Internet Router Hardware Guide

Chapter 4
System Architecture Overview
The router architecture consists of two major components:
Packet Forwarding Engine—Performs Layer 2 and Layer 3 packet switching,
route lookups, and packet forwarding.
Routing Engine—Provides Layer 3 routing services and network management.
The Packet Forwarding Engine and the Routing Engine perform independently but
communicate constantly through a 100-Mbps internal link. This arrangement
provides streamlined forwarding and routing control and the ability to run
Internet-scale networks at high speeds. Figure 22 illustrates the relationship
between the Packet Forwarding Engine and the Routing Engine.
Figure 22: System Architecture
Packet Forwarding
Engine
Routing Engine
1244
Packets
in
Packets
out
100-Mbps link
For a discussion of the architectural components, s ee the following sections:
Packet Forwarding Engine Architecture on page 5 1
RoutingEngineArchitectureonpage53
Packet Forwarding Engine Architecture
The Packet Forwarding Engine performs Layer 2 and Layer 3 packet switching.
It can forward up to 160 for all packet sizes. The aggregate throughput for the
router is 160 gigabits per second (Gbps) simplex or 80 Gbps full duplex. The
Packet Forwarding Engine is implemented in application-specific integrated circuits
(ASICs). It uses a centralized route lookup engine and shared memory.
Packet Forwarding Engine Architecture 51