1. A computer-readable medium for operating a controller on a network, wherein the instructions, when executed by one or more processors, cause the one or more processors to perform operations comprising: implementing a transition protocol in which a first rule set for routing packets received by a group of switches during a first time period is to be updated to a second rule set, wherein implementing the transition protocol includes: during a first transition period, implementing a transition rule set in which (i) any switch in the group of switches that is to forward packets to a same given node under both the first rule set and the second rule set will continue to forward packets to the given node during the first transition period, and (ii) any switch in the group of switches that is to forward packets to a node under the second rule set that is different than a node that the switch forwarded packets to under the first rule set will forward packets to the controller; during a subsequent time period following the first transition period, sending packets received from any switch in the first transition period to a destination node in accordance with the second rule set, and implementing the second rule set for each switch in the group of switches.