A Bottom-Up Investigation of the Transport-Layer Ossification

Recent years have seen the rise of middleboxes, such as NATs, firewalls, or TCP accelerators. Those middleboxes play an important role in today’s Internet, and are now extensively deployed in various networks including corporate networks, Tier-1 ASes, cellular networks, and WiFi hot-spots.Unfortunately, despite the added value that they bring to networks, they radically change the transport paradigm from the legacy end-to-end principle, and drive increasing complexity in the path. The consequences of these changes are a wide variety of simple to subtle impairments to protocols and features, that in turn lead to the ossification of the network infrastructure. While the latter is now a well-known problem, its causes are not that much understood.To fill this gap, we provide a more detailed explanation of the factors of the transport-level ossification, and we give insights on their prevalence in the wild. We extract path conditions by processing a large collection of observations of middlebox in-path packet manipulations, and we categorize the observed transport impairments based on the complications that they engender. We show that more than one third of network paths are crossing at least one middlebox, and a substantial percentage are affected by feature or protocol-breaking policies. Finally, we show that the majority of the devices that implements them are located in edge networks.