Control Plane and Data Plane

A network can keep forwarding traffic while its routing software is temporarily unavailable. In another system, an administration page works while customer requests fail. ‘The system is up’ does not describe which capabilities still work.

The control plane determines and maintains how a system should operate. The data plane performs the work using that state. On a router, the control plane learns routes and builds the information used for forwarding. The data plane uses the installed forwarding entries to send packets toward their destinations. Some architectures distinguish a separate management plane for administrators' configuration and monitoring actions. The same distinction appears in software platforms: provisioning an application and changing its configuration are control operations; serving its users' requests is data-plane work. The two kinds of operation can have different endpoints, permissions, and scaling needs. Separation can limit the effect of failures. Existing traffic may continue while control operations are unavailable, provided the necessary forwarding state remains valid. That is not guaranteed: the planes may share dependencies, and stale state or a required configuration change can eventually interrupt service.