I am not aware of simulation tool. But you can have real network = not simulation. You can test new features and old features, you can test real bugs  Much better IMHO.
thank for you replay.. i was mean SIM LAB, as you know cisco has examination CCNA , and it has LAB SIM topology for OSPF, EIGRP,RIP......etc, help the student to prove skills , it working on Packet trace .
