Understanding Components of a Cisco Router

Posted: October 12, 2012 in Networking
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So, What is a router??

Well, a router is a specialized computer used for networking. The main function of a router is route packets.  A router is just like a typical PC, has a CPU and memory components. In Cisco routers, it has the Cisco IOS which provides the basic routing logic. The router also has a ROM just like normal PCs, which contains the basic software to be run when the router is booted.

Example of a router

Internal Components of a Cisco Router:

A router consists of the following major components:

  1. CPU
  2. ROM
  3. RAM
  4. NVRAM
  5. Flash Memory
  6. RXBOOT  Image
  7. Interfaces
  8. Buses
  9. Power Supply
  10. Configuration Register

CPU: The CPU executes the instructions of the operating system. They also perform functions such as system initialization, routing functions, and network interface control.

ROM: This maintains the instructions for POST (Power on Self Test) for diagnosis and also stores the bootstrap program and basic OS software.

RAM: It stores the routing tables and the configuration file while the router is powered on. The “running-config” is stored here. The contents of the RAM are lost when the router is restarted or powered down.

NVRAM: It stores the “startup-config” file. The contents in the NVRAM remain even after the router is shutdown or rebooted.

Flash Memory: This is the location where the “Cisco IOS image file” is stored which is the operating system of the router itself. The contents in the flash memory remain even after reboot or shutdown. This is a type of EEPROM.

RXBOOT Image: This is a cut-down version of the the IOS located in the router’s ROM.

Buses: Most routers consist of a system bus and a CPU bus. Buses provide physical means for the router to move bits among the different components of the router. Most routers contain a system bus and a CPU bus.  The system bus communicates between the CPU and the interfaces. For example, this bus transfers the packets to and from the interfaces. The CPU bus is used by the CPU for accessing router’s storage devices like NVRAM and flash memory.

Interfaces: They are physical connectors that connect the router to the network for packet entry and exit.

Power Supply: The power supplies can be internal or external to the router. Some routers have multiple power supplies for redundancy.

Configuration Register: The configuration register is what decides if the router is going to boot from the IOS image from the tftp server or the RXBOOT image.



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