Some embodiments provide a method for forwarding data messages between edge nodes that perform stateful processing on flows between a logical network and an external network. At a particular edge node, the method receives a data message belonging to a flow. The edge nodes use a deterministic algorithm to select one of the edge nodes to perform processing for each flow. The method identifies a first edge node to perform processing for the flow in a previous configuration and a second edge node to perform processing for the flow in a new configuration according to the algorithm. When the first and second edge nodes are different, the method uses a probabilistic filter and a stateful connection tracker to determine whether the flow existed prior to a particular time. When the flow did not exist prior to that time, the method selects the second edge node for the received data message.