GNS3 is graphically network simulator which you can use in the absence of physical routers and switches.
GNS3 helps you in complex real lab scenarios for every one in the feild of networking beginers and experts. It is providing great benefit for certifications if you are studying like in Cisco
CCNA,CCNP in security or voice leading to CCIE, as well as Juniper JNCIA, JNCIS and JNICE.
GNS3 is very easy to use, for this you have to use real Cisco IOS and Juniper JunoS for labs configuration. There are different versions availabe for GNS3 in different Operating Systems. As it is an open source program so different version for Windows,Linux and MacOS X are available. You can use many softwares and applications which are already being used to integrate with real routers and switch, now even you can integrate them with GNS3. Other most common applications like VMWare and VirtualBOX which are used for the many diffenet labs scenarios.
This blog will help you for some usefull information and videos regarding GNS3 related to Cisco and JUniper in different lab scenarios.
