quantum: how private net works among different host machines?

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http://serverfault.com – I'm trying to use Quantum with openvswitch plugin in my OpenStack based project. With Quantum we can create tenant private network. Now I cannot understand one thing. If my two virtual machines plug to same private network, but they locate on different host servers, how they connect to each other? According to Quantum, I think private network connects br-int, but when we create br-int, we doesn't attach br-int to physical NIC. So, how two VMs locating on different hosts pass data over physical network? (HowTos)