Dynamips emulates Cisco 7200/3600/3725/3745/2600/1700 Routers on a traditional PC. You can use dynamips to create labs. It uses IOS Images (which are not part of this package). Of course, this emulator cannot replace a real router.

It is simply a complementary tool to real labs for administrators of Cisco networks or people wanting to pass their CCNA/CCNP/CCIE exams. For a Command Line Interface for dynamips see dynagen or gns3 package.