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Multi-level flow table and pipeline processing
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| bet | 3/3 | | Sana | 29.02.2024 | | Hajmi | 94.65 Kb. | | #164416 |
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OpenFlow v1.0 uses a single flow table to match packets. This implementation is simple, but the flow table becomes quite large as various policies are configured to implement increasingly complex network requirements. This makes management of the control plane more difficult, and poses higher requirements on hardware.
OpenFlow v1.1 and later versions support multi-level flow tables and pipeline processing. When a packet arrives at a switch, matching starts from the flow table with the smallest sequence number, and may continue to additional flow tables in the pipeline. Multi-level flow tables can not only implement complex processing on data packets, but also reduce the length of a single flow table and therefore improve the entry lookup efficiency.
Multi-level flow table processing
Flow table delivery
OpenFlow flow tables can be delivered in proactive or reactive mode.
In proactive mode, the controller delivers the flow table information to OpenFlow switches.
In reactive mode, when an OpenFlow switch does not find any flow entry matching a received packet, it sends a message to the controller. The controller then determines how to forward the packet, and calculates and delivers the corresponding flow entry to the switch. In this mode, the switch does not need to maintain all flow entries. Instead, it obtains flow entries from the controller and saves them only for actually generated traffic, and deletes flow entries when they are aged out. Therefore, this mode greatly reduces the occupied chip space on the switch.
Application Scenarios of OpenFlow
With the development and popularization of OpenFlow, its research and application fields are also continuously expanded, covering network virtualization, security and access control, and load balancing. The following describes the typical application scenarios of OpenFlow:
The network of scientific research institutions is where OpenFlow comes into being and also the network environment where OpenFlow is widely used. Students or researchers may need to verify newly designed network control protocols and data forwarding technologies when conducting innovative research on networks. In such cases, they want a platform separating the control plane from the forwarding plane, so that they can flexibly verify their research work. An OpenFlow-based network is such a platform meeting these requirements by providing almost the same complex environment as an actual network, while ensuring a good experiment effect and reducing experiment costs.
Application of OpenFlow on a data center network
OpenFlow starts its large-scale application on cloud data center networks. Deployment of cloud data centers poses many virtualization requirements, such as dynamic creation of multi-tenant resources, traffic isolation, and dynamic migration of virtual machines (VMs). OpenFlow switches can work with the cloud management platform to implement dynamic allocation of network resources and on-demand transmission of network traffic, meeting network virtualization requirements of cloud services and improving network performance. As data centers have heavy traffic, data congestion may occur if transmission paths are not properly allocated, thereby hindering the operational efficiency of data centers. To avoid this situation, OpenFlow can be deployed in data centers to dynamically obtain traffic transmission information of each link and deliver OpenFlow flow entries to load balance traffic among links.
Application of OpenFlow on an enterprise campus network
OpenFlow can be used on a campus network to effectively manage and control access devices, which are large in number, have a relatively high failure rate, but provide simple functions and traffic policies. With OpenFlow, a controller can be deployed to centrally deliver flow entries to access devices, and monitor and manage these devices. In scenarios where user identity authentication is required, the authentication traffic can be diverted to the controller. After user identities are successfully authenticated, the controller delivers admission rules to the switch interfaces connected to users. If the controller detects that a network interface or traffic of a user is abnormal, it delivers rules to disable the interface or control the traffic to quickly rectify network faults, thereby improving network reliability and security.
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