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NetStructure™ 480T Routing Switch User Guide
The switch also forwards PIM-SM traffic to a PIM-DM network. The
PMBR sends a join message to the RP and the PMBR then broadcasts
traffic from the RP into the PIM-DM network.
There are no new commands that need to be entered to enable PIM-
SM to PIM-DM functionality. By having both the DM mode interface
and SM mode interface on the same router, the PMBR functionality
is automatically enabled.
IP Multicast Cache Display
The show ipmc cache command displays a legend with a summary
of each entry in the table.
IGMP Overview
IGMP is a protocol used by an IP host to register its IP multicast
group membership with a router. The messaging protocol can also be
snooped by a Layer 2 switch, to provide for intelligent forwarding of
multicast data streams within a VLAN.
Periodically, the router queries the multicast group to see if the group
is still in use. If the group is still active, a single IP host responds to
the query, and group registration is maintained.
IGMP is enabled by default on the switch. However, you can
configure the switch to disable the generation of periodic IGMP
query packets. IGMP query should be enabled when the switch is
configured to perform the IP unicast or IP multicast routing.
IGMP Snooping
IGMP snooping is a Layer 2 function that does not require multicast
routing to be enabled. It reduces the flooding of IP multicast traffic.
IGMP snooping optimizes network bandwidth use, and prevents
multicast traffic from flooding to parts of the network that do not need
it. IP multicast traffic is not reduced in the local multicast domain.
IGMP snooping is enabled by default on the 480T routing switch. If
you are using multicast routing, IGMP snooping must be enabled. If