What is GNS3?

What is GNS3?

GNS3 (Graphical Network Simulator) is an open source software that simulate complex networks while being as close as possible to the way real networks perform. All of this without having dedicated network hardware such as routers and switches.

This software provides an intuitive graphical user interface to design and configure virtual networks, it runs on traditional PC hardware and may be used on multiple operating systems, including Windows, Linux, and MacOS X.

In order to provide complete and accurate simulations, GNS3 actually uses the following emulators to run the very same operating systems as in real networks:

Dynamips, the well known Cisco IOS emulator.

VirtualBox, runs desktop and server operating systems as well as Juniper JunOS.

Qemu, a generic open source machine emulator, it runs Cisco ASA, PIX and IPS

Who can use it?

GNS3 is an excellent alternative or complementary tool to real labs for network engineers, administrators and people studying for certifications such as Cisco CCNA, CCNP and CCIE as well as Juniper JNCIA, JNCIS and JNCIE. Open source networking is supported too.

It can also be used to experiment with features or to check configurations that need to be deployed later on real devices.

Their programs includes exciting features, for instance connection of your virtual network to real ones or packet captures using Wireshark.

GNS3 combines the best features of existing emulation software (such as Dynamips and Qemu) into a GUI interface and allows you to create an unlimited number of Cisco routing-and-switching lab scenarios. Because truly learning about routing and switching requires some hands-on practice — and again, most people and companies can’t afford to invest in all of the equipment necessary to test dozens of different scenarios — GNS3 is a viable option. You do not need to customize the software at all, and can work within the main window to drag and drop different network components such as routers, firewalls, switches, etc., into your networking area, and then try different connections between them that meet your network standards.

Best of all, GNS3 is free. The open-source software is compatible with all Windows machines, and comes in a bundle that includes additional tools such as Putty, SuperPutty, Wireshark, and WinPcap. You can also access a free license for a Solarwinds toolset; knowing how to use Solarwinds is becoming a more important skill, so it’s worth checking out what GNS3 has to offer.

GNS3 is a godsend to anyone who needs to test different network configurations as preparation for a certification exam or who is building a new network from the ground up. However, there is a slight catch: GNS3 comes with a pretty steep learning curve. If it’s going to be of any use to you at all, you need to learn how to use GNS3 software. In fact, some engineers have noted that the software requires fairly advanced networking knowledge if you are going to get the most from it. If you are a beginner, not only is there the potential for frustration, but there is also a chance that the software can bog down your computing resources if you do not configure and run it appropriately.

Another issue for GNS3 users is the fact that you will have to supply your own IOS image in order to import the correct IOS software for the router you are emulating. Also, because GNS3 does not support full switch functionality or switch IOS images, you will have to configure your router with NM-16ESW switch modules. The good news is that even with these limitations, you can still do the majority of what you need to do for your network — and if you do have access to actual Cisco switches, you can connect your GNS3 software to those switches and include them in your simulations.