Network stressing software

[IHateMyJob2004]

Is anyone aware of some free software than can "flood" a network with packets? Just something that constantly sends out TCP and preferably UDP messages?

I found a program called Heavy Load which claims to be used for stressing networks and more. I am apprehensive about installing it however.

So, does anyone have a good program that they are aware of? Or is heavy Load acceptable?

Thanks.

UPDATE 1: heavy Load is not what I want. It doesn't do anything with the network as it claims to.

 

[quikah]

http://www.netperf.org/netperf/

 

[tranceport]

I use http://dast.nlanr.net/Projects/Iperf/