In a peer-to-peer network, nodes are typically required
to route packets for each other. This leads to a problem
of “free-loaders,” nodes that use the network but refuse to
route other nodes’ packets. In this paper we study ways of
designing incentives to discourage free-loading. We model the
interactions between nodes as a “random matching game,” and
describe a simple reputation system that provides incentives for
good behavior. Under certain assumptions, we obtain a stable
subgame-perfect equilibrium. We use simulations to investigate
the robustness of this scheme in the presence of noise and
malicious nodes, and we examine some of the design trade-offs.
We also evaluate some possible adversarial strategies, and discuss
how our results might apply to real peer-to-peer systems.