Simulation of distributed applications and overlay net-
works is challenging. Often the results generated in simula-
tion do not match experimental results. Distributed testbeds
like Planet-Lab help to bridge the gap, but they do not offer
enough nodes to do an Internet scale evaluation. In this
paper we use a tool called TopDNS for generating realistic
topologies for simulations, using the Planet-Lab to collect
measurement data. We show, that simulation results may
differ significantly from earlier results using synthesized
topologies. We provide a data analysis to explain the
observed results and to provide a better understanding of
latency between hosts in certain DNS name spaces.