Cef, Mfib, And Layer 2 Forwarding - Cisco Catalyst 4500 Series Configuration Manual

Chapter 35 Configuring IP Multicast
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 35-2
hardware.
Figure 35-2
Integrated Switching Engine (ASIC)
L3 physical
interface
Gig 1/1
This section contains the following subsections:
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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
upper-layer routing table, only one route needs to be changed in the hardware routing state. To forward
unicast packets in hardware, the integrated switching engine looks up source and destination routes in
ternary content addressable memory (TCAM), takes the adjacency index from the hardware FIB, and
gets the Layer 2 rewrite information and next-hop address from the hardware adjacency table.
The new Multicast Forwarding Information Base (MFIB) subsystem is the multicast analog of the
unicast CEF. The MFIB subsystem extracts the multicast routes that PIM and IGMP create and refines
them into a protocol-independent format for forwarding in hardware. The MFIB subsystem removes the
OL-25340-01
shows a logical view of Layer 2 and Layer 3 forwarding in the integrated switching engine
Logical View of Layer 2 and Layer 3 Forwarding in Hardware
Logical Router
L3 logical
interfaces
VLAN1
L2 switchports
CEF, MFIB, and Layer 2 Forwarding, page 35-5
IP Multicast Tables, page 35-7
Hardware and Software Forwarding, page 35-8
Non-Reverse Path Forwarding Traffic, page 35-10
Multicast Fast Drop, page 35-10
Multicast Forwarding Information Base, page 35-11
S/M, 224/4, page 35-12
VLAN2
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
About IP Multicast
35-5