SDN: Introduction, Working, Architecture
5. The Open Flow Protocol
The transfer is simplified by removing the old control plane and centralizing control plane management. OpenFlow is a common control plane standard used in Operation Technology SDN, making it interoperable with other SDN solutions. The difference is that OpenFlow is the only control plane in the switch, and the switch retains through power cycles, and all flows and redundancy are proactively traffic-engineered so the switches can perform the forwarding they are configured to do with or without telecommunications.
Network control and forwarding operations are decoupled in SDN designs, allowing network control to be directly programmable and the underlying infrastructure to be distinct from applications and network services.
5.1 OpenFlow enabled Switch Architecture
To define a path from source to destination OpenFlow offers a programmatic control of flows to the network administrators. It allows a way to remove the overhead of routers packet processing for defining the path, and network management costs while escalating a network. In an OpenFLow architecture, the entire system consists of many Open-Flow enabled devices, which are managed by one or more OpenFlow controllers. Again the OpenFlow devices use one or more flow tables. A flow could be a set of packets with same MAC IDs or IP addresss, packets with the same VLAN tag or packets are arriving from the port. An abstract model of OpenFlow switch is depicted in Fig below. Flow table consists of flow entries, which decides how the packet will be processed or forwarded of a particular flow. Each flow entries in the table have three fields: match (header) field, action field and statistics field. Within an OpenFlow switch, basically the packets have gone through a series of flow tables to find its exact match. For every incoming packet, the switch make the forwarding decision by looking into the flow table entries, starts from the first table and ends either with a match in one of the tables or with a miss if no rule present for the packet. A flow rule can be defined by combining different matching fields,such as port number, source or the destination IPv4 address,source or destination MAC address etc.