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S y s t e m A r c h i t e c t u r e
The router has two major architectural components: The Routing
Engine, which provides Layer 3 routing services and network
management; and the Packet Forwarding Engine, which provides
packet switching, route lookups, and packet forwarding. The
Routing Engine and Packet Forwarding Engine operate
independently, but constantly communicate through a 100-Mbps
link, as illustrated in the figure at the right.
P a c k e t F l o w t h r o u g h t h e
P a c k e t F o r w a r d i n g E n g i n e
To ensure efficient packet flow through
the system, data packet forwarding is
handled by ASICs on the hardware
components. The figure at the right
shows the sequence of packet flow
through the Packet Forwarding Engine.
R o u t i n g E n g i n e A r c h i t e c t u r e
The Routing Engine handles all the routing protocol
processes as well as processes controlling
interfaces, router components, system
management, and user access. These processes run
on top of a kernel that interacts with the Packet
Forwarding Engine.
C o n t r o l P a c k e t H a n d l i n g
The Routing Engine constructs and maintains routing
tables, and derives a table of active routes, called the
forwarding table, from the routing tables. The forwarding
table is then copied into the Packet Forwarding Engine.
M5 and M10 Internet Backbone Routers
PIC
Packet
Controller
in
PIC
Packet
Controller
out
= ASIC
management
JUNOS
processes
software
Forwarding table
updates
Packets
in
Routing Engine
100-Mbps link
Packets
Packet Forwarding
in
Engine
Midplane
FEB
Distributed
Buffer
Manager
I/O
Manager
Distributed
Buffer
Manager
System
Routing
Control
protocols
functions
Kernel
Intel-based PCI platform
Routing protocol
process
Routing Engine
Forwarding table
Packet Forwarding
Engine
Packets
out
Routing
Engine
Internet
Processor
II
System processes
Operating system
Routing protocol
packets from network
Packets
out
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