NATwatcher: Profiling NATs in the Wild.

NATs are commonplace in the Internet nowadays. It is fair to say that most residential and mobile users are connected to the Internet through one or more NATs. As with any other technology, NAT presents upsides and downsides. Probably the most acknowledged downside of the NAT technology is that it introduces additional difficulties for some applications such as peer-to-peer applications, gaming, and others to function properly. This is partially due to the nature of the NAT technology but also due to the diversity of behaviors of the different NAT implementations deployed in the Internet. Understanding the properties of the currently deployed NAT base provides useful input for application and protocol developers regarding what to expect when deploying new applications in the Internet. The goal of this article is to identify common NAT profiles in order to provide an overview of the current behavior of NATs. We develop NATwatcher, a tool to test NAT boxes using a crowdsourcing- based measurement methodology. We perform a large measurement campaign using NATwatcher recruiting over 700 users, from 65 different countries and 280 ISPs. We present the results after testing and profiling NAT products from over 120 vendors.