GNS3

Graphical Network Simulator

Over View

• GNS3 is a Graphical Network Simulator that allows

emulation of complex networks.

• GNS3 allows the same type of emulation using Cisco

Internetwork Operating Systems. It allows you to run a

Cisco IOS in a virtual environment on your computer.

• Dynamips is the core program that allows IOS emulation.

Dynagen runs on top of Dynamips to create a more user

friendly, text-based environment.

Get Start with GNS3

Download GNS3.

http://www.gns3.net

The easiest way to install GNS3 in a Windows environment is to use the

top file: GNS3-0.5-win32-all-in-one.exe.

Defining Cisco IOS files

You must provide your own Cisco IOS to use with GNS3 due

to licensing issues.

Current platforms supported include:

Defining Cisco IOS files - Continuous

On the Edit menu, choose IOS image and hypervisors.

Defining Cisco IOS files - Continuous

Under the IOS Images tab, click and then find your

Cisco IOS file and click Open.

Using Cisco IOS Decompressed

Using Cisco IOS Decompressed- Continue

Using Cisco IOS Decompressed- Continue

• Choose the folder which you will extract to.

• Next, find the file you had extracted, then rename this extend

file from .bin to .image

GNS3 Main Interface

GNS3 Main Menu

Drop-down menu from right-clicking on a router:

Calculating Idle PC

Calculating Idle PC

Right-click the router and choose Start.

Calculating Idle PC

Right-click the router again and choose Console.

A telnet console opens up.

Calculating Idle PC

Observe CPU usage in Windows, by pressing Ctrl+ALT+DEL and choose

Task Manager. Click on the Performance tab to view CPU usage.

You will observe CPU usage will

be at or near 50%.

Calculating Idle PC

To reduce CPU usage, right-click on

Router and choose Idle PC. GNS3 will

spend a moment calculating an Idle PC

value before presenting the screen to

the right.

If you click the drop-down arrow, you

see a list of possible idlepc values.

Potentially better idlepc values are

marked with an asterisk.

Choose one of the values and click OK.

Calculating Idle PC

You may repeat this process to find the value that reduces

CPU usage the most.

The best ideal is CPU usage

around 5 – 7 % per router

Building Topology

• Start GNS3. Drag routers running an IOS you have configured into the

workspace.

Right-click each router and

choose Configure.

On Node Configuration

Panel click Slot.

On Slot Drop-Down, choose

the type interface you want.

Building Topology

Click on Add Link, and choose Manual

Building Topology