Network simulator?

Do you know of software which is capable of emulating networking conditions such as constrained bandwidth, latency, closed ports, congestion, collision?

Platform-specific is fine, but I'd like to be able to emulate hundreds or thousands of nodes under varying network conditions.

From stackoverflow

• Fiddler can do constrained bandwidth and latency simulations.

• You could check out ns-2 or ns-3. ns-2 is a well-tested network simulator. ns-3 is the "replacement" by the same group of people.

• NIST Net can do some crazy network emulation.

• It depends on what exactly you want to simulate. honeyd let you create detailed virtual network topologies including assymetric routes, packet loss, various TCP personality for each virtual host and let you back these virtual hosts or ports with a real system or process.

  http://www.honeyd.org/

• Here is a list of free and commercial traffic shaping applications that I compiled in answer to a similar question