Hardware And Software Forwarding - Cisco Catalyst 4500 Series Configuration Manual

About IP Multicast
Output interface lists are stored in the multicast expansion table (MET). The MET has room for up to
32,000 output interface lists. (For RET, we can have up to 102 K entries (32 K used for floodsets, 70,000
used for multicast entries)). The MET resources are shared by both Layer 3 multicast routes and by Layer
2 multicast entries. The actual number of output interface lists available in hardware depends on the
specific configuration. If the total number of multicast routes exceed 32,000, multicast packets might not
be switched by the Integrated Switching Engine. They would be forwarded by the CPU subsystem at
much slower speeds.
For RET, a maximum of 102 K entries is supported (32 K used for floodsets, 70 K used for multicast
Note
entries).
Prior to Release IOS XE 3.3.0SG and IOS 15.1(1)SG, partial routing is not supported on Catalyst
Note
4900M, Catalyst 4948E, Supervisor Engine 6-E, Supervisor Engine 6L-E, Supervisor Engine 7-E, and
Supervisor Engine 7L-E; only hardware and software routing are supported. Starting with Release IOS
XE 3.3.0SG and IOS 15.1(1)SG, partial routing is supported on all supervisor engines.

Hardware and Software Forwarding

The integrated switching engine forwards the majority of packets in hardware at very high rates of speed.
The CPU subsystem forwards exception packets in software. Statistical reports should show that the
integrated switching engine is forwarding the vast majority of packets in hardware.
Figure 35-5
Figure 35-5
In the normal mode of operation, the integrated switching engine performs inter-VLAN routing in
hardware. The CPU subsystem supports generic routing encapsulation (GRE) tunnels for forwarding in
software.
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
35-8
shows a logical view of the hardware and software forwarding components.
Hardware and Software Forwarding Components
Integrated Switching Engine
L3 physical
interface
Gig 1/1
L3 interfaces
VLAN1 VLAN2
L2 switchports
CPU Subsystem
Router
GRE
tunnel
Chapter 35 Configuring IP Multicast
GRE
tunnel
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