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Software Configuration Guide—Release 15.0(2)SG
OL-23818-01
Chapter 33 Configuring IP Multicast
About IP Multicast
Figure 33-4 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.
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.
Note For RET, a maximum of 102 K entries is supported (32 K used for floodsets, 70 K used for multicast
entries).
Note Partial routing is not supported on Catalyst 4900M, Catalyst 4948E, Supervisor Engine 6-E, and
Supervisor Engine 6L-E; only hardware and software routing are supported.
68135
Integrated Switching Engine 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 Routing
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