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Router Fundamentals

(Ref. CCNA5 Introduction to Networks 2.1, 6.3)

A Router is a Computer

Router CPU and OS

Cisco IOS – Collection of network operating systems used on Cisco devices

All networking devices come with a default IOS Switch or router IOS provides options to:

Configure interfaces Enable routing and switching functions

Possible to upgrade the IOS version or feature set

Operating System

Cisco IOS stored in Flash Non-volatile storage, not lost when power is lost Can be changed or overwritten as needed Can be used to store multiple versions of IOS IOS copied from flash to volatile RAM Quantity of flash and RAM memory determines IOS that can be used

Location of the Cisco IOS

Router Memory

Memory Volatile /

Non-VolatileStores

RAM Volatile

• Running IOS• Running configuration file• IP routing and ARP tables• Packet buffer

ROM Non-Volatile• Bootup instructions• Basic diagnostic software• Limited IOS

NVRAM Non-Volatile • Startup configuration file

Flash Non-Volatile• IOS• Other system files

Connecting to a Router

WAN Interface

AUX Port

LANInterfaces

Console USB Type B

Console RJ45

Most common methods to access the CLI: Console Telnet or SSH AUX port

Accessing a Cisco IOS Device

Console PortDevice is accessible even if no networking services have been configured (out-of-band)Need a special console cableAllows configuration commands to be enteredShould be configured with passwords to prevent unauthorized accessDevice should be located in a secure room so console port cannot be easily accessed

Console Access Method

Telnet Method for remotely accessing the CLI over a network Require active networking services and one active

interface that is configured

Secure Shell (SSH) Remote login similar to Telnet, but utilizes more security Stronger password authentication Uses encryption when transporting data

Aux Port Out-of-band connection Uses telephone line Can be used like console port

Telnet, SSH, and AUX Access

Software available for connecting to a networking device:PuTTYTera TermSecureCRTHyperTerminalOS X Terminal

Terminal Emulation Programs

Router Boot-up

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Screenshot of Loading Bootstrap

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IOS Software Configuration Modes

Primary Modes

Global Configuration Mode and specific configuration modes