To guarantee the correct QoS, the new generation core networks are best managed by the use of a centralized server. Most of these networks use DiffServ due to its scalability, an important feature for large networks. A Bandwidth Broker architecture is a policy-based management system which purpose is to manage DiffServ networks in a centralized manner performing admission control and policy deliveries to network nodes. This paper presents the implementation of a bandwidth broker architecture for the management of QoS in DiffServ dual networks (IPv4/IPv6). This implementation, which has been programmed in JAVA, uses COPS-PR as an intra-domain communication protocol and manages the policies based on SLA/SLS preconfigured by the administrator. The performance of the proposed architecture has been tested by implementing a real IPv6 DiffServ domain testbed controlled by the developed Bandwidth Broker. The results of these tests and the corresponding conclusions are also presented.