"The Internet was designed around the end-to-end principle, which says that functionality should be provided by end hosts rather than in the network itself. A new study of the effect of vast numbers of middleboxes on the Internet (PDF) indicates that this is no longer the case, since far too many devices on the Internet interfere with traffic in some way. This has serious implications for network (protocol) neutrality (as well as future IPv6 deployment) since only the particular variations of TCP that they know about will pass through them."