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128 Converged Enhanced Ethernet Administrator’s Guide
53-1002163-02
Configuring IGMP
13
DRAFT: BROCADE CONFIDENTIAL
Multicast routing
Multicast routers use IGMP to learn which groups have members on each of their attached physical
networks. A multicast router keeps a list of multicast group memberships for each attached
network, and a timer for each membership.
NOTE
“Multicast group memberships” means that at least one member of a multicast group on a given
attached network is available.
There are two ways that hosts join multicast routing groups:
• Send an unsolicited IGMP join request
• Send an IGMP join request as a response to a general query from a multicast router
In response to the request, the switch creates an entry in its Layer 2 forwarding table for that VLAN.
When other hosts send join requests for the same multicast, the switch adds them to the existing
table entry. Only one entry is created per VLAN in the Layer 2 forwarding table for each multicast
group.
IGMP snooping suppresses all but one of the host join messages per multicast group and forwards
this one join message to the multicast router. The switch forwards multicast traffic for the specified
multicast group to the interfaces where the join messages were received.
Configuring IGMP
By default, IGMP snooping is globally disabled on all VLAN interfaces. Refer to the CEE Command
Reference for complete information about the commands in this section.
To configure IGMP, use the following procedure in privileged EXEC mode.
1. Enter the configure terminal command to access global configuration mode.
2. Enter the ip igmp snooping enable command to enable IGMP for all interfaces.
This command ensures that IGMP snooping is active on all interfaces.
switch(config)#ip igmp snooping enable
3. Enter VLAN interface configuration mode.
switch(config)#interface vlan 25
4. Configure a VLAN port member to be a multi-router interface.
switch(conf-if-vl-25)#ip igmp snooping mrouter interface tengigabitethernet
0/1
5. Repeat step 4 for each port in the VLAN, as needed.
6. Return to global configuration mode.
switch(conf-if-vl-25)#exit
7. Enable snooping fast-leave.
switch(config)#ip igmp snooping fast-leave
8. Activate the default IGMP querier functionality for the VLAN.
switch(conf-if-vl-25)#ip igmp snooping querier enable