Basic GNS3 Configuration

Learn how to configure the basics of the freely available software known as GNS3.

Real World Application

In this lab you’ll be learning how to configure the basic parameters of GNS3 which is used by Free CCNA Workbook to emulate Cisco devices for training purposes.

While GNS3 is actually illegal to use in a “production environment” pe se, it can however be a great tool for configuration verification(s) and training. For all intents and purposes of this workbook, you’ll be using GNS3 to learn the in’s and outs of basic Cisco router and switch configuration.

Lab Prerequisites

  • Ensure that GNSv3 has been installed; if not then you can view Lab 1-5 to view how to install GNSv3.

Lab Objectives

  • Verify the test path’s and variables of GNS3 including Putty and working directory.
  • Configure the 3725 and 3460 Series platform(s) to use 128MB RAM (256MB Recommended) and point the platform(s) to an IOS image you specify. The following images are RECOMMENDED for the Stub Area CCNA Workbook;




c3725-adventerprisek9-mz.124-15.T14.bin
c3640-jk9o3s-mz.124-13a.bin

If you wish to use other images, you will have to manually configure them in the GNSv3 topology.

Lab Instruction

Step 1. First launch the GNS3 application for the first time and you’ll be prompted by the GNS3 Setup Wizard as shown below;

Step 2. You’ll need to configure and test path and working directories to Dynamips (The router emulator engine) you can do this by clicking the Number 1 button on the Setup Wizard prompt and you’ll be prompted with the following configuration window. Verify that the path information is correct. Putty is included in the GNS3 installer package however if you wish to use SecureCRT on Windows x64 then you’ll need to change the terminal application command string located in the “Terminal Settings” tab to c:\PROGRA~1\VANDYK~1\SecureCRT\SecureCRT.exe /T /N %d /telnet 127.0.0.1 %p

Step 3. Click on the Dynamips tab listed down the left hand side of the Preferences window and verify that the executable path and working directory is correct. Once you’ve done so click the Test button and if all configuration variables are operational you’ll receive a message next to the best button that reads; Dynamips successfully started

The Free CCNA Workbook GNS3 topology uses the Cisco 3725 and 3640 router(s). Before continuing, obtain the images listed in the prerequisites and open the images using WinRAR and extract the decompressed image to \gns3\images\

Step 4. After Dynamips can start successfully, exit the GNS3 preferences window back to the GNS3 Setup Wizard. Now that the operational variables are correctly configured you’ll need to configure the baseline configuration for the routers to be utilized by GNS3. Click on the Number 2 box in the GNS3 Setup Wizard to launch the IOS Images and Hypervisors Configuration window. You’ll need to configure the 3725 and 3640 platforms with a minimum of 128MB RAM and point the platforms to the correct decompressed image that you’ve placed into in \gns3\images\


Please note that the latest Free CCNA Workbook GNS3 topology requires that the the Hyper-visor Memory Usage Limit be changed to 2048, you can do this by clicking the Hyper-visor Manager tab when you’re in the Dynamips Configuration Tab in GNS3 preferences.

Step 5. Once you have configured the two platforms as required per the Stub Area Networking topology (as shown below) you can exit the IOS and Hyper-visor Configuration window and exit the GNS3 Setup Wizard then you are ready to proceed to the next lab which entails importing the Stub Area Networking GNS3 topology configuration.