A Multi-perspective Analysis of Carrier-Grade NAT Deployment

TL;DR

This paper provides a comprehensive empirical analysis of Carrier-Grade NAT deployment, revealing its scope, characteristics, and impact on end users through novel detection methods and data analysis.

Contribution

It introduces new methodologies for detecting CGNs and offers the first broad empirical assessment of their deployment and behavior on the Internet.

Findings

CGNs are widely deployed across the Internet.

Detected key properties and behaviors of common CGNs.

Identified impacts of CGNs on end-user connectivity.

Abstract

As ISPs face IPv4 address scarcity they increasingly turn to network address translation (NAT) to accommodate the address needs of their customers. Recently, ISPs have moved beyond employing NATs only directly at individual customers and instead begun deploying Carrier-Grade NATs (CGNs) to apply address translation to many independent and disparate endpoints spanning physical locations, a phenomenon that so far has received little in the way of empirical assessment. In this work we present a broad and systematic study of the deployment and behavior of these middleboxes. We develop a methodology to detect the existence of hosts behind CGNs by extracting non-routable IP addresses from peer lists we obtain by crawling the BitTorrent DHT. We complement this approach with improvements to our Netalyzr troubleshooting service, enabling us to determine a range of indicators of CGN presence as well as detailed insights into key properties of CGNs. Combining the two data sources we illustrate the scope of CGN deployment on today's Internet, and report on characteristics of commonly deployed CGNs and their effect on end users.