Cisco Systems WSC4500X16SFP IP Multicast Tables

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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter24 Understanding and Conf iguring IP Multicast
Overview of 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 switchpo rts on VLAN 2. The
packet should be forwarded only to switchports where IGMP snooping has d etermined that there is either
a group member or router. For example, if VLAN 1 had IGMP snooping en abled, 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 24-4 shows some key data structures that the Catalyst4500 series switch uses to forward IP
multicast packets in hardware.
Figure24-4 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 t o 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 spac e for a
total of 128,000 routes, which are shared by unicast routes, multicast routes, and multicast fast-drop
entries.
68135
Integrated Switching E ngine CPU Subsystem
Routing Protocols
L3 Protocols
•PIM
•IGMP
L2 Protocols
•
•
IGMP
snooping
Spanning tree
Hardware FIB Table
(S,G), RPF Vlan, MET Index
(*,G), Interfaces, MET Index
Hardware Tables
Hardware MET Table
(Replication)
Index, set of {Vlan, switchport}
Software Tables
Multicast Rou ting
Table
• (S,G), RPF
output interfaces
L2 Forwarding
Table
Vlan, MAC address
S,G rpf interface met index
S1, G1 vlan 3 1219
S2, G2 vlan 7 1241
*, G4 vlan 99 1356
index set of {vlan, switchport}
0..
.. ..
.. ..
1279 {vlan3, Fa 3/1} {vlan5, Fa 3/2}, …
switchports
interface, set of