SDN – Basics

Getting Started:
The key idea of an SDN is to split the network forwarding function, performed by the data plane, from the network control function, performed by the control plane. This allows a simpler and more flexible network control and management, and also network virtualization. 
OpenFlow is the main SDN implementation.
The network controller communicates with OpenFlow switches using the OpenFlow protocol through a secure channel. Using this connection, the controller is able to configure the forwarding tables of the switch.
If the devices do not have a rule for the data packet that has arrived, the devices forward the packet to the controller for review. The controller determines what to do with the packet and, if necessary, sends a new rule to the device so that it can handle future data packets in the same manner.
The control plane generates the routing table, whereas the data plane, using the control plane tables, determines where the packets should be sent to.
Interesting, yeah?


SDN allows for virtualization of networks so that one can look at the network more abstractly and focus on the big picture rather than on all the gritty details.
Example being Vmware NSX.

In much the same way that server virtualization programmatically creates, snapshots, deletes and restores software-based virtual machines (VMs), VMware NSX network virtualization programmatically creates, snapshots, deletes, and restores software-based virtual networks. 
With network virtualization, the functional equivalent of a “network hypervisor” reproduces the complete set of layer 2 to layer 7 networking services (e.g., switching, routing, firewallingand load balancing) in software. As a result, these services can be programmatically assembled in any arbitrary combination, to produce unique, isolated virtual networks in a matter of seconds.
SDN Based Current Projects being worked on:
Currently, there are several projects that use OpenFlow, which includes Europe and Brazil. In Europe, eight islands are currently interconnected using OpenFlow, whereas in Brazil, there are plans to create a network that will work with that in Europe to create a more widespread testbed. The project in Brazil is particularly important because replacing the Internet is a global endeavor, and a network that will only work with landmasses clustered together is not a viable solution
Future capabilities of SDN:

Updating the Internet brings many challenges because it is constantly being used; it is difficult to test new ideas and strategies to solve the problems found in an existing network. SDN technologies provide a means of testing ideas for a future Internet without changing the current network
Rural areas will also benefit from SDN based solutions.
SDN allows companies to decrease startup costs in rural environments, thereby allowing them to gain more profit. As rural networks become more profitable, more companies will be willing to give access to more and more rural areas.
Another benefit seen is moving the workload to underused networks. If a network is busy at a certain time of the day, the workload might be completed sooner in a network of a different time zone or in a network that is more energy efficient.

Network Innovation through Openflow and SDN -Fei Hu


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