In traditional networks, the control and data plane are embedded together as a single unit. The control plane is responsible for maintaining the routing table of a switch which determines the best path to send the network packets and the data plane is responsible for forwarding the packets based on the instructions given by the control plane. Whereas in SDN, the control plane and data plane are separate entities, where the control plane acts as a central controller for many data planes.
There are many approaches that lead to the development of today’s Software Defined Networks(SDN). They are:
- Forces
- 4D approach
- Ethane
FORCES(Forwarding and control element separation):
The idea of separation of data plane(forwarding element) and control plane was first proposed by FORCES. It is said that hardware-based forwarding entities are controlled by a software-based control plane.
FORCES can be implemented in two ways:
- The forwarding element and control plane are located within the same network device
- The control element is taken off the device and placed in a separate system.
4D approach:
The 4D approach has four planes that control
- Decision
- Dissemination
- Discovery
- Data
It follows three principles:
- Network-level objectives: The objectives should be stated in terms of the whole network instead of individual devices. So that there won’t be any need to depend on proprietary devices.
- Network-wide view: Decisions should be made based on the understanding of the whole network’s traffic, topology, and events. Actions should be taken based on considering a network-wide view.
- Direct control: The control plane elements should directly be able to control the data plane elements. It should have the ability to program the forwarding table on individual devices.
Ethane: Ethane specifies network-level access of users which is defined by network administrators. Ethane is the exact forerunner of Software Defined Networks(SDN)
Principles of Ethane:
- High-level policies should inspect the network
- Routing should follow High-level policies.
- There should be a connection between packets and their origin in the network.