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23-4
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter23 Configuring Cisco Express Forwarding
Catalyst 4500 Series Switch Implementation of CEF
Figure 23-1 Logical L2/L3 Switch Components
The Integrated Switching Engine performs inter-VLAN routing on logical Layer 3 interfaces with the
ASIC hardware. The ASIC hardware also supports a physical Layer 3 interface that can be configured
to connect with a host, a switch, or a router.
Hardware and Software Switching
For the majority of packets, the Integrated Switching Engine performs the packet forwarding function in
hardware. These packets are hardware-switched at very high rates. Exception packets are forwarded by
the CPU subsystem software. Statistic reports should show that the Integrated Switching Engine is
forwarding the vast majority of packets in hardware. Software forwarding is significantly slower than
hardware forwarding, but packets forwarded by the CPU subsystem do not reduce hardware forwarding
speed.
Figure 23-2 shows a logical view of the Integrated Switching Engine and the CPU subsystem switching
components.
Integrated Switching Engine (ASIC)
L3 physical
interface
Logical Router
L3 logical
interfaces
L2 switchports
68402
VLAN1
Gig 1/1
VLAN2