Explain in brief about software defined network? What are its features?

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Software-defined networking (SDN) is an approach via which we take the control plane away from the switch and assign it to a centralized unit called the SDN controller. Hence, a network administrator can shape traffic via a centralized console without having to touch the individual switches. The data plane still resides in the switch and when a packet enters a switch, its forwarding activity is decided based on the entries of flow tables, which are pre-assigned by the controller. A flow table consists of match fields (like input port number and packet header) and instructions. The packet is first matched against the match fields of the flow table entries.

Then the instructions of the corresponding flow entry are executed. The instructions can be forwarding the packet via one or multiple ports, dropping the packet, or adding headers to the packet. If a packet doesn’t find a corresponding match in the flow table, the switch queries the controller which sends a new flow entry to the switch. The switch forwards or drops the packet based on this flow entry.

- Hamro CSIT

A typical SDN architecture consists of three layers.

  • Application layer:
    It contains the typical network applications like intrusion detection, firewall, and load balancing
  • Control layer:
    It consists of the SDN controller which acts as the brain of the network. It also allows hardware abstraction to the applications written on top of it.
  • Infrastructure layer:
    This consists of physical switches which form the data plane and carries out the actual movement of data packets.

Features of SDN:

  1. Agility. As business and applications need to change, administrators can adjust network configuration as required.
  2. Centralized management. SDN consolidates network intelligence, which provides a holistic view of the network configuration and activity.
  3. Programmability. The ability to directly program network features and configure network resources quickly and easily through automated SDN services.
  4. Open connectivity. SDN is based on and implemented via open standards. As a result, SDN streamlines network design and provides consistent networking in a vendor-neutral architecture.
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