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This chapter describes how to configure Internet Group Management Protocol (IGMP) snooping.
This chapter includes the following topics:
•Information about IGMP Snooping
•Prerequisites for IGMP Snooping
•Verifying the IGMP Snooping Configuration
•Example Configuration for IGMP Snooping
•Feature History for IGMP Snooping
This section includes the following topics:
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 device.
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.
The Cisco Nexus 1000V IGMP snooping implementation has the following proprietary features:
•Source filtering that allows forwarding of multicast packets based on destination and source IP.
•Multicast forwarding based on IP address rather than MAC address.
•Optimized multicast flooding (OMF) that forwards unknown traffic to routers only and performs no data driven state creation.
For more information about IGMP snooping, see RFC 4541.
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 time-out to indicate that no hosts remain that want to receive multicast data for a particular group.
Report suppression is not supported and is disabled by default.
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 Nexus 1000V 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 queries.
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 time-out, the software removes the group state.
When the multicast traffic does not need to be routed, you must configure an external switch to query membership. On the external switch, define the query feature in a VLAN that contains multicast sources and receivers but no other active query feature.
When an IGMP snooping query feature is enabled, it sends out periodic IGMP queries that trigger IGMP report messages from hosts wanting to receive IP multicast traffic. IGMP snooping listens to these IGMP reports to identify accurate forwarding.
IGMP snooping has the following prerequisites:
•You are logged in to the switch.
•A querier must be running on the uplink switches on the VLANs that contain multicast sources and receivers.
Table 5-1 lists the default settings for IGMP snooping parameters.
Use this procedure to configure IGMP snooping.
Before beginning this procedure, you must know or do the following:
•You are logged in to the CLI in EXEC mode.
Note Be aware that the NX-OS commands may differ from those used in Cisco IOS.
•Table 5-2 lists and describes the configurable IGMP snooping parameters.
Note Be aware that the NX-OS commands may differ from those used in Cisco IOS.
1. config t
2. ip igmp snooping
3. vlan vlan-id
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 mrouter interface interface
ip igmp snooping static-group group-ip-addr interface interface
5. copy running-config startup-config
Use the following commands to display the IGMP snooping configuration information.
For detailed information about commands and their output, see the Cisco Nexus 1000V Command Reference, Release 4.0(4)SV1(3).
The following example shows how to configure the IGMP snooping parameters:
n1000v# config t
n1000v(config)# ip igmp snooping
n1000v(config)# vlan 2
n1000v(config-vlan)# ip igmp snooping
n1000v(config-vlan)# ip igmp snooping explicit-tracking
n1000v(config-vlan)# ip igmp snooping mrouter interface ethernet 2/1
n1000v(config-vlan)# ip igmp snooping static-group 230.0.0.1 interface ethernet 2/1
n1000v(config-vlan)# copy run start
[########################################] 100%
n1000v(config-vlan)# exit
n1000v(config)# exit
n1000v#
For additional information related to implementing IGMP snooping, see the following sections:
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No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
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This section provides the release history for the IGMP snooping feature.
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IGMP Snooping |
4.0(4)SV1(1) |
This feature was introduced. |
Report suppression |
4.0(4)SV1(3) |
Removed support for report suppression. |