The router architecture of each Juniper Networks M-series router and T-series platform cleanly separates routing and control functions from packet forwarding operations, thereby eliminating bottlenecks and permitting the router to maintain a high level of performance. Each router consists of two major architectural components:
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.
Figure 1 illustrates the relationship between the Routing Engine and the Packet Forwarding Engine.
Figure 1: Router Architecture
The Routing Engine consists of an Intel-based PCI platform running JUNOS software. For more information about JUNOS software, see Cheat Sheet for the CLI Commands .A link to the topic “Command Line Interface Overview” should be included here once the topic is created.
The Routing Engine constructs and maintains one or more routing tables. From the routing tables, the Routing Engine derives a table of active routes, called the forwarding table, which is then copied into the Packet Forwarding Engine.
The design of the Internet Processor II and T-series Internet Processor ASICs allows the forwarding table in the Packet Forwarding Engine to be updated without interrupting forwarding performance (see Figure 2).
Figure 2: Routing and Forwarding Table Updates
The Packet Forwarding Engine uses ASICs to perform Layer 2 and Layer 3 packet switching, route lookups, and packet forwarding. On M-series routers, the Packet Forwarding Engine includes the router midplane (on an M40 router, the backplane), Flexible PIC Concentrators (FPCs), Physical Interface Cards (PICs), and other components, unique to each router, that handle forwarding decisions.
The T-series platforms feature multiple Packet Forwarding Engines, up to a maximum of 16 for the T640 Internet routing node and 8 for the T320 Internet router. Each FPC has one or two Packet Forwarding Engines, each with its own memory buffer. Each Packet Forwarding Engine maintains a high-speed link to the Routing Engine. For information about T-series platforms, see the T640 Internet Routing Node Hardware Guide and the T320 Internet Router Hardware Guide.