router ports are added to the forwarding table for every Layer 2 multicast
entry. The switch learns of the ports through one of these methods:
Snooping on IGMP
queries, Protocol-Independent Multicast (PIM) packets, and Distance Vector
Multicast Routing Protocol (DVMRP) packets.
- Listening to Cisco Group
Management Protocol (CGMP) packets from other routers.
connecting to a multicast router port using the
ip igmp snooping
mrouter global configuration command.
Static connection using the
ip igmp snooping mrouter command is
supported only for known multicast groups.
You can configure
the switch either to snoop on IGMP queries and PIM/DVMRP packets or to listen
to CGMP self-join or proxy-join packets. By default, the switch snoops on
PIM/DVMRP packets on all VLANs. To learn of multicast router ports through only
CGMP packets, use the ip igmp snooping vlan
vlan-id mrouter learn cgmp global configuration command. When
this command is entered, the router listens to only CGMP self-join and CGMP
proxy-join packets and to no other CGMP packets. To learn of multicast router
ports through only PIM-DVMRP packets, use the ip igmp snooping vlan vlan-id mrouter learn
pim-dvmrp global configuration command.
If you want to use
CGMP as the learning method and no multicast routers in the VLAN are CGMP
proxy-enabled, you must enter the ip cgmp
router-only command to dynamically access the router.