I use NeSSi2 (Network Security Simulator) its open source project. Its capabilities such as profile-based automated attack generation, traffic analysis and support for the detection algorithm plugins allow it to be used for security research and evaluation purposes.
NeSSi² is an open source project developed at the DAI-Labor and sponsored by Deutsche Telekom Laboratories. Its
a novel network simulation tool which incorporates a variety of features relevant to network security distinguishing it from general-purpose network simulators. Its capabilities such as profile-based automated attack generation, traffic analysis and support for the detection algorithm plugins allow it to be used for security research and evaluation purposes.
It has been successfully used for testing intrusion detection algorithms, conducting network security analysis, and developing overlay security frameworks.
Also Network Attack (NETA) a framework in OMNET++ is used to simulate all security based projects in network by the Research scholars.