Chapter 4

System Architecture Overview
The router architectureconsists of two major components:
Packet Forwarding Engine—Performs Layer2 and Layer 3 packet switching,
route lookups, and packet forwarding.
Routing Engine—Provides Layer 3 routing services and network mana gement.
The PacketForwarding Engine and the Routing Engine perform independently but
communicate constantly through a 100-Mbpsinternal link. This arrangement
provides streamlined forwarding and routing control and th e ability to run
Internet-scale networks at highspeeds. Figure 22 illustrates the relationship
between the PacketForwarding Engine and the Routing Engine.
Figure 22: System Architecture
Packet Forwarding
Engine
Routing Engine
1244
Packets
in
Packets
out
100-Mbps link
For a discussionof the architectural components, see the following sections:
Packet Forwarding Engine Architecture on page 51
RoutingEngineArchitectureonpage53

Packet Forwarding Engine Architecture

The Packet Forwarding Engine performs Layer 2 and Layer3 packet switching.
It can forward upto 160 for all packet sizes. The aggregate throughput for the
router is 160 gigabits per second (Gbps) sim plexo r 80 Gbps full duplex. The
Packet Forwarding Engine is implemented in application-specif ic integrated circuits
(ASICs). It uses a centralized route lookup engine and shared memory.
Packet Forwarding Engine Architecture 51