A Reflection on the Organic Growth of the Internet Protocol Stack

In the last 15 years, the Internet architecture has continued evolving organically, introducing new headers and protocols to the classic TCP/IP stack. More specifically, we have identified two major trends. First, it is common that most communications are encrypted, either at L3 or L4. And second, due to protocol ossification, developers have resorted to upper layers to introduce new functionalities (L4 and above). For example, QUIC's connection migration feature provides mobility at L4. In this paper we present a reflection around these changes, and attempt to formalize them by adding two additional protocol headers to the TCP/IP stack: one for security, and another for new functionalities. We must note that we are not presenting a new architecture, but trying to draw up what it's already out there. In addition, we elaborate on the forces that have brought us here, and we enumerate current proposals that are shaping these new headers. We also analyze in detail three examples of such trends: the Zero Trust Networking paradigm, the QUIC transport protocol, and modern SD-WAN systems. Finally, we present a formalization of this architecture by adding these two additional layers to the TCP/IP protocol stack. Our goal is triggering a discussion on the changes of the current Internet architecture.