOS command line is called an EXEC session
• Cisco router IOS can be accessed through console port, auxiliary port & telnet (in band)
• After Cisco router is turned on, it will run a Power On Self Test (POST). If pass, it will load the Cisco IOS from flash memory (EEPROM) and start-up config from RAM/NVRAM
• On non-ISR router, when there is no config file on NVRAM, the router will broadcast through TFTP host for a valid config file. If no file is found, the router will enter setup mode