Internet technologies have been designed from guidelines like the robustness principle also known as Postel's law. Jon Postel's law is described as: "Be conservative in what you do, be liberal in what you accept from others." Fundamentally, it advises protocol designs to be tolerant with what they accept from the other peers. We propose to take a step back and wonder how the robustness principle could be revisited to support security requirements as well as unifying flexibility from specifications, protocol design and software implementations. Our goal would be to define a software architecture that offers the benefits of the robustness principle (i.e., efficient network services despite the presence of various software versions), while also guaranteeing that this robustness cannot be exploited by making sure that it is only used to support authentic evolution of the protocol specification.