wires plugged in device

What is Router?

Router– It is a network device that forwards data packets across networks. Routers perform “data traffic directing” service on the Internet. It is a microprocessor-controlled device that is connected to two or more data lines from different networks.

What inside a Router?

router inside
  • CPU– The CPU executes operating system instructions, such as process routing data.
  • RAM– RAM stores the instructions and data needed to be executed by the CPU. Router expand IOS in it upon boot. it hold- Packet buffers, ARP cache, routing tables, Running-config. It also known as DRAM.
  • ROM– Cisco devices use ROM to store: The bootstrap instructions, ROM monitor software, Basic diagnostic software, Scaled-down version of IOS. Used to start and maintain the router.
  • Flash memory- Stores the Cisco IOS by default. Flash memory is not erased when the router is reloaded. It is EEPROM created by Intel.
  • NVRAM (nonvolatile RAM)- Used to hold the routers startup-configuration. NVRAM is not erased when the router or switch is reloaded. The configuration register is stored in NVRAM.
  • Mini-IOS- Called the RXBOOT or bootloader by Cisco, the mini-IOS is a small IOS in ROM that can be used to bring up an interface and load a Cisco IOS into flash memory. The mini-IOS can also perform a few other maintenance operations.
  • POST- Stored in the microcode of the ROM, the POST is used to check the basic functionality of the router hardware and determine which interfaces are present.
  • Bootstrap- Stored in the microcode of the ROM, the bootstrap is used to bring a router up during initialization. It will boot the router and then load the IOS.
  • ROM monitor- Stored in the microcode of the ROM, the ROM monitor is used for manufacturing, testing, and troubleshooting.
  • Configuration register- Used to control how the router boots up. Default value is set to 0x2102 (#sh version). The default setting tells the router to load the IOS from flash memory as well as to load the configuration from NVRAM.

Booting Process of a router

A router typically goes through five steps when booting up-

  1. POST- First the router runs POST (located in ROM) to detect and initialize The routers hardware components, including memory and interfaces.
  2. Bootstrap loading- The bootstrap program is loaded and executed.
  3. Load IOS- The bootstrap program finds and loads an IOS image, present in Flash memory, TFTP server, or the Mini-IOS in ROM.
  4. Search NVRAM data- Once the IOS is loaded, it find and load a configuration file from NVRAM. If there is no configuration file, then it starts up the System Configuration Dialog.
  5. After the configuration is loaded, you are presented with the CLI interface.

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