4.2 OpenFlow switch architecture and flow tables
2 min read•august 9, 2024
OpenFlow switches are the backbone of Software-Defined Networking. They use flow tables to make decisions, for complex actions, and meter tables to control packet rates. These components work together to enable flexible network control.
The switch's ports and queues handle packet input/output and basic QoS. Flow tables match packet headers to determine actions, while pipelines process packets through multiple tables. Counters track important stats for monitoring and management.
OpenFlow Switch Components
Core Components of OpenFlow Switches
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Top images from around the web for Core Components of OpenFlow Switches
Software Defined Network (SDN) and OpenFlow Protocol in 5G Network View original
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The introduction to OVS architecture View original
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Software Defined Network (SDN) and OpenFlow Protocol in 5G Network View original
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The introduction to OVS architecture View original
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- OpenFlow switch forms the foundation of Software-Defined Networking (SDN) architectures
- Flow table serves as the primary decision-making component within an OpenFlow switch
- Group table enables more complex forwarding actions by grouping multiple output actions
- Meter table measures and controls the rate of packets through the switch
Physical and Logical Elements of OpenFlow Switches
- Port represents a physical or virtual interface for packet ingress and egress
- Queue attaches to a port and enables basic Quality of Service (QoS) support through packet scheduling
Flow Table Structure
Match Fields and Actions in Flow Tables
- Match fields define packet header information used to identify flows (source IP address, destination MAC address)
- Actions specify how to handle matched packets (forward, drop, modify)
- Pipeline processing determines the sequence of flow table lookups and actions applied to packets
Flow Table Performance Metrics
- Counters track statistics for each flow, table, port, queue, and meter
- Per-flow counters include packet count, byte count, and flow duration
- Per-table counters measure lookup hits and misses
Key Terms to Review (18)
Control plane: The control plane is a fundamental component of network architecture responsible for managing and directing network traffic by controlling the flow of data packets through the network. It separates the decision-making process from the data forwarding process, allowing for more dynamic and efficient network management and enabling features like programmability and automation.
Controller-to-switch communication: Controller-to-switch communication refers to the interaction and data exchange between a centralized control entity, known as the controller, and individual network switches in a Software-Defined Networking (SDN) environment. This communication is essential for enabling the controller to manage and configure the switches' behavior and flow tables effectively, allowing for dynamic network management and efficient resource allocation.
Data Plane: The data plane is the part of a network that carries user data packets from one point to another. It operates on the forwarding of data based on rules set by the control plane, managing how packets are transmitted and processed through the network infrastructure.
Drop action: Drop action refers to a command in networking protocols that instructs a switch to discard packets without further processing or forwarding. In the context of networking, this action is essential for managing traffic flow and ensuring that unwanted or harmful packets do not congest the network. The ability to implement drop actions effectively allows for enhanced control over data handling in network devices like switches.
Flow Entry: A flow entry is a fundamental component of the flow table in an OpenFlow switch, defining how packets should be processed based on specific match criteria. Each entry consists of matching fields, actions to take when a match is found, and counters for monitoring traffic statistics. Flow entries play a crucial role in how switches make forwarding decisions and manage network traffic, directly influencing performance and efficiency.
Flow eviction: Flow eviction is the process of removing specific flow entries from a flow table in a network device, such as an OpenFlow switch, to manage resources and optimize performance. This technique is crucial for maintaining efficiency, especially when dealing with limited memory space for flow entries and dynamic network conditions. Eviction helps in ensuring that the most relevant and active flows are prioritized while less active or obsolete flows are removed.
Flow Installation: Flow installation refers to the process of setting up flow entries in a switch's flow table, which dictate how incoming packets should be processed and forwarded. This process involves specifying match criteria, actions to be taken on matching packets, and the priority of each flow entry. It is a crucial part of Software-Defined Networking, enabling dynamic control over data flows within the network infrastructure.
