Cisco Systems 4500 IP Multicast Implementation on the Catalyst 4500 Series Switch

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Software Configuration Guide—Release 15.0(2)SG
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Chapter 33 Configuring IP Multicast About IP Multicast
IP Multicast Implementation on the Catalyst 4500 Series Switch
The Catalyst 4500 series switch supports an ASIC-based integrated switching engine that provides
Ethernet bridging at Layer 2 and IP routing at Layer 3. Because the ASIC is specifically designed to
forward packets, the integrated switching engine hardware provides very high performance with ACLs
and QoS enabled. At wire-speed, forwarding in hardware is significantly faster than the CPU subsystem
software, which is designed to handle exception packets.
The integrated switching engine hardware supports interfaces for inter-VLAN routing and switch ports
for Layer 2 bridging. It also provides a physical Layer 3 interface that can be configured to connect with
a host, a switch, or a router.
Figure 33-2 shows a logical view of Layer 2 and Layer 3 forwarding in the integrated switching engine
hardware.
Figure 33-2 Logical View of Layer 2 and Layer 3 Forwarding in Hardware
This section contains the following subsections:
• CEF, MFIB, and Layer 2 Forwarding, page 33-5
• IP Multicast Tables, page 33-7
• Hardware and Software Forwarding, page 33-9
• Non-Reverse Path Forwarding Traffic, page 33-10
• Multicast Fast Drop, page 33-11
• Multicast Forwarding Information Base, page 33-12
• S/M, 224/4, page 33-13
CEF, MFIB, and Layer 2 Forwarding
The implementation of IP multicast on the Catalyst 4500 series switch is an extension of centralized
Cisco Express Forwarding (CEF). CEF extracts information from the unicast routing table, which is
created by unicast routing protocols, such as BGP, OSPF, and EIGR and loads it into the hardware
Forwarding Information Base (FIB). With the unicast routes in the FIB, when a route is changed in the
Integrated Switching Engine (ASIC)
L3 physical
interface
Logical Router
L3 logical
interfaces
L2 switchports
68402
VLAN1
Gig 1/1
VLAN2