-protocol to and from a single controller, chosen arbitrarily by Open
-vSwitch, is given. If a switch has no controller configured, or if
+traffic to and from a single controller is output. If none of the
+controllers is configured as a master or a slave (using a Nicira
+extension to OpenFlow), then a controller is chosen arbitrarily among
+them. If there is a master controller, it is chosen; otherwise, if
+there are any controllers that are not masters or slaves, one is
+chosen arbitrarily; otherwise, a slave controller is chosen
+arbitrarily. This choice is made once at connection time and does not
+change as controllers reconfigure their roles.
+.IP
+If a switch has no controller configured, or if