Hardware Switching - Cisco Catalyst 4500 Series Software Configuration Manual

Chapter 36 Configuring Cisco Express Forwarding
Figure 36-2
The Integrated Switching Engine performs inter-VLAN routing in hardware. The CPU subsystem
software supports Layer 3 interfaces to VLANs that use Subnetwork Access Protocol (SNAP)
encapsulation. The CPU subsystem software also supports generic routing encapsulation (GRE) tunnels.

Hardware Switching

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Software Switching
Software switching occurs when traffic cannot be processed in hardware. The following types of
exception packets are processed in software at a much slower rate:
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Hardware and Software Switching Components
Integrated Switching Engine
L3 physical
interface
Gig 1/1
L3 interfaces
VLAN1
L2 switchports
Hardware switching is the normal operation for switches with supervisor engines.
Beginning in Cisco IOS XE Release 3.7.1E, GRE tunnels are supported on the hardware on
Catalyst 4500 series switches. When GRE is configured without tunnel options, packets are
hardware-switched. Otherwise, packets are switched in the software.
Packets that use IP header options
Packets that use TCP header options are switched in hardware because they do not affect the
Note
forwarding decision.
Packets that have an expiring IP time-to-live (TTL) counter
Packets that are forwarded to a tunnel interface.
When GRE tunnels are configured without tunnel options, packets are hardware-switched.
Note
Packets that arrive with non-supported encapsulation types
Packets that are routed to an interface with non-supported encapsulation types
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Router
GRE
VLAN2
tunnel
Catalyst 4500 Series Switch Implementation of CEF
CPU Subsystem
GRE
tunnel
36-5