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Balancing Gossip Exchanges in Networks with Firewalls
J. Leitão, R. van Renesse, and L. Rodrigues

Selected sections of this report will be published in the Proceedings of the 9th International Workshop on Peer-to-Peer Systems (IPTPS '10), San Jose, CA, USA, 27 April, 2010.


Gossip protocols are an important building block of many large-scale systems. They have inherent load-balancing properties as long as nodes are deployed over a network with a ``flat'' topology, that is, a topology where any pair of nodes may engage in a gossip exchange. Unfortunately, the Internet is not flat in the sense that firewalls and NAT boxes block many peer-wise interactions. In particular, nodes that are behind a firewall can initiate communication with nodes on the public Internet, but not vice versa. This may easily unbalance the number of gossip exchanges in which nodes are involved. In particular, nodes in well connected regions of the network tend to participate in many more interactions than other nodes and may suffer from resource exhaustion.

In this paper we present and evaluate a new approach to balance gossip exchanges in networks with firewalls. Our solution requires only local information and has no coordination overhead, allowing nodes to participate in a similar number of gossip exchanges independent of the network topology.