  We present the study of the linear conductance vs.\ applied gate voltage for
an interacting six site ring structure, which is threaded by a flux of $\pi$
and coupled to a left and a right lead. This ring structure is designed to have
a vanishing conductance for all gate voltages and temperatures provided
interactions are ignored. Therefore this system is an ideal testbed to study
the interplay of interaction and interference. First we find a Kondo type
resonance for rather large hopping parameter. Second, we find additional
resonance peaks which can be explained by a population blocking mechanism. To
this end we have to extend the Kubo approach within the Density Matrix
Renormalization Group method to handle degenerate states.
