Cisco Nexus 7000 Series Configuration Manual page 33

Configuring IGMP
Note IGMPv1 and IGMPv2 membership report suppression occurs only on hosts that are connected to the same
port.
In this figure, router A sends the IGMPv3 group-and-source-specific query to the LAN. Hosts 2 and 3 respond
to the query with membership reports that indicate that they want to receive data from the advertised group
and source. This IGMPv3 feature supports SSM. For information about configuring SSM translation to support
SSM for IGMPv1 and IGMPv2 hosts, see Configuring an IGMP SSM Translation.
Figure 10: IGMPv3 Group-and-Source-Specific Query
Note
IGMPv3 hosts do not perform IGMP membership report suppression.
Messages sent by the designated querier have a time-to-live (TTL) value of 1, which means that the messages
are not forwarded by the directly connected routers on the subnet. You can configure the frequency and number
of query messages sent specifically for IGMP startup, and you can configure a short query interval at startup
so that the group state is established as quickly as possible. Although usually unnecessary, you can tune the
query interval used after startup to a value that balances the responsiveness to host group membership messages
and the traffic created on the network.
Caution
Changing the query interval can severely impact multicast forwarding.
When a multicast host leaves a group, a host that runs IGMPv2 or later sends an IGMP leave message. To
check if this host is the last host to leave the group, the software sends an IGMP query message and starts a
timer that you can configure called the last member query response interval. If no reports are received before
the timer expires, the software removes the group state. The router continues to send multicast traffic for a
group until its state is removed.
You can configure a robustness value to compensate for packet loss on a congested network. The robustness
value is used by the IGMP software to determine the number of times to send messages.
Cisco Nexus 7000 Series NX-OS Multicast Routing Configuration Guide
IGMP Basics
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