GNS3 is a graphical network simulator to check the complex networks without real hardware, we can simulate Cisco devices and Juniper devices in it.

This program is very useful for Network Administrators who is working in real networks and those who is studying for Cisco exams like CCNA, CCNP and CCIE.

This program is a open source freeware and works with Windows, Linux and MAC OS X.

The main features of this wonderful program:

  • Ability to design high quality and complex networks
  • test the working of a newer designed network before deploying in real time environment.
  • Emulation of various Cisco and Juniper devices.
  • Interoperability with real time networks.

You can download GNS3 from here

Useful tutorials about how to setup a CCNA Voice lab with GNS3 and VMWARE can be found here and a pdf tutorial about how to use GNS3 with windows can be downloaded from here