Cisco 4500M Software Manual page 333

Chapter 25 Understanding and Configuring IP Multicast
If VLAN 1 contains 1/1 and 1/2, VLAN 2 contains 2/1 and 2/2, and VLAN 3 contains 3/1 and 3/2, the
MET chain for this route would contain these switchports: (1/1,1/2,2/1,2/2,3/1, and 3/2).
If IGMP snooping is on, the packet should not be forwarded to all output switchports on VLAN 2. The
packet should be forwarded only to switchports where IGMP snooping has determined that there is either
a group member or router. For example, if VLAN 1 had IGMP snooping enabled, and IGMP snooping
determined that only port 1/2 had a group member on it, then the MET chain would contain these
switchports: (1/1,1/2, 2/1, 2/2, 3/1, and 3/2).
IP Multicast Tables
Figure 25-4
multicast packets in hardware.
Figure 25-4 IP Multicast Tables and Protocols
The Integrated Switching Engine maintains the hardware FIB table to identify individual IP multicast
routes. Each entry consists of a destination group IP address and an optional source IP address. Multicast
traffic flows on primarily two types of routes: (S,G) and (*,G). The (S,G) routes flow from a source to a
group based on the IP address of the multicast source and the IP address of the multicast group
destination. Traffic on a (*,G) route flows from the PIM RP to all receivers of group G. Only
sparse-mode groups use (*,G) routes. The Integrated Switching Engine hardware contains space for a
total of 128,000 routes, which are shared by unicast routes, multicast routes, and multicast fast-drop
entries.
OL-6696-01
shows some key data structures that the Catalyst 4500 series switch uses to forward IP
Integrated Switching Engine
Hardware Tables
Hardware FIB Table
(S,G), RPF Vlan, MET Index
(*,G), Interfaces, MET Index
Hardware MET Table
(Replication)
Index, set of {Vlan, switchport}
S,G rpf interface met index
S1, G1 vlan 3
S2, G2 vlan 7
*, G4 vlan 99
Software Tables
Multicast Routing
Table
• (S,G), RPF
interface, set of
output interfaces
L2 Forwarding
Table
Vlan, MAC address
switchports
index set of {vlan, switchport}
1219 0
1241 ..
..
1279
1356 {vlan3, Fa 3/1} {vlan5, Fa 3/2}, ...
Software Configuration Guide—Release 12.2(25)EW
Overview of IP Multicast
CPU Subsystem
Routing Protocols
L3 Protocols
• PIM
• IGMP
L2 Protocols
IGMP
•
snooping
Spanning tree
•
..
..
..
25-7