GNS 3

GNS-3 is a graphical network simulator GNS-3 is a graphical network simulator which allows you to design and create complex network topologies. You may run simulations, or configure each device, from a simple workstation to a powerful Cisco router.

To allows complete simulations, GNS-3 is based on two existing projects:
NS-3 , a discrete-event network simulator for Internet systems, targeted primarily for research and educational use.
Dynamips, an IOS emulator which allows users to run IOS binary images from Cisco Systems.

GNS-3 is an open source product that may be used on multiple platforms, including Windows, Linux, and MacOS X.

Here are some key features of "GNS 3 ":
Design of high quality network topologies.
Emulation of Cisco routers.
Load-balancing on multiple hosts/hypervisors when in emulation mode.
Topology import and export.
Image exports (PNG, JPEG, BMP, XPM).


Requirements:
Qt >= 4.2
Python >= 2.4
Sip >= 4.5 if you need to compile PyQt
PyQt >= 4.1