Abstract:This paper first introduces the principal functions of network equipment simulator. Next the essential advantages and disadvantages of several simulators are compared,and then an instruction in detail for the installation,configurations and applications of the simulator GNS3 is presented. Finally,with an example by configuring the access control list (ACL) which is based on the firewall of Cisco PIX525,the simulator GNS3 is proved feasible to be applied in network experiments.