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Router introduction

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Router

With a network that has hundreds or even thousands of computers

linked together, there has to be some agreed-upon way for those

devices to address one another and communicate.

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Router

As a network grows larger, it is not feasible for each

computer to keep track of the individual address of every

other computer on the network.

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Router

There must be some scheme for reducing the amount of information,

each computer has to hold locally in order to communicate with every

other computer.

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Router

The scheme used to involve splitting an large network into many

separate but connected networks

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Router

The job of keeping track of these discrete networks is

then given to specialized computers called routers.

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Routers Function

Routers are used to route packets from one network

number to another.

There are two things to consider with router:

You cannot configure the same network number on morethan one interface on a router.

A router does not forward broadcasts by default.

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Routers Components

There area two kinds of routers components:

Internal componentsoCPU (Central Processing Unit)

oROM (Read Only Memory)

oFLASH

oNVRAM (Nonvolatile RAM)

oRAM (Random Access Memory)

External component (interface)oWAN

oLAN

oConsole/AUX

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Routers Components

RAMROM FLASH NVRAM

Console

AuxiliaryInterface

CPU

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Internal Components:ROM

- Contains power-on diagnostics, a bootstrap program, and operating

system software.

- The main tasks for ROM are hardware diagnostics during router

bootup and loading the Cisco IOS software from flash to RAM.- ROMs are not erasable.

- They can only be upgraded by replacing the ROM chips in the

sockets.

RAMROM FLASH NVRAM

Consol

eAuxiliar

Interface

CPU

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Internal Components:RAM

- Random Access Memory (RAM) is split by the IOS into Main andShared memory.

- Main memory is used to store router configuration and IOS data

structures such as running-config, routing tables, switching cache, and

ARP tables...

- Shared memory buffers packets waiting to be processed (This type ofmemory is only used by 2500, 2600, 4000 routers. The 7000 routers have

a switch processor that controls the flow of packets through the router).

- The contents of RAM are lost when power is removed.

- RAM can be upgraded.

Main SharedROM FLASH NVRAM

Console

AuxiliaryInterface

CPU

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Internal Components:Flash

- Flash memory holds the full current version of IOS running on the

router.

- Flash memory is erasable memory that can be overwritten with

newer versions of the IOS.- The IOS may be in uncompressed or compressed form.

- In most routers (2600, 3600, 4000,) an executable copy of the

IOS is transferred to RAM during the boot process.

In other routers such as 2500, the IOS may be run directly fromflash.

RAMROM FLASH NVRAM

ConsoleAuxiliary

Interface

CPU

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Internal Components:NVRAM

- Nonvolatile random-access memory (NVRAM) is used to store the

startup configuration.

- (NVRAM) does not lose its contents when the router is turn off.

RAMROM FLASH NVRAM

Console

AuxiliaryInterface

CPU

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Internal Components:Buses

Most routers contain a System bus and a CPU bus.

The System bus is used for communication between the CPU andthe interfaces and/or expansion slots (This bus transfers the

packets to and from the interfaces).The CPU bus is used by the CPU for accessing components from

router storage (This bus transfers instructions and data to or from

specified memory addresses).

CPU

Interface

Memory

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External Components:Interface

The interfaces are the router connections to the outside.

The three types of interfaces are:

Local Area Network (LANs).

Wide Area Network (WANs).Management Ports (Console/AUX).

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