Numbers of mobile devices are sharply increasing in recent years. To deal with this mobility tendency, Delay and Disruption Tolerant Networks (DTN) has received significant research focus. In that context, infrastructure based DTN has promising application perspectives. In this paper, we present a route caching mechanism for infrastructure based DTN communication where the infrastructure connects multiple DTN regions. Our proposed mechanism reduces flooding of DTN messages in the infrastructure significantly when message are passed through the infrastructure. We evaluated this route caching mechanism in three flooding based DTN routing protocols. Simulations on an actual urban map show that the delivery ratio of the whole network increased greatly (by 25% to 81%) as well as overhead also decreases (maximum 50%).