Service Function Chaining (SFC) is a crucial network architecture concept that enables the dynamic steering of traffic through a sequence of network services. In environments like OpenStack Networking, SFC is implemented using ports, allowing for a flexible and programmable way to manage network traffic flow and apply various service functions. By creating port chains, network administrators can define specific paths for traffic to traverse, ensuring it passes through necessary service functions in a defined order.
A port chain, also known as a service function path, is essentially a defined route for network traffic. It is composed of two key elements:
- A Sequence of Ports: These ports represent the service functions themselves and dictate the order in which traffic is processed. When a service function requires two ports, the first acts as the ingress port, receiving traffic, and the second as the egress port, sending traffic after processing. In some cases, a single port can function as both ingress and egress for a bidirectional service.
- Flow Classifiers: These are rules that identify specific traffic flows that need to be directed through the port chain. A flow classifier ensures that only the intended traffic is subjected to the service function chain, maintaining network efficiency and control. Each flow classifier is uniquely associated with a single port chain to avoid conflicts in traffic handling. However, multiple flow classifiers can be linked to the same port chain if different traffic flows require the same service path.
Service function chaining, as implemented with port chains, is inherently unidirectional. This means a port chain defines traffic flow in one direction. To establish bidirectional service function chaining, two unidirectional port chains are required, one for each direction of traffic flow.
Currently, the service function chaining framework within OpenStack Networking primarily supports service functions within a single project. Looking ahead, the architecture is designed to be adaptable and supports various backend service providers through plug-ins. These include drivers like the OVS (Open vSwitch) driver and compatibility with different SDN (Software-Defined Networking) controller drivers. This driver API provides a common interface, allowing different vendors and technologies to implement the actual rendering of the service chain paths.
For more in-depth technical information, refer to the developer documentation.
