// Create a bridge
ovs-vsctl add-br br0
// Build up GRE Tunnel on remote host's ip = x.x.x.x
ovs-vsctl add-port br0 gre0 -- set interface gre0 type=gre options:remote_ip=x.x.x.x
In this article, the author explains more info about GRE Tunneling in details.
http://d.hatena.ne.jp/kazuya_ax/20120420/1334928361
The way for him to build GRE Tunneling is as follows:
ovs-vsctl set interface gre0 type=gre options:remote_ip=x.x.x.x options:pmtud=false