Core features of SDN

Regardless of an open source or a proprietary SDN platform, there are core features and capabilities that require the SDN platform to support. These capabilities include:

• Fabric programmability: Providing the ability to redirect traffic, apply filters to packets (dynamically), and leverage templates to streamline the creation of custom applications. Ensuring northbound APIs allows the control information centralized in the controller available to be changed by SDN applications. This will ensure that the controller can dynamically adjust the underlying network to optimize traffic flows to use the least expensive path, take into consideration varying bandwidth constraints, and meet the quality of service (QoS) requirements.
• Southbound protocol support: Enabling the controller to communicate to switches and routers and manipulate and optimize how they manage the flow of traffic. Currently OpenFlow is the most standard protocol used between different networking vendors, while there are other southbound protocols that can be used. An SDN platform should support different versions of OpenFlow in order to provide compatibility with different switching equipments.
• External API support: Ensuring the controller can be used within the varied orchestration and cloud environments such as VMware vSphere, OpenStack, and so on. By using APIs the orchestration platform can communicate with the SDN platform in order to publish network policies. For example, VMware vSphere shall talk to the SDN platform to extend the virtual distributed switches (vDS) from virtual environment to the physical underlay network without any requirement from an network engineer to configure the network.
• Centralized monitoring and visualization: Since the SDN controller has a full visibility over the network, it can offer end-to-end visibility of the network and centralized management to improve overall performance, simplify the identification of issues, and accelerate troubleshooting. The SDN controller will be able to discover and present a logical abstraction of all the physical links in the network, also it can discover and present a map of connected devices (MAC addresses), which are related to virtual or physical devices connected to the network. The SDN controller support monitoring protocols, such as syslog, snmp, and APIs in order to integrate with third-party management and monitoring systems.
• Performance: Performance in an SDN environment mainly depends on how fast the SDN controller fills the flow tables of SDN enabled switches. Most SDN controllers pre-populate the flow tables on switches to minimize the delay. When an SDN enabled switch receives a packet that doesn't find a matching entry in its flow table, it sends the packet to the SDN controller in order to find where the packet needs to get forwarded to. A robust SDN solution should ensure that the number of requests from switches are minimum and the SDN controller doesn't become a bottleneck in the network.
• High availability and scalability: Controllers must support high availability clusters to ensure reliability and service continuity in case of failure of a controller. Clustering in the SDN controller expands to scalability. A modern SDN platform should support scalability in order to add more controller nodes with load balancing in order to increase the performance and availability. Modern SDN controllers support clustering across multiple different geographical locations.
• Security: Since all switches communicate with SDN controller, the communication channel needs to be secured to ensure unauthorized devices doesn't compromise the network. SDN controller should secure the southbound channels, use encrypted messaging, and mutual authentication to provide access control. Apart from that the SDN controller must implement preventive mechanisms to prevent from denial of services attacks. Also deployment of authorization levels and level controls for multi-tenant SDN platforms is a key requirement.

Apart from the aforementioned features SDN controllers are likely to expand their function in future. They may become a network operating system and change the way we used to build networks with hardware, switches, SFPs, and gigs of bandwidth. The future will look more software defined, as the silicon and hardware industry has already delivered their promises for high performance networking chips of 40G, 100G. The industry needs more time to digest the new hardware and silicons and refresh the equipment with new gears supporting 10 times the current performance.