GNS3 is a graphical network simulator that allows you to design complex
network topologies. You may run simulations or configure devices ranging from
simple workstations to powerful Cisco routers. It is based on Dynamips, an IOS
emulator which allows users to run IOS binary images from Cisco Systems and
Pemu, an PIX firewall emulator based on Qemu.

Homepage:
https://github.com/GNS3/gns3-server
