Internet Router Hardware Guide

System Architecture Overview
JUNOS Internet software can efficiently support large numbers of interfaces
and virtual circ uits.
Management interface—Different levels of system management tools are
provided, including the JUNOS command-line interface (CLI), the JUNOScript
application programming interface, the craft interface, and S NMP.
Storage and change management—Configuration files, system images, and
microcode can be held and maintained in primary and secondary storage
systems, permitting local or remote upgrades.
Monitoring efficiency and flexibility—The router supports functions such
as alarm handling and packet counting on every port, without degrading
packet-forwarding performance.
The Routing Engine constructs and maintains one or more routing tables (see
Figure 25). 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 ASICs allow the forwarding table in the Packet Forwarding
Engine to be updated without interrupting forwarding performance .
Figure 25: Control Packet Handling for Routing and Forwarding Table Updates
Packets
in
Packets
out
Packet Forwarding
Engines
Forwarding table
Forwarding table
updates
Routing protocol
packets from network
Routing Engine
Routing protocol
process
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Routing Engine Architecture 55