In an effort to rethink network str

In an effort to rethink network structure, clean-slate projects surfaced, drawing inspira
tion from the preceding innovations and suggesting an entirely new perspective. With past
experience and current knowledge in mind, researchers approached network design from the
ground up. An influential formulation of the new way of thinking has been the 4D archi
tecture [11]. 4D centres around 3 key principles which depart from the decentralised and
low-level perspective. It encourages a network-wide view and global objectives enforced by
routing elements directly controlling the entire domain. The network itself is divided into
the 4 ”D” planes. A Discovery Plane estimates the capabilities of the network and provides
the information to the Decision Plane. In the spirit of the new paradigm the decision plane
regulates the network and configures the devices of the Data Plane, which processes and
forwards packets. Providing a logical and separate channel, the Dissemination Plane is the
point of connection between the two planes, comparable to the open interface in ForCES.
4D is not a practical solution but a proposal for a new approach and provided incentive
to redesign the network. Building on the design principles established by the clean-slate project, a Stanford team developed SANE [33]. Intended to be a feasible implementation of
the concept in enterprise networks, the framework implements a single protection layer con
taining servers which enforce global security and access policies. ETHANE [34] extended the
work of SANE and introduced a centralised controller and specialised ETHANE switches.
The controller communicates with the switches and updates their flow tables according to
an administrator policy. In contrast to routing tables, a flow-based system does not route
based on destination of IP and MAC addresses but rather matches the header fields against
pre-existent table entries and forwards the packet out on the specified port. As the protocol
does not operate based route calculations, the view of the devices is reduced to their own
structure. From the view of the controller a continuous traffic flow travelling over generic
network nodes is created. ETHANE was successfully deployed in the Stanford computer
science department and paved the way for the next step in Software-Defined Networking,
known as OpenFlow [3]. The research and building stones of the past years eventually
culminated in the publication of this protocol, which was heavily inspired by ETHANE.