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128 Dell Converged Enhanced Ethernet Administrator’s Guide
53-1002116-01
Configuring IGMP
15
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.
Use the following procedure to configure IGMP on a CEE/FCoE switch.
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. Configure a VLAN port member to be a multi-router interface.
switch (config)#interface vlan 25
switch (conf-if-vl-25)#ip igmp snooping mrouter interface intengigabitethernet
0/1
4. Repeat step 3 for each port in the VLAN, as needed.
5. Activate the default IGMP querier functionality for the VLAN.
switch(conf-if-vl-25)#ip igmp snooping querier enable vlan 25
6. Optional: Activate the IGMP querier functionality with additional features.
Configuring IGMP snooping querier
If your multicast traffic is not routed because Protocol-Independent Multicast (PIM) and IGMP are
not configured, use the IGMP snooping querier in a VLAN.