Information Technology Reference
In-Depth Information
Describe the Internal Components of a Router Exercise
Knowing the functions of the main internal components of a router is more important than knowing
the locations of the physical components inside a particular model. Therefore, in your own words,
provide a sufficiently detailed description of each component.
Component
Description
CPU
The central processing unit (CPU) executes the instructions of the operating
system. Among these functions are system initialization, routing functions, and
network interface control.
RAM
RAM is used for storing the IOS and for the working memory needed by the IOS.
This includes the routing table, running configurations, and packet queues, which
hold packets until the interface can be used to forward the packet. The contents of
RAM are lost when the router loses power.
Flash
Flash memory is used for storage of a full Cisco IOS Software image. In most
routers, a copy of the IOS is transferred to RAM from flash during the bootup
process. Physically, flash memory consists of single in-line memory modules
(SIMM) or PCMCIA cards, which can be upgraded to increase the amount of
flash. Flash memory does not lose its contents when the router loses power.
NVRAM
NVRAM is used to store the startup configuration. As described in Chapter 2,
“Static Routing,” a router will copy the startup configuration from NVRAM into
RAM when the router is initialized, and use the running configuration in RAM for
normal router operation. NVRAM retains its contents when the router loses
power.
Buses
Buses provide a physical means for the router to move bits between the different
components of the router. Most routers contain a system bus and a CPU bus. The
system bus is used to communicate 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 storage devices, like NVRAM and flash
memory.
ROM
ROM holds the bootstrap program, the ROM Monitor software, and optionally a
scaled-down version of the IOS. (Chapter 2 covers these types of software.)
ROMs are not erasable and can only be upgraded by replacing the ROM chips,
but ROM does retain its contents when the router loses power.
Power supply
The power supply converts the voltage and current of a standard power source to
the voltage and current required by the devices in the router. The power supplies
can be internal or external to the router chassis (the chassis is the metal box that
holds the components of the router), and some routers have multiple power
supplies for redundancy.
