NAT-resilient Gossip Peer Sampling

Gossip peer sampling protocols now represent a solid basis to build and maintain peer to peer (p2p) overlay networks. They provide peers with a random sample of the network and maintain connectivity in highly dynamic settings. They rely on the assumption that, at any time, each peer is able to communicate with any other peer. Yet, this ignores the fact that there is a significant proportion of peers that now sit behind NAT devices, preventing direct communication without specific mechanisms. In this paper, we propose a NAT-resilient gossip peer sampling protocol called Nylon, that accounts for the presence of NATs. Nylon is fully decentralized and spreads evenly among peers the extra load caused by the presence of NATs. Nylon ensures that a peer can always communicate with any peer in its sample. This is achieved through a simple, yet efficient mechanism, establishing a path of relays between peers. Our results show that the randomness of the generated samples is preserved, and that the connectivity is not impacted even in the presence of high churn and a high ratio of peers sitting behind NAT devices.