A Measurement of NAT & Firewall Characteristics in Peer to Peer Systems

NATs and firewalls break the original model of IP end-to-end connectivity across the Internet, since their presence creates a new Internet architecture made of many private networks. This architecture, designed upon the client/server model, introduces complications in communication between hosts and has performance impacts, especially for P2P protocols, since hosts outside a private network are not able to initiate a connection to hosts inside that private network. In this paper we present a study of the current distribution and characteristics of the NATs and firewalls existing in the Internet, with respect to UDP communication. We believe that our study provides valuable insights for the development of P2P systems that intend to address the NAT/firewall issue effectively.