Is it possible to slow down the network interface?

[Yuri]

For the testing purposes, I would like to be able to control the maximum 
speed of the interface.
There is this command 'ifconfig re0 media 10baseT/UTP' that is supposed 
to lower the speed to 10Mbps. However, it makes interface unusable on my 
system. All connections are broken, even the router had to be rebooted. 
Maybe this is the router issue.

Is there any other, "soft" way to change maximum interface speed to a 
particular value?
When somebody sends data too fast, OS sends back ICMP notifications that 
connection is jammed. My question is, is it possible to impose such 
condition artificially?
Is 'ifconfig re0 media 10baseT/UTP' actually supposed to work 
transparently, or disconnects are to be expected?

Yuri