Two challenges of Software Networking: Name-based Forwarding and Table Verification. (Deux défis des Réseaux Logiciels : Relayage par le Nom et Vérification des Tables)

ion and modularity In the field of the Computer Science, abstraction and modularity are commonly used. The term abstraction indicates the definition of a certain software component specifying only the interface showed to the users. Programmers can therefore make their own design and implementation choices, as long as they respect the external interface. As an example, we can consider the abstract data type of a “List”, which is a set of elements that allows insert and remove operations. The abstract model of the List describes its behavior, that is storing elements without particular ordering and providing “add” and “remove” mechanisms. The List can be implemented in several ways (using arrays, linked nodes, or even with a dictionary), but all those implementations are compatible as they share the same user interface. Moreover, when programs consists of many millions lines of codes, they are built usingmodular programming. Rather than building a huge monolithic application, developers today tend to build modular software, usually with a main software core and multiple ad-hoc modules. Such a software is easy to be upgraded, because the core is stable and new modules may be added when needed. Software evolution is much easier when modularity is preserved. SDN brings the notions of abstraction and modularity to the network. Programmers can implement their own network instance, and it can be made of several modules, fully upgradeable on the fly. Flexibility is one of the main advantages of those features. Virtualization Network virtualization is the coexistence of multiple virtual network instances sharing the same physical infrastructure. In other words virtual networks are a set of virtual nodes and virtual links, mutually independent and logically separated, built on top of real nodes and real links [CB10]. This approach is similar to the homologous equivalent in servers: several computer instances rely on the same physical architecture, but they are logically separated and independent. Many technologies are currently used to implement virtual networks, and they are located at different levels of the protocol stack: a Virtual Private Network (VPN) is a virtualization technique implemented on top of IP/MPLS networks, and therefore it belongs to the layer 3 [RR06]; a Virtual LAN (VLAN) consists of a set of switches that may virtualize physical links using a special field in the layer 2 Ethernet frame [TFF13]; there are even layer 1 virtualization techniques, using L1 protocols such as SONET or SDH [TIAC04]. Software-Defined Networking 32 SDN plays a major role in improving existing virtualization mechanisms. There are two main advantages in SDN-based network virtualization [JP13]. The first one is the ease of deployment: thanks to the simplified data plane and the centralized software programmability, it is easy and fast to install several network instances at different locations of the network without requiring ad-hoc hardware or protocols. Finally, as SDN switches are simple standard devices while the intelligence resides in the centralized controller, they are expected to be cheaper than current devices where the control is distributed on each equipment. Network Functions Virtualization, or NFV [C12, HGJL15], is a further decoupling of network functions from the dedicated hardware devices (similarly to Virtual Machines in virtualized servers). While SDN virtualization mainly focus on network resources, NFV aims to abstract the functions implemented by network devices (e.g. firewalls, packet filters, DNS servers) and relocate them as generic boxes to be deployed anywhere in the network infrastructure. NFV may work in conjunction with SDN by providing the abstract infrastructure (Data plane) that is orchestrated by the SDN controller (Control plane). Furthermore, a generic SDN/NFV network may be thought as a set of virtual network instances where the abstract virtual functions may deployed as simple network virtual devices, all sharing the same physical infrastructure. Interoperability When the network behavior is software-defined, the definition of network instances becomes similar to programming a computer, providing a gain in terms of flexibility and ease of management. Furthermore, when the APIs between the Software and the Hardware sections are open and publicly available, every vendor may decide to adopt such a model, giving a great improvement in the interoperability. Network owners are not restricted to use vendorcompatible hardware, and vendors might also acquire some market slices thanks to the increased competition available.