In this paper we present a comprehensive, yet simple, extension to the existing systems used for Digital Contacts Tracing in Covid-19 pandemic. The extension, called BAC19, will enable those systems, regardless of their underlying protocol, to enhance their sets of traced contacts and to improve global fight against pandemic during the phase of opening boarders and enabling more traveling. BAC19 is a structured overlay network, or better, a Federation of mathematical Distributed Hash Tables. Its model is inspired by the Chord and Synapse structured overlay networks. The paper presents the architecture of the Overlay Network Federation and shows that the federation can be used as a formal model of Forward Contact Tracing.