Based on the self-adaptive multiple constraints routing algorithm (SAMCRA), an improved and exact version of our QoS routing algorithm, the tunable accuracy multiple constraints routing algorithm (TAMCRA) we have investigated QoS routing in a hop-by-hop manner because it forms the basis of IP networking as e.g. in OSPF. In particular, we studied `hop-by-hop destination based only' (HbHDBO) QoS routing that ignores the source and previous path history (as in current IP routing). We demonstrate that an exact QoS algorithm assures the avoidance of routing loops in this HbHDBO setting. However, despite the use of an exact QoS routing algorithm as SAMCRA, the exact solution cannot be guaranteed with HbHDBO routing. Fortunately, large simulation results on various sizes of random graphs show that the overall quality of the HbHDBO QoS routing is remarkably good. Finally, we show that, by using active networking as opposed to current IP routing, exact QoS routing in a hop-by-hop way can be guaranteed.