Software-Defined Networking (SDN) decouples the control and data planes, enabling limitless possibilities for implementing services and applications on top of the network abstraction layer. The centralized controller provides a real-time view of the entire underlying network infrastructure and therefore, management of the agile network becomes more simplified. This flexibility requires online routing updates, but during these updates, consistency has to be preserved, i.e., No packet losses or unrecognized duplications should occur. Moreover, routing updates should be done on the fly in an application-seamless fashion. Where no significant irregular delays or "communication hiccups" in packet arrivals are introduced due to the (frequent) updates. In this paper we present the first seamless consistency during on-the-fly routing updates, allowing the sender to send packets in an unchanged rate during the entire process, rate that is identical to the rate prior and after the update. The main idea is to use multicast on portions of the route, i.e., To send a packet both in the old and the new routes and only when the controller verifies the establishment and operation of the specific portion of the new route, it can remove the corresponding portion from the old route.