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9-28
Chapter 9
Cajun P550/P880/P882 Switch User Guide
In addition, IP multicasting distributes information to multicast
groups in two specific ways:
■ Multicast Forwarding - allows a switch to forward
multicast traffic from the local router to group members on
directly attached subnetworks. If a multicast packet is
forwarded to multiple interfaces on one VLAN, only one
Forwarding Entry is added on the VLAN for the packet. One
copy of the packet is sent to the VLAN.
■ Multicast Routing - allows a switch to deliver multicast
traffic between neighboring routers and across the network.
For example, the switch could use Internet Group Management
Protocol (IGMP) only to forward multicast traffic to locally attached
subnetworks. However, if the multicast traffic in question is needed
to be sent to a neighboring router, the switch could use DVMRP to
send the information between routers. Since IGMP is a required
protocol for any multicast routing protocol (for example, DVMRP),
it is automatically enabled when you enable DVMRP.
* Note: You must globally enable IP multicast routing in order to
successfully configure IGMP or DVMRP. Refer to
"Configuring Internet Protocol (IP) Global Routing,"
earlier in this chapter, for instructions on enabling IP
multicast routing.
Configuring IGMP
IGMP enables hosts to inform routers when they join or leave
groups. Routers periodically query hosts (query interval) for the
groups in which the hosts are members. When there is more than
one router in a broadcast domain (subnet), one of the routers
becomes the designated querier. Only the designated router queries
the hosts.
Both IGMP Version 1.0 and IGMP Version 2.0 are supported. After
selecting the specific IGMP version for an interface, you can
manually configure the Version 1.0 querier. The selection of the
querier for Version 2.0 is dynamic but can be overridden.
Configuring IGMP includes enabling IGMP and the MTRACE
globally on the switch. You can do this from either the web agent or
the CLI.