  In recent years, many DHT-based P2P systems have been proposed, analyzed, and
certain deployments have reached a global scale with nearly one million nodes.
One is thus faced with the question of which particular DHT system to choose,
and whether some are inherently more robust and scalable.
  Toward developing such a comparative framework, we present the reachable
component method (RCM) for analyzing the performance of different DHT routing
systems subject to random failures. We apply RCM to five DHT systems and obtain
analytical expressions that characterize their routability as a continuous
function of system size and node failure probability. An important consequence
is that in the large-network limit, the routability of certain DHT systems go
to zero for any non-zero probability of node failure. These DHT routing
algorithms are therefore unscalable, while some others, including Kademlia,
which powers the popular eDonkey P2P system, are found to be scalable.
