Cisco 4500M Software Manual page 321

Chapter 24 Configuring Cisco Express Forwarding
Figure 24-2 Hardware and Software Switching Components
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) tunnel.
Hardware Switching
Hardware switching is the normal operation for the Supervisor Engine III and Supervisor Engine IV.
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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OL-6696-01
Integrated Switching Engine
L3 physical
interface
Gig 1/1
L3 interfaces
VLAN1
L2 switchports
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
Packets that arrive with non-supported encapsulation types
Packets that are routed to an interface with non-supported encapsulation types
Packets that exceed the MTU of an output interface and must be fragmented
Packets that require an IGMP redirect to be routed
802.3 Ethernet packets
Router
VLAN2
tunnel
Software Configuration Guide—Release 12.2(25)EW
Catalyst 4500 Series Switch Implementation of CEF
CPU Subsystem
GRE GRE
tunnel
24-5