Monday, April 23, 2018

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Routers and Routing Basics - Introduction to Routers

Internetwork Operating System

• Like any computer, networking devices need an operating system to function.

– Workstations use UNIX, Windows, Mac OS.

– Cisco routers and switches use Cisco IOS.

• IOS core generally uniform across most routers and Catalyst switches.

• Cisco IOS utilises a command line interface (CLI), accessed by:

– Console session via a local serial connection.

– Auxiliary session via remote dial-up connection.

– Virtual terminal session via remote IP connection.

How to use Cisco IOS

• Device modes of operation:

• Cisco IOS modes of operation:

Image is Everything

• All Cisco IOS images utilise a common core of basic configuration command structure across all supported Cisco devices.

• Different IOS images developed for different hardware platforms, each with a different software feature set.

– More features in the image requires more RAM and Flash memory in the destination device.

– Important to check the Cisco device meets the requirements of the IOS to be installed.

• Display RAM and Flash memory capacities using show version in Privileged EXEC

• Show Flash usage using show flashin Privileged EXEC

The power of IOS. Now.

• For a router to be operational, it must:

– Test the hardware for errors

• Done by Power On Self Test (POST) in ROM.

– Locate and load the Cisco IOS

• Bootstrap loads from ROM, then locates IOS image from Flashand copies it into RAM.

• As IOS loads, router hardware information is displayed, including router model, processor, amount of memory, and number and types of interfaces.

– Locate and apply the router config file

• IOS looks for config file in NVRAM.

• If there’s no config file to apply, then IOS initiates setup dialogue.

IOS QuickStart Guide

• Access to the CLI is provided at two levels:

– User EXEC: Limited router monitoring

– Privileged EXEC: Unrestricted access to all router commands

• Access restricted by use of enable secret command.

– Global configuration mode: Apply configuration changes to a router.

• Access only via Privileged EXEC mode.

• A list of available commandscan be displayed by entering ? at the CLI prompt.

• If a command is incorrectly entered at the CLI prompt, a message highlighting the error will appear.

– % Invalid input detected at '^' marker

Take Command of IOS

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