Flow rule: A flow rule is a set of instructions within a flow table that defines how packets should be treated by an OpenFlow switch based on specified match criteria. It includes parameters such as the match fields, actions to perform on matching packets, and priority levels that determine the order in which rules are applied. This system allows for dynamic and flexible packet forwarding in a software-defined networking environment.
Forwarding action: Forwarding action refers to the specific operation performed by a network device, particularly in the context of an OpenFlow switch, to determine how incoming packets are processed and where they are sent next. This action is primarily based on matching the packets against flow entries in flow tables, which consist of various rules that dictate the handling of different types of traffic. Understanding forwarding actions is crucial because they enable efficient traffic management and play a key role in the overall performance of software-defined networking (SDN) environments.
Group Tables: Group tables are a feature in OpenFlow that allow for the management of groups of actions to be applied to packets. This mechanism enables more complex operations and the ability to execute multiple actions in a single rule, enhancing the flexibility and efficiency of network management. They evolve as part of OpenFlow’s development, contributing to advanced functionalities such as load balancing and traffic engineering.
IEEE 802.1: IEEE 802.1 is a set of standards developed by the Institute of Electrical and Electronics Engineers (IEEE) that pertains to networking technologies and protocols for local area networks (LANs). This standard plays a crucial role in defining network bridging, virtual LANs (VLANs), and network management, which are essential for efficient data flow and network performance in various environments, including software-defined networking. IEEE 802.1 helps manage how devices communicate over a network and ensures that traffic is properly segmented and directed.
Match Field: A match field is a component in the flow tables of OpenFlow switches that specifies criteria used to identify packets or flows for processing. It allows network operators to define rules that dictate how incoming packets are matched against the fields in the flow entries, enabling precise control over packet handling and forwarding decisions. This plays a crucial role in managing traffic and implementing policies in a software-defined networking environment.
Multi-table support: Multi-table support refers to the capability of a network switch, specifically in the context of OpenFlow architecture, to utilize multiple flow tables to manage data packets. This feature enhances the flexibility and efficiency of packet processing by allowing different flow tables to be used for various types of traffic, enabling more complex and precise networking policies. By organizing flows into separate tables, switches can optimize decision-making and reduce the overhead associated with handling network flows.
ONF - Open Networking Foundation: The Open Networking Foundation (ONF) is a non-profit organization dedicated to promoting and advancing software-defined networking (SDN) and its adoption in various networking environments. It aims to drive innovation in network architecture and management through the development of standards and open-source solutions. By fostering collaboration among industry leaders, the ONF plays a vital role in shaping the future of networking technologies, including the architecture of OpenFlow switches and the design of flow tables that optimize network performance.
OpenFlow Protocol: OpenFlow Protocol is a communications protocol that allows the control of network devices, primarily switches and routers, from a centralized controller. This protocol enables Software-Defined Networking (SDN) by separating the data plane (where data is forwarded) from the control plane (where decisions are made), allowing for more flexible network management and dynamic resource allocation.
Packet processing: Packet processing refers to the manipulation and handling of data packets as they traverse a network. It involves various actions, including forwarding, filtering, and modifying packets based on predefined rules, which are critical for efficient data communication. This process is essential in the context of managing flow tables, as it determines how switches interpret and act upon incoming traffic based on their specific configurations.
Remote Procedure Call: A Remote Procedure Call (RPC) is a protocol that allows a program to execute a procedure or function on a remote server as if it were local. This abstraction enables seamless communication between different machines in a network, facilitating operations such as data retrieval and command execution. RPC plays a critical role in distributed systems by enabling various components to communicate over the network, which is essential for functionalities in modern architectures, such as those used in software-defined networking.
Southbound API: A southbound API is an interface that allows communication between the control layer and the data plane in a Software-Defined Networking (SDN) architecture. It acts as a bridge for controllers to interact with network devices, enabling them to manage and configure network behavior dynamically. This interaction is essential for implementing protocols like OpenFlow, which define how flow tables are populated and maintained in switches, thus impacting control plane functionality, network management practices, and controller communications.