Let’s turn our focus to Linux users now. Our examples will use Ubuntu. Anyone can download Ubuntu from www.ubuntu.com for free – it just may take a while since it’s a large file. Performance is somewhat better in a Linux environment.
Step 1 – Install GNS3
Option A – Install GNS3 using Ubuntu Software Center
For Ubuntu version before 11.10, open the Synaptic Package Manager. Go to the System menu, then Administration, and finally Synaptic Package Manager. For later versions, open the Ubuntu Software Centre, which you should find in the left pannel.
Use the Search box and type gns3 followed by a return.
When you find gns3 software, you can use the install option. Ubuntu will then download and install gns3 and all its dependencies for you.
Option B – Run GNS3 from the sources
Usually the GNS3 version available in Ubuntu Sofware Centre is not the latest one. If this is the case with your version of Ubuntu, you can choose to run GNS3 from the sources. However you still need to install GNS3 dependencies using the Ubuntu Software Centre in the same way as option A but this time search and install python-qt4 software. Once the dependencies are installed, you can run GNS3 from the souces, first start to download a source archive. You may choose any of the source archives for Linux. For this example we will use GNS3-0.7.4-src.tar.gz. Next, right-click on the file, GNS3-0.7.4-scr.tar.gz, and choose Extract Here. You’ll see a new icon labeled GNS3-0.7.4-src.
Now we need to download the latest Dynamips binary for Linux, here we will use dynamips-0.2.8-RC3-community-x86-bin. Put this file in the GNS3-0.7.4-src directory. Before you can use dynamips you must change the Dynamips permissions to allow execution. Right-click on dynamips-0.2.8-RC3-community-x86.bin and choose Properties. Click on the Permissions tab, and then click the box next to Execute: Allow executing file as program in order to place a check mark in it. Then click Close.
Step 2 – Configuring GNS3
Double-click the gns3 icon to start the application. Click the Run button. If this is the first time you use GNS3, the Setup Wizard begins. Click on the big number 1 to open the Preferences window (actually located under the Edit menu in GNS3). Then click Dynamips in the left-hand pane. Click the ellipses next to Executable path and then click dynamips-0.2.8-RC3-community-x86.bin followed by the Open button. When you return to the Preferences screen, click Apply followed by the Test button. If everything is right you should see a green message indicating that Dynamips has successfuly started.
Now click OK to return to the Setup Wizard. Click the big number 2 to open the IOS images and hypervisors window (actually located under the Edit menu in GNS3).
In the IOS images and hypervisors window, use the ellipses button next to the Image file box to locate an IOS image. As mentioned earlier, you must provide your own Cisco IOS to use with GNS3 due to licensing issues. GNS3 is meant to be used in a lab environment for testing and learning. Once you have obtained your own copy of a Cisco IOS for one of the supported platforms, you are ready to continue. Supported platforms are Cisco 7200, 3600 series (3620, 3640 and 3660), 3700 series (3725, 3745) and 2600 series (2610 to 2650XM, 2691).
The file will appear as your Image file. Next, click the drop-down arrow next to Platform and choose the platform that corresponds to your IOS file. Now click the drop-down arrow next to Model and choose the model corresponding to your IOS file. Then click the Save button followed by the Close button. You’ll return again to the Setup Wizard window. Click OK to finish.
Now it’s time now to create our first simple topology. So whether you are a Windows user or a Linux user, continue to the next section. We have often used screen shots from Windows when describing GNS3 usage, but the screen shots from Linux would look identical except for the title area. It’s time to create our very first simple topology.