Analysis and topology-based traversal of cascaded large scale NATs

Abstract

Middleboxes are an essential part of today's networks since they allow to introduce additional functionality without having to change end-hosts. Network Address Translation (NAT) has been the number one choice for coping with the address depletion problem of IPv4. Although NAT introduces many problems for existing applications it can be found in almost every consumer and mobile network. Large Scale NAT (LSN) is the latest trend in middlebox deployment and plays an important role for the transition from IPv4 to IPv6. LSN may consist of a distributed NAT at the provider or it may include multiple layers of NAT. LSN introduces additional problems for customers since many existing NAT traversal techniques cannot be applied. This paper presents an approach for discovering and measuring stateful cascaded NATs on the path between two arbitrary peers in the Internet. An algorithm combining multiple UDP packets, individual timeouts and traceroute measurements is presented and evaluated in a public field test. Finally, we show how NAT traversal for LSN can be improved by parameterizing existing algorithms according to the detected topology.