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This chapter describes how to configure Internet Group Management Protocol (IGMP) snooping on Cisco NX-OS switches.
This chapter includes the following sections:
Note We recommend that you do not disable IGMP snooping on the switch. If you disable IGMP snooping, you may see reduced multicast performance because of excessive false flooding within the switch.
The Internet Group Management Protocol (IGMP) snooping software examines Layer 2 IP multicast traffic within a VLAN to discover the ports where interested receivers reside. Using the port information, IGMP snooping can reduce bandwidth consumption in a multi-access LAN environment to avoid flooding the entire VLAN. The IGMP snooping feature tracks which ports are attached to multicast-capable routers to help the routers forward IGMP membership reports. The IGMP snooping software responds to topology change notifications. By default, IGMP snooping is enabled on the switch.
Figure 5-1 shows an IGMP snooping switch that sits between the host and the IGMP router. The IGMP snooping switch snoops the IGMP membership reports and Leave messages and forwards them only when necessary to the connected IGMP routers.
Figure 5-1 IGMP Snooping Switch
The IGMP snooping software operates upon IGMPv1, IGMPv2, and IGMPv3 control plane packets where Layer 3 control plane packets are intercepted and influence the Layer 2 forwarding behavior.
For more information about IGMP, see Chapter3, “Configuring IGMP”
The Cisco NX-OS IGMP snooping software has the following proprietary features:
For more information about IGMP snooping, see RFC 4541 .
This section includes the following topics:
Both IGMPv1 and IGMPv2 support membership report suppression, which means that if two hosts on the same subnet want to receive multicast data for the same group, then the host that receives a member report from the other host suppresses sending its report. Membership report suppression occurs for hosts that share a port.
If no more than one host is attached to each VLAN switch port, then you can configure the fast leave feature in IGMPv2. The fast leave feature does not send last member query messages to hosts. As soon as the software receives an IGMP leave message, the software stops forwarding multicast data to that port.
IGMPv1 does not provide an explicit IGMP leave message, so the software must rely on the membership message timeout to indicate that no hosts remain that want to receive multicast data for a particular group.
Note The software ignores the configuration of the last member query interval when you enable the fast leave feature because it does not check for remaining hosts.
The IGMPv3 snooping implementation on Cisco NX-OS supports full IGMPv3 snooping, which provides constrained flooding based on the (S, G) information in the IGMPv3 reports. This source-based filtering enables the switch to constrain multicast traffic to a set of ports based on the source that sends traffic to the multicast group.
By default, the software tracks hosts on each VLAN port. The explicit tracking feature provides a fast leave mechanism. Because every IGMPv3 host sends membership reports, report suppression limits the amount of traffic that the switch sends to other multicast-capable routers. When report suppression is enabled, and no IGMPv1 or IGMPv2 hosts requested the same group, the software provides proxy reporting. The proxy feature builds the group state from membership reports from the downstream hosts and generates membership reports in response to queries from upstream queriers.
Even though the IGMPv3 membership reports provide a full accounting of group members on a LAN segment, when the last host leaves, the software sends a membership query. You can configure the parameter last member query interval. If no host responds before the timeout, the software removes the group state.
When PIM is not enabled on an interface because the multicast traffic does not need to be routed, you must configure an IGMP snooping querier to send membership queries. You define the querier in a VLAN that contains multicast sources and receivers but no other active querier.
When an IGMP snooping querier is enabled, it sends out periodic IGMP queries that trigger IGMP report messages from hosts that want to receive IP multicast traffic. IGMP snooping listens to these IGMP reports to establish appropriate forwarding.
IGMP filtering allows users to configure a router port on the switch that leads the switch to a Layer 3 multicast switch. The switch stores all manually configured static router ports in its router port list.
When an IGMP packet is received, the switch forwards the traffic through the router port in the VLAN. The switch recognizes a port as a router port through the PIM hello message or the IGMP query received by the switch.
You can define multiple virtual routing and forwarding (VRF) instances. An IGMP process supports all VRFs.
You can use the show commands with a VRF argument to provide a context for the information displayed. The default VRF is used if no VRF argument is supplied.
For information about configuring VRFs, see the Cisco Nexus 3548 Switch NX-OS Unicast Routing Configuration Guide.
The following table shows the licensing requirements for this feature:
Table 5-1 lists the default settings for IGMP snooping parameters.
To affect the operation of the IGMP snooping process, you can configure the optional IGMP snooping parameters described in Table 5-2 .
4.
ip igmp snooping
ip igmp snooping explicit-tracking
ip igmp snooping fast-leave
ip igmp snooping last-member-query-interval
seconds
ip igmp snooping querier
ip-address
ip igmp snooping report-suppression
ip igmp snooping mrouter interface
interface
ip igmp snooping static-group
group-ip-addr
[
source
source-ip-addr
]
interface
interface
ip igmp snooping link-local-groups-suppression
ip igmp snooping v3-report-suppression
(Optional)
copy running-config startup-config
To display the IGMP snooping configuration information, perform one of the following tasks:
show ip igmp snooping groups [ source [ group ] | group [ source ]] [ vlan vlan-id ] [ detail ] |
|
Displays IGMP snooping explicit tracking information by VLAN. |
For detailed information about the fields in the output from these commands, see the Cisco Nexus 3548 Switch NX-OS Multicast Routing Command Reference .
Use the show ip igmp snooping statistics vlan command to display IGMP snooping statistics.
Use the clear ip igmp snooping statistics vlan command to clear IGMP snooping statistics.
For detailed information about using these commands, see the Cisco Nexus 3548 Switch NX-OS Multicast Routing Command Reference .
This example shows how to configure the IGMP snooping parameters:
For additional information related to implementing IGMP snooping, see the following sections:
Table 5-3 lists the release history for this feature.