Evaluating the Impact of Path Brokenness on TCP Options

In-path network functions enforcing policies like firewalls, IDSes, NATs, and TCP enhancing proxies are ubiquitous. They are deployed in various types of networks and bring obvious value to the Internet.

Unfortunately, they also break important architectural principles and, consequently, make the Internet less flexible by preventing the use of advanced protocols, features, or options. In some scenarios, feature-disabling middlebox
policies can lead to a performance shortfall. Moreover, middleboxes are also prone to enforce policies that disrupt transport control mechanisms, which can also have direct consequences in term of Quality-of-Service (QoS).

In this paper, we investigate the impact of the most prevalent in-path impairments on the TCP protocol and its features. Using network experiments in a controlled environment, we quantify the QoS decreases and shortfall induced by feature-breaking middleboxes, and show that even in the presence of a fallback mechanism, TCP QoS remains affected.