Ip Multicast Tables - Cisco Catalyst 4500 Series Configuration Manual

Chapter 35 Configuring IP Multicast
on Gig 3/1 sends a multicast packet, the host on Gig 3/2 might also need to receive the packet. To send
a multicast packet to the host on Gig 3/2, all of the switch ports in the ingress VLAN must be added to
the port set that is loaded in the MET.
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 switch ports: (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 switch ports on VLAN 2. The
packet should be forwarded only to switch ports 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 switch ports: (1/1,1/2, 2/1, 2/2, 3/1, and 3/2).

IP Multicast Tables

Figure 35-4
multicast packets in hardware.
Figure 35-4
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-25340-01
shows some key data structures that the Catalyst 4500 series switch uses to forward IP
IP Multicast Tables and Protocols
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 IOS XE 3.3.0SG and IOS 15.1(1)SG
About IP Multicast
CPU Subsystem
Routing Protocols
L3 Protocols
• PIM
• IGMP
L2 Protocols
IGMP
•
snooping
Spanning tree
•
..
..
..
35-7