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Video – Software-Defined Networking
Click Play to view a video on network programming, software-defined networking (SDN), and controllers.
Control Plane and Data Plane
The previous topic explained virtual network infrastructure. This topic will cover Software- Defined Networking (SDN). SDN was explained in the previous video. We will cover more details here.
A network device contains the following planes:
- Control plane – This is typically regarded as the brains of a device. It is used to make forwarding decisions. The control plane contains Layer 2 and Layer 3 route forwarding mechanisms, such as routing protocol neighbor tables and topology tables, IPv4 and IPv6 routing tables, STP, and the ARP table. Information sent to the control plane is processed by the CPU.
- Data plane – Also called the forwarding plane, this plane is typically the switch fabric connecting the various network ports on a device. The data plane of each device is used to forward traffic flows. Routers and switches use information from the control plane to forward incoming traffic out the appropriate egress interface. Information in the data plane is typically processed by a special data plane processor without the CPU getting involved.
The figure illustrates how Cisco Express Forwarding (CEF) uses the control plane and data plane to process packets.
CEF is an advanced, Layer 3 IP switching technology that enables forwarding of packets to occur at the data plane without consulting the control plane. In CEF, the control plane’s routing table pre-populates the CEF Forwarding Information Base (FIB) table in the data plane. The control plane’s ARP table pre-populates the adjacency table. Packets are then forwarded directly by the data plane based on the information contained in the FIB and adjacency table, without needing to consult the information in the control plane.
SDN is basically the separation of the control plane and data plane. The control plane function is removed from each device and is performed by a centralized controller, as shown in the figure. The centralized controller communicates control plane functions to each device. Each device can now focus on forwarding data while the centralized controller manages data flow, increases security, and provides other services.
Not shown in the figures is the management plane, which is responsible for managing a device through its connection to the network. Network administrators use applications such as Secure Shell (SSH), Trivial File Transfer Protocol (TFTP), Secure FTP, and Secure Hypertext Transfer Protocol (HTTPS) to access the management plane and configure a device. The management plane is how you have accessed and configured devices in your networking studies. In addition, protocols like Simple Network Management Protocol (SNMP), use the management plane.
Network Virtualization Technologies
Over a decade ago, VMware developed a virtualizing technology that enabled a host OS to support one or more client OSs. Most virtualization technologies are now based on this technology. The transformation of dedicated servers to virtualized servers has been embraced and is rapidly being implemented in data center and enterprise networks.
Two major network architectures have been developed to support network virtualization:
- Software-Defined Networking (SDN) – A network architecture that virtualizes the network, offering a new approach to network administration and management that seeks to simplify and streamline the administration process.
- Cisco Application Centric Infrastructure (ACI) – A purpose-built hardware solution for integrating cloud computing and data center management.
Components of SDN may include the following:
- OpenFlow – This approach was developed at Stanford University to manage traffic between routers, switches, wireless access points, and a controller. The OpenFlow protocol is a basic element in building SDN solutions. Search for OpenFlow and the Open Networking Foundation for more information.
- OpenStack – This approach is a virtualization and orchestration platform designed to build scalable cloud environments and provide an IaaS solution. OpenStack is often used with Cisco ACI. Orchestration in networking is the process of automating the provisioning of network components such as servers, storage, switches, routers, and applications. Search for OpenStack for more information.
- Other components – Other components include Interface to the Routing System (I2RS), Transparent Interconnection of Lots of Links (TRILL), Cisco FabricPath (FP), and IEEE 802.1aq Shortest Path Bridging (SPB).
Traditional and SDN Architectures
In a traditional router or switch architecture, the control plane and data plane functions occur in the same device. Routing decisions and packet forwarding are the responsibility of the device operating system. In SDN, management of the control plane is moved to a centralized SDN controller. The figure compares traditional and SDN architectures.
The SDN controller is a logical entity that enables network administrators to manage and dictate how the data plane of switches and routers should handle network traffic. It orchestrates, mediates, and facilitates communication between applications and network elements.
The complete SDN framework is shown in the figure. Note the use of Application Programming Interfaces (APIs) within the SDN framework. An API is a set of standardized requests that define the proper way for an application to request services from another application. The SDN controller uses northbound APIs to communicate with the upstream applications. These APIs help network administrators shape traffic and deploy services. The SDN controller also uses southbound APIs to define the behavior of the data planes on downstream switches and routers. OpenFlow is the original and widely implemented southbound API.
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