Jay Ann 3 (GNS3) is an open source software simulator complex network that tries to, where possible, to the network, real close and to the hardware, the physical network does not need. Has a graphical environment for the construction of complex networks. Program GNS3 based on the code Dynamips written, and this possibility provides to be able to be IOS, Cisco instead of running on expensive equipment, Cisco, etc. on the computer run.