Is there a Cisco IOS Virtual Appliance?

Need to do test configurations on (unfamiliar) Cisco/IOS equipment. Is there a virtual machine I can light up and use it in my test environment as a real firewall/edge/core router?

From serverfault gravyface

• Have a look at GNS3 it's a nice GUI frontend to Dynamips which is a IOS router simulator.

  Kyle Brandt : Might give GNS3 a try again but gave me a bunch of trouble last time I used it, now I just use dynamips with dynagen.
  From 3dinfluence

• The only Cisco equipment emulator I know of is Dynamips/Dynagen, but its purpose is learning Cisco IOS commands for certification exams, not testing actual networking setups. While you could certainly do that, the performance would be likely very bad. Even connecting two routers on the same machine eats a lot of CPU, and you have to play around to find which idleCPU value works for the image you are using, to get lower CPU usage, when the router is idle. Otherwise even with idle routers you get high CPU usage.

  This is in contrast to Juniper Olives, which have quite good performance.

  gravyface : wish I could mark you both right, so I +1'ed 3dinfluence and gave you the correct answer. You need the points more than him anyways. :)

  Kyle Brandt : Performance is a good point, I am testing some QoS/rate-limiting setups and can't push more than ~5M through one of them. So I am just scaling down my 10M lab to a 1M lab by dropping a digit :-)

  Prof. Moriarty : @gravyface LOL, funniest most thoughtful comment I read so far. Thanks!
  From Prof. Moriarty