We like to have data transfer sorted by requesting IP on our local server.
For instance the following setup:

our main server IP:
clients IP on server:
client downloads a centos-iso from a centos mirror to our server (using wget).
Funny thing is that transfer occurs as 600MB on, not (the clients requesting IP)

I don't really know where the problem is: the outgoing request originating from the main server IP? iptables not setup? kernel options missing?

Input highly appreciated!