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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 36 Configuring Cisco Express Forwarding
Catalyst 4500 Series Switch Implementation of CEF
Figure 36-2
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) tunnels.
Hardware Switching
•
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.
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:
•
Packets that use IP header options
Note
Packets that use TCP header options are switched in hardware because they do not affect the
forwarding decision.
•
Packets that have an expiring IP time-to-live (TTL) counter
•
Packets that are forwarded to a tunnel interface.
Note
When GRE tunnels are configured without tunnel options, packets are hardware-switched.
•
Packets that arrive with non-supported encapsulation types
•
Packets that are routed to an interface with non-supported encapsulation types
Integrated Switching Engine
CPU Subsystem
GRE
tunnel
L3 physical
interface
Router
L3 interfaces
L2 switchports
68127
VLAN1
Gig 1/1
VLAN2
GRE
tunnel
Содержание Catalyst 4500 Series
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