. Core-based multicast trees use less router state, but have signi cant drawbacks when compared to shortest-path trees, namely higher delay and poor fault tolerance. We evaluate the feasibility of using multiple independent cores within a shared multicast tree. We consider several basic designs and discuss how using multiple cores improves fault tolerance without sacricing router state. We examine the performance of multiple-core trees with respect to single-core trees and nd that adding cores signicantly lowers delay without increasing cost. Moreover, it takes only a small number of cores, placed with a k-center approximation, for a multiple-core tree to have lower delay than a single-core tree with optimal core placement. We also nd that trac concentration is avoided as long as the load is spread among a set of cores. These results indicate that shared trees with multiple active cores are a viable alternative to shortest-path trees.