Software-defined Networking

Vorlage:Context The firmware of network switches and routers (control plane) has traditionally remained proprietary, locked and under the control of the companies that manufactured the equipment. Software defined networking (SDN) seeks to change this disposition, and to make the control plane remotely accessible and remotely modifiable via third-party software clients, using open protocols such as OpenFlow.

Thus SDN allows for

1. quick experimenting and optimization of switching/routing policies, and for
2. external access to the innards of switches and routers that formerly were closed and proprietary.

Background

Vorlage:Editorial Over the past decades Internet Protocol (IP) based networks used the notion of Autonomous Systems (AS) in order to scale and extend. Under this approach connected network junctions are able to forward datagram packets to a reasonable next hop based on partial need to know basis. This is much like how the traditional post office service operates, where a postal worker in London does not need to know all the tenants of of all the streets in San Francisco in order to choose a reasonable next hop for a letter at hand. This approach to networking is simple, resileent, and it scales, but it has strong drawbacks. For one thing it does not allow the designated destinations, or tenants in the above analogy, to move without changing their identity as far as the packet delivery service is concerned. Their topological location, which is the network interface they are attached to defines their identity. In fact, using this traditional approach to internetworking, it is very hard to be specific regarding many other identity qualities such as logical grouping, access control, quality of service, intermediate network processing, etc.

This situattion has led to the creation of numerous complementary standards by the Internet Engineering Task Force (IETF), to constantly increasing complexity of network switches and routers that from the network junctions, and to increasingly complex configuration of network interfaces in order to be able to apply identity specific networking qualities. As cloud architectures and dynamic resource allocation started to evolve, and as computer operating systems and virtual machines enabling such elasticity started to get hold, the need became apparent to evolve an additional layer of virtual networking, Software Defined Networking (SDN), which will allow network operators to be specific about network service, but without coupling these specifications with network interfaces, allowing entities to move between interfaces, without changing identity or violating specifications.

Software Defined Networking therefore is the ability to decouple network control (learning & forwarding decisions) from network topology (interfaces & how they peer)

As the notion of software defined networking evolved it became apparent that a globaly aware scalable and topology decopiled software control system will take charge of the edges of the network, and traditional topology coupled control software will continue to drive the core of the network so that scalability, interopability, high-availability, and extend ability of IP networks can be maintain. This meant that an additional mechanism for driving network hardware needs to be added for the purpose of software defined edge control, in addition to the traditional vendor specific control software which typically resides very close to this hardware. Consequently a set of commands for forwarding hardware was defined in the form of protocol termed OpenFlow. This protocol enables globally aware centralized or distributed software defined controllers to drive the network edge hardware I order to create an identity based overlay on the traditional IP core.

Access Control in SDN

Remote access to the control plane is made available to administrators or users of the network, typically with a role-based access system (RBAC) in order to provide security.

Decoupling between data plane access and control plane access

In one configuration of SDN, the network control plane hardware can be physically decoupled from the data forwarding plane hardware, i.e. a network switch can forward packets and a separate server can run the network control plane.

The rationale for this approach is twofold. First, the decoupling allows for the control plane to be implemented using a different distribution model than the data plane. Second, it allows the control plane development and runtime environment to be on a different platform than the traditionally low-powered management CPUs found on hardware switches and routers.

SDN requires some method for the control plane to communicate with the data plane. One such mechanism is OpenFlow which is a standard interface for controlling computer networking switches. OpenFlow is often misunderstood to be equivalent to SDN, but there is no requirement for the use of OpenFlow within an SDN.

Definition and marketing of SDN and OpenFlow is managed by the Open Networking Foundation.

The term was coined by Kate Greene.

External links

• Software-Defined Networking: The New Norm for Networks