How Igmp Works - IBM RackSwitch G8000 Application Manual

How IGMP Works

216
RackSwitch G8000: Application Guide
• Membership Query: Message sent by the Querier to verify if hosts are listening to
a group.
• General Query: A Membership Query sent to all hosts. The Group address field
for general queries is 0.0.0.0 and the destination address is 224.0.0.1.
• Group-specific Query: A Membership Query sent to all hosts in a multicast group.
When IGMP is not configured, switches forward multicast traffic through all ports,
increasing network load. When IGMPv2 is configured on a switch, multicast traffic
flows as follows:
• A server sends multicast traffic to a multicast group.
• The Mrouter sends Membership Queries to the switch, which forwards them to all
ports in a given VLAN.
• Hosts respond with Membership Reports if they want to join a group. The switch
forwards these reports to the Mrouter.
• The switch forwards multicast traffic only to hosts that have joined a group.
• The Mrouter periodically sends Membership Queries to ensure that a host wants
to continue receiving multicast traffic. If a host does not respond, the IGMP
Snooper stops sending traffic to the host.
• The host can initiate the Leave process by sending a Leave Report to the IGMP
Snooper.
• A host can also send a group-specific IGMPv2 Leave message. The IGMP
Snooper queries to find out if any other host connected to the interface is
interested in receiving the multicast traffic. If it does not receive a Join message
in response, the IGMP Snooper removes the group entry and passes on the
information to the Mrouter.
The G8000 supports the following:
• IGMP version 1 and 2
• IGMP version 3 in stand-alone (non-stacking) mode only
• 128 Mrouters
Note: Unknown multicast traffic is sent to all ports if the flood option is enabled and
no Membership Report was learned for that specific IGMP group. If the flood
option is disabled, unknown multicast traffic is discarded if no hosts or
Mrouters are learned on a switch.
To enable or disable IGMP flood, use the following command:
RS G8000(config)
RS G8000(config-vlan)
# vlan <vlan ID>
# [no] flood