8.2 Southbound API standards and implementations

Southbound API standards are crucial in SDN, enabling communication between controllers and network devices. OpenFlow, the primary protocol, allows direct manipulation of flow tables. Other standards like NETCONF, BGP-LS, and PCEP provide additional capabilities for configuration, topology discovery, and path computation.

Programmable data planes, enabled by languages like P4, offer flexibility in defining packet processing behaviors. These standards and implementations collectively form a rich ecosystem for SDN, allowing for more dynamic, efficient, and customizable network management and control.

OpenFlow-based Protocols

OpenFlow and Its Components

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• Southbound API facilitates communication between SDN controller and network devices
• OpenFlow serves as a primary protocol for SDN southbound interfaces
  • Enables direct access to forwarding plane of network devices
  • Allows manipulation of flow tables on switches and routers
• OpenFlow protocol consists of three main components:
  • Flow table defines packet handling rules
  • Secure channel connects switches to controller
  • OpenFlow protocol standardizes communication between switches and controller
• OVSDB (Open vSwitch Database Management Protocol) manages Open vSwitch implementations
  • Complements OpenFlow by handling switch configuration and monitoring
  • Uses JSON-RPC for encoding and transmitting data

OpenFlow Configuration and Management

• OF-Config (OpenFlow Configuration and Management Protocol) extends OpenFlow capabilities
  • Provides a standard way to configure OpenFlow-enabled switches
  • Manages multiple OpenFlow datapaths on a single physical switch
• OF-Config uses NETCONF as its transport protocol
  • Enables remote configuration of OpenFlow switches
  • Supports operations like creating, modifying, and deleting OpenFlow resources
• OpenFlow protocol versions have evolved over time
  • Version 1.0 introduced basic flow matching and actions
  • Later versions (1.3, 1.4, 1.5) added features like group tables and metering

Network Configuration Protocols

NETCONF and Its Features

• NETCONF (Network Configuration Protocol) provides mechanisms to install, manipulate, and delete network device configurations
  • Uses XML-based data encoding for configuration data and protocol messages
  • Operates over secure transport protocols (SSH, TLS)
• NETCONF key features include:
  • Distinction between configuration and state data
  • Support for multiple configuration datastores (running, candidate, startup)
  • Transactional changes across multiple devices
  • Rollback capability for configuration changes
• NETCONF operations include:
  • get, get-config for retrieving data
  • edit-config for modifying configurations
  • copy-config, delete-config for managing configuration datastores

Traditional Network Management Protocols

• CLI (Command Line Interface) remains a widely used method for device configuration
  • Provides direct access to network devices through text-based commands
  • Varies between vendors, lacking standardization
  • Automation challenges due to inconsistent output formats
• SNMP (Simple Network Management Protocol) focuses on network monitoring and management
  • Uses a manager-agent model for communication
  • Operates through GET, SET, and TRAP operations
  • Organized data in MIBs (Management Information Bases)
  • Limited in configuration management capabilities compared to NETCONF

Routing and Path Computation Protocols

BGP-LS for Network Topology Discovery

• BGP-LS (Border Gateway Protocol - Link State) extends BGP to distribute link-state information
  • Enables SDN controllers to obtain a global view of network topology
  • Facilitates traffic engineering and path computation across domains
• BGP-LS key features:
  • Distributes IGP (OSPF, IS-IS) topology information using BGP
  • Supports both IPv4 and IPv6 topologies
  • Includes node, link, and prefix information in its advertisements
• BGP-LS use cases:
  • Centralized path computation for traffic engineering
  • Inter-domain routing optimization
  • Network visualization and monitoring

PCEP for Path Computation and Traffic Engineering

• PCEP (Path Computation Element Protocol) enables communication between PCCs and PCEs
  • PCC (Path Computation Client) requests optimal paths
  • PCE (Path Computation Element) computes paths based on network constraints
• PCEP operations include:
  • Path computation requests and replies
  • Notification of computation errors or events
  • Monitoring of PCE state
• PCEP applications in SDN:
  • Traffic engineering across multiple domains
  • Bandwidth optimization for large-scale networks
  • Dynamic path provisioning for service-aware networking

Programmable Data Plane

P4 Language for Data Plane Programming

• P4 (Programming Protocol-independent Packet Processors) allows programming of packet forwarding behavior
  • Enables definition of custom packet headers and processing logic
  • Supports various targets (switches, NICs, software switches)
• P4 key concepts:
  • Headers define packet structure
  • Parser specifies packet parsing logic
  • Match-action tables define packet processing rules
  • Control flow determines the sequence of operations
• P4 benefits in SDN:
  • Protocol independence allows for rapid innovation
  • Increased flexibility in defining forwarding behavior
  • Improved visibility and control over network functions

ForCES Framework for Flexible Network Device Architecture

• ForCES (Forwarding and Control Element Separation) provides a framework for separating control and forwarding planes
  • Defines a model for control and forwarding elements
  • Specifies protocols for communication between elements
• ForCES components:
  • CE (Control Element) implements control plane functionality
  • FE (Forwarding Element) handles packet forwarding
  • ForCES protocol facilitates CE-FE communication
• ForCES applications:
  • Enables flexible network device architectures
  • Allows for dynamic reconfiguration of forwarding elements
  • Supports virtualization of network functions