I have the following entry in parent.config. 

dest_domain=.     parent=";"     round_robin=true

  I expect the alternate requests will be send to port :4000 and :4001 so as to load balance the request. But I noticed that for all packets are sent through 4000 only. ( I have tunnels created from my machine to ATS machines in two other machines. :4000 port is opened to ATS in one machine and :4001 port is opened to ATS is another machine.)  What could be the problem and how do I debug this issue further ?