Optimal packet forwarding requires a decoupling of the control plane and data plane.
- Control Plane: Largely associated with RAM or memory, aligns with the characteristics of an EIGRP topology table or OSPF database. Signaling and message exchange with routing protocol neighbors happens here. The control plan, via its routing table, informs the packet forwarding decisions made by the data plane.
- Data Plane: The realm of production traffic, this is largely aligned with hardware, which is optimal because it processes traffic much quicker than the CPU/memory. Incoming IP packets are accepted into the router via the data plane, rewritten, and forwarded out their destination interface. The decisions made at this layer are informed by the control plane.
In addition to the management of internal data and control circuits that govern the packet forwarding functions, here are other special considerations for the control plane:
- Some traffic cannot be switched/forwarded in hardware. Packets that are sent to the route processor for forwarding decision are the domain of the control plane.
- Collection of statistics from the data plane is a function of the control plane.
- Extracting control information from L2-L3 bridging data in the packet and notification of the data plane thereof.
Stuck-in-Active: Journal of an IT-Network Administrator 