GNS3 is an alternative or complementary software tool to using real computer labs for computer network engineers, administrators and people studying for certifications such as Cisco CCNA, CCNP and CCIE as well as Juniper JNCIA, JNCIS and JNCIE. It can also be used to experiment features or to check configurations that need to be deployed later on real devices. GNS3 also includes other features like connection of the virtual network to real ones or packet captures using Wireshark. GNS3 provides a 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 Mac OS 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: