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Routing Engine and Packet Forwarding Engine
A Services Router has two primary software processing components:
■ Routing Engine—The Routing Engine provides three main functions:
■ Creates the packet forwarding switch fabric for the Services Router, providing
route lookup, filtering, and switching on incoming data packets, then directing
outbound packets to the appropriate interface for transmission to the
network.
■ Maintains the routing tables used by the router and controls the routing
protocols that run on the router.
■ Provides control and monitoring functions for the router, including controlling
power and monitoring system status.
■ Packet Forwarding Engine—Processes packets; applies filters, routing policies,
and other features; and forwards packets to the next hop along the route to their
final destination.
For information about Routing Engine hardware, see “J2320 and J2350 Routing
Engine Hardware” on page 18 and “J4350 and J6350 Routing Engine
Hardware” on page 31.
Kernel and Microkernel
The Routing Engine kernel provides the underlying infrastructure for all JUNOS
software processes by doing the following:
■ Linking the routing tables maintained by the routing protocol process with the
forwarding table maintained by the Routing Engine
■ Coordinating communication with the Packet Forwarding Engine, primarily by
synchronizing the Packet Forwarding Engine’s forwarding table with the master
forwarding table maintained by the Routing Engine
The microkernel contains device drivers and processes that the Packet Forwarding
Engine uses to govern the flow of packets through the Services Router.
JUNOS Software Processes
The JUNOS software running on the Routing Engine and Packet Forwarding Engine
consists of multiple processes that are responsible for individual Services Router
functions.
The separation of functions provides operational stability, because each process
accesses its own protected memory space. In addition, because each process is a
separate software package, you can selectively upgrade all or part of the JUNOS
software, for added flexibility.
Table 17 on page 41 describes the primary JUNOS software processes.
40 ■ Software Overview
J2320, J2350, J4350, and J6350 Services Router Getting Started Guide