CISCO IOS– CISCO IOS stands for International Operating System.

CISCO IOS is a type of Os which install Cisco routers and Switches. It is propriety solution of CISCO.

The First IOS developed in 1986 by ‘WILLIAM YAGARS‘ It is responsible for—

  1. Carry Network protocol and function.
  2. Provide security.
  3. Provide High-Speed Network Traffic.

These are different kinds of IOS version developed by CISCO. Its latest version is 150.

The router is a layer 3(Network Layer) device, which connects two or more different network. It also Provides the best route between source and destination.




  1. EXTERNAL COMPONENTS-    These are different kinds of an external component of the router.
  • SERIAL PORT– Router to WAN connectivity.
  • ETHERNET PORT–LAN connectivity.
  • BRI–Basic Rate Interface(ISDN Connectivity).
  • AUI–Additional LAN Port
  • AUX–Auxillary Port(WAN Connectivity).
  • CONSOLE PORT–To configure the Router/switch from Computer.


  • MOTHERBOARD– Gives a platform to connect all the devices.
  • ROM–(Read Only Memory) It has four components.
  • RAM– It is a volatile memory, which holds the only active configuration of the router. It also holds routing table and ARP table.
  • NV-RAM–It is a non-volatile memory, which stores startup configuration.
  •  FLASH MEMORY– It contents IOS of the router.

It is a 16-bit value which is represented in the hexadecimal format that tells the router from where it will boot.


There are four type of REGISTRY VALUE–

  • 0*2100–This value tells the router to boot from ROM MONITOR MODE(SAFE MODE).
  • 0*2101–This value tells the router to boot from mini IOS.
  • 0*2102–This value tells the router to boot from FLASH with NVRAM/startup configuration. It is the default configuration REGISTRY VALUE.
  • 0*2142–This value tells the router to boot from FLASH, but ignore NVRAM configuration (Used for Password breaking).


  1. POST
  3. FLASH
  4. NVRAM
  5. RAM




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