The State of ECN Adoption in the Internet

Explicit congestion notification (ECN) is a signaling mechanism that enables a router along the network path between a sender and receiver to mark packets for signaling incipient congestion. More than a decade ago, Bauer et al. characterized the extent of ECN adoption on the Internet and a few years later Trammell et al. extended that analysis. Since then, the Internet has evolved substantially. Today, most operating systems support ECN, IPv6 has been widely deployed, and new technologies that build on ECN, such as L4S, have emerged. These changes naturally motivate the need to revisit the study of ECN adoption. We, hence, revisit and extend the two key ECN characterization efforts. We find that the majority of Internet service infrastructures are ECN-aware, although a nontrivial fraction of hosts, routers, and middleboxes bleach ECN bits. Many hyper-giants, unfortunately, bleach ECN bits along the path, which has substantial implications for the use of technologies such as L4S. In this study, we also note that IPv6 endpoints and paths generally show stronger support for ECN than those using IPv4.