Cisco RouterCisco Router

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Internetworking Devices

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Broadcast and Collision Domain

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Broadcast and Collision Domain

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Broadcast and Collision Domain

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Broadcast and Collision Domain

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Using Cisco IOS Command Line Interface (CLI)

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Cisco IOSCisco IOS

Cisco technology is built around the CiscoInternetwork Operating System (IOS), which is thesoftware that controls the routing and switchingfunctions of internetworking devices.

A solid understanding of the IOS is essential fora network administrator.

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Introduction to Routers

A router is a special type of computer. It has the same basic components as a standard desktopC d i d f ifi f iPC. However, routers are designed to perform some very specific functions. Just as computers

need operating systems to run software applications, routers need the Internetwork OperatingSystem software (IOS) to run configuration files. These configuration files contain theinstructions and parameters that control the flow of traffic in and out of the routers. The manyinstructions and parameters that control the flow of traffic in and out of the routers. The manyparts of a router are shown below:

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Router Memory ComponentsRouter Memory Components

ROM - Read Only Memory – Bootstrap/POST

FLASH MFLASH Memory - IOS Images are kept here- Erasable reprogrammable ROM- Contents are kept on Power down or reload

RAM - Random Access memory- Routing TablesRouting Tables- Running Configuration- Contents are lost on reboot

NVRAM - Start up configuration- Configuration Register

Contents are kept on reload

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- Contents are kept on reload

ROMROM

Read-Only Memory

ROM has the following characteristics and functions:

Maintains instructions for power-on self test (POST) diagnostics

Stores bootstrap program and basic operating system software

Mini IOS

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RAMRAM

Random Access Memory, also called dynamic RAM (DRAM)

RAM h th f ll i h t i ti d f tiRAM has the following characteristics and functions:

Stores routing tables Stores routing tables Holds ARP cache Performs packet buffering (shared RAM) Provides temporary memory for the configuration file of

the router while the router is powered on L t t h t i d d t t d Loses content when router is powered down or restarted

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NVRAMNVRAM

Non-Volatile RAM

NVRAM has the following characteristics and functions:

Provides storage for the startup configuration file Retains content when router is powered down or

restarted Configuration Register – 16 bit register whichdecides boot sequence

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FlashFlash

Fl h h th f ll i h t i ti dFlash memory has the following characteristics and functions:

Holds the operating system image (IOS) All ft t b d t d ith t Allows software to be updated without

removing and replacing chips on the processor Retains content hen o te is po e ed do n Retains content when router is powered down

or restarted Can store multiple versions of IOS software Can store multiple versions of IOS software Is a type of electronically erasable,

programmable ROM (EEPROM)

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programmable ROM (EEPROM)

InterfacesInterfacesInterfaces have the following characteristics and functions:

Connect router to network for frame entry and exit Can be on the motherboard or on a separate moduleCan be on the motherboard or on a separate module

Types of interfaces:

Ethernet Fast Ethernet Fast Ethernet Serial ISDN BRI Loopback Console Aux

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Aux

Router Internal Components

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Router Bootup Sequence

1. Perform power-on self test (POST).

2. Load and run bootstrap code.

3. Find the Cisco IOS software.

4. Load the Cisco IOS software.

5. Find the configuration.

6. Load the configuration.g

7. Run the configured Cisco IOS

software.

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Loading the Cisco IOS Software oad g t e C sco OS So t a eFrom Flash Memory

• The flash memory file is decompressed into RAM.

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y p

Loading the Configuration

• Load and execute the configuration from NVRAM.If fi ti i t i NVRAM t t d

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• If no configuration is present in NVRAM, enter setup mode.

IOS File System Overview

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Overview of Router & Switch Modes

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Viewing the Configuration

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show running-config and show startup-config Commands

Di l th t d d fi ti• Displays the current and saved configuration

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