A Service Probing and Channel Establishment Protocol across Multiple Network Address Translation Realms

Abstract

NAT (Network Address Translator) has been widely used to protect private networks and resolve IPv4 address depletion. All hosts behind the NAT have only private IP addresses instead of public IP addresses. Due to the nature of NAT that hides the internal network topology, a service located behind a NAT is unreachable and thus protected to some degree from the outside world. Despite some schemes have been proposed to help a host on a public network access an internal service, it is still difficult to access a service that is protected behind multiple NAT boundaries. In this paper, we propose a protocol that allows an outsider to access services protected behind disparate address realms. With the collaboration of service-probing servers, a bidirectional communication channel can be established between the outsider and the protected service. To release resource occupied by closed or dead sessions, this paper addresses the detection of channels that are no longer used. In addition, a comparison with the related work is also given in this paper.