Hic sunt NATs: Uncovering address translation with a smart traceroute

Middleboxes are pervasive in today's Internet as they are deployed for an increasing number of reasons. An example is the network address translation (NAT), one of the first task to be performed to cope with the lack of IPv4 addresses. Recently the landscape for NATs has become even more crowded, especially in mobile networks, mainly due to the impossibility of IPv6 to be a large-scale solution to addressing issues. In this paper, we present a novel methodology for detecting NATs embodied in Mobile Tracebox, a measurement tool for Android smart devices that detects a wide range of middle-boxes. It analyzes ICMP time-exceeded messages received during traceroute and points at IP and transport checksum inconsistencies in the embedded packets to uncover address translation along a path. We deployed Mobile Tracebox through a crowdsourcing approach and used the collected dataset to validate our methodology. Results showed that, in absence of middleboxes breaking traceroute, it can help to detect and locate NATs in the majority of the cases.