In this paper, we consider production-distribution systems with buffer and capacity constraints in the presence of unknown inputs. We face the problem of finding a control that drives the buffer levels to a prescribed value. We consider a continuous-time model and we show that some important properties hold which generally fail in the discrete-time case. In particular, we show that the case in which the controller knows the external input is equivalent to the case in which such information is not available. Furthermore, a decentralized strategy can be devised. We also show that in the case of network failures, the controller does not need to know the current network configuration in order to guarantee its tracking goal as long as a certain necessary and sufficient condition is satisfied.