An intra-domain Quality of Service (QoS) routing protocol for the Differentiated Services framework is being developed at the University of Coimbra (UC-QoSR). The main contribution of this paper is the evaluation of the scalability and stability characteristics of the protocol on an experimental test-bed. The control of protocol overhead is achieved through a hybrid approach of metrics quantification and threshold based diffusion of routing messages. The mechanisms to avoid instability are: (i) a class-pinning mechanism to control instability due to frequent path shifts; (ii) the classification of routing messages in the class of highest priority to avoid the loss of accuracy of routing information. The results show that a hop-by-hop, link-state routing protocol, like Open Shortest Path First, can be extended to efficiently support class-based QoS traffic differentiation. The evaluation shows that scalability and stability under high loads and a large number of flows is achieved on the UC-QoSR strategy.