In the future, global networks will consist of a hierarchy of subnetworks called domains. For reasons of both scalability and security, domains will not reveal details of their internal structure to outside nodes. Instead, these domains will advertise only a summary, or aggregated view, of their internal structure, e.g., as proposed by the ATM PNNI standard. This work compares, by simulation, the performance of several different aggregation schemes in terms of network throughput (the fraction of attempted connections that are realized), and network control load (the average number of crankbacks per realized connection.) Our main results are: the minimum spanning tree is a good aggregation scheme; exponential link cost functions perform better than min-hop routing; our suggested logarithmic update scheme that determines when re-aggregation should be computed can significantly reduce the computational overhead due to re-aggregation with a negligible decrease in performance.