Control and Forwarding Planes in Separate Chassis
The physical separation of the control plane from the forwarding plane in separate chassis is an extension of the existing Juniper Networks router architecture, which separates routing and control functions from packet forwarding operations. The separation of functionality within a router chassis eliminates bottlenecks and permits the router to maintain a high level of performance.
The control plane refers to the capabilities of the Routing Engine. The creation of routing and forwarding tables, maintenance of adjacencies, filtering, policies, and system monitoring are handled by the control plane. In contrast, the forwarding plane of the router consists of the interfaces, the Packet Forwarding Engines, and the switch fabric. See Figure 1.
Figure 1: Router Architecture
The Routing Engine constructs and maintains one or more routing tables and derives a table of active routes, called the forwarding table, that is copied to the Packet Forwarding Engine.
The Packet Forwarding Engine uses ASICs to perform Layer 2 and Layer 3 packet switching, route lookups, and packet forwarding. For T-series routers, the Packet Forwarding Engine is implemented in ASICs that are physically located on the Flexible PIC Concentrator (FPCs) and Physical Interface Card (PICs). The Packet Forwarding Engine receives incoming packets from the PICs installed on the FPC and forwards them through the switch planes to the appropriate destination port.
The Routing Engine and Packet Forwarding Engine perform their primary tasks independently, while constantly communicating through a high-speed internal link. This arrangement provides streamlined forwarding and routing control and the capability to run Internet-scale networks at high speeds.
With Routing Engines located in a separate chassis, the JCS 1200 platform provides a greatly expanded control plane capacity without sacrificing any forwarding slots in the T-series routing platform. All memory-intensive processing occurs on the Routing Engines, whereas the FPCs on the T-series routing platform are dedicated to efficient high-speed forwarding.