GNS3 is a graphical network simulator that allows you to design complex network topologies and to launch simulations on them.
To allow complete simulations, GNS3 is strongly linked with :
* Dynamips, an IOS emulator which allows users to run IOS binary images from Cisco Systems.
* Dynagen, a text-based front-end for Dynamips.
GNS3 is a excellent complementary tool to real labs for administrators of Cisco networks or people wanting to pass their CCNA, CCNP, CCIP or CCIE certifications.
I created a few video tutorials for GNS3 using Windows and Linux.
http://www.blindhog.net/category/gns3/
Enjoy
