Cisco Nexus 1000V Layer 2 Switching Configuration Guide, Release 4.0(4)SV1(3)
Configuring IGMP Snooping
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Configuring IGMP Snooping

Table Of Contents

Configuring IGMP Snooping

Information about IGMP Snooping

IGMP Snooping

IGMPv1 and IGMPv2

IGMPv3

IGMP Snooping Query Feature

Prerequisites for IGMP Snooping

Default Settings

Configuring IGMP Snooping

Verifying the IGMP Snooping Configuration

Example Configuration for IGMP Snooping

Additional References

Related Documents

Standards

Feature History for IGMP Snooping


Configuring IGMP Snooping


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

Default Settings

Configuring IGMP Snooping

Verifying the IGMP Snooping Configuration

Example Configuration for IGMP Snooping

Additional References

Feature History for IGMP Snooping

Information about IGMP Snooping

This section includes the following topics:

IGMP Snooping

IGMPv1 and IGMPv2

IGMPv3

IGMP Snooping Query Feature

IGMP Snooping

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.

IGMPv1 and IGMPv2

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.


IGMPv3

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.

IGMP Snooping Query Feature

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.

Prerequisites for IGMP Snooping

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.

Default Settings

Table 5-1 lists the default settings for IGMP snooping parameters.

Table 5-1 Default IGMP Snooping Parameters 

Parameters
Default

IGMP snooping

Enabled

IGMPv3 Explicit tracking

Enabled

IGMPv2 Fast leave

Disabled

Last member query interval

1 second

Snooping querier

Disabled

IGMPv1/v2 Report suppression

Disabled

IGMPv3 Report suppression

Disabled


Configuring IGMP Snooping

Use this procedure to configure IGMP snooping.

BEFORE YOU BEGIN

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.

Table 5-2 IGMP Snooping Parameters 

Parameter
Description

IGMP snooping

Enables IGMP snooping globally or on a per-VLAN basis. The default is enabled.

Note If the global setting is disabled, then all VLANs are treated as disabled, whether they are enabled or not.

Explicit tracking

Tracks IGMPv3 membership reports from individual hosts for each port on a per-VLAN basis. The default is enabled.

Fast leave

Enables the software to remove the group state when it receives an IGMP Leave report without sending an IGMP query message. This parameter is used for IGMPv2 hosts when no more than one host is present on each VLAN port. The default is disabled.

Last member query interval

Sets the interval the software waits after sending an IGMP query to verify that no hosts that want to receive a particular multicast group remain on a network segment. If no hosts respond before the last member query interval expires, the software removes the group from the associated VLAN port. Values range from 1 to 25 seconds. The default is 1 second.

Report suppression

Limits the membership report traffic sent to multicast-capable routers. When you disable report suppression, all IGMP reports are sent as is to multicast-capable routers. The default is disabled.

Multicast router

Configures a static connection to a multicast router. The interface to the router must be in the selected VLAN.

Static group

Configures a Layer 2 port of a VLAN as a static member of a multicast group.



Note Be aware that the NX-OS commands may differ from those used in Cisco IOS.


SUMMARY STEPS

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

DETAILED STEPS

 
Command
Purpose

Step 1 

config t


Example:

n1000v# config t

n1000v(config)#

Enters global configuration mode.

Step 2 

ip igmp snooping


Example:

n1000v(config)# ip igmp snooping

n1000v(config)#

Enables IGMP snooping in the running configuration. The default is enabled.

Note If disabled, then IGMP snooping on all VLANs is disabled, whether IGMP snooping is enabled on a VLAN or not.

Step 3 

vlan vlan-id


Example:

n1000v(config)# vlan 2

n1000v(config-vlan)#

Enters global configuration mode for the specified VLAN.

Step 4 

ip igmp snooping


Example:

n1000v(config-vlan)# ip igmp snooping

Enables IGMP snooping for the specific VLAN in the running configuration.

The default is enabled.

 

ip igmp snooping explicit-tracking


Example:

n1000v(config-vlan)# ip igmp snooping explicit-tracking

n1000v(config-vlan)#

Tracks IGMPv3 membership reports from individual hosts for each port on a per-VLAN basis in the running configuraiton.

The default is enabled on all VLANs.

 

ip igmp snooping fast-leave


Example:

n1000v(config-vlan)# ip igmp snooping fast-leave

n1000v(config-vlan)#

Enables fast-leave for the specified VLAN in the running configuration.

Fast-leave supports IGMPv2 hosts that cannot be explicitly tracked because of the host report suppression mechanism of the IGMPv2 protocol.

When you enable fast leave, the IGMP software assumes that no more than one host is present on each VLAN port.

The default is disabled for all VLANs.

 

ip igmp snooping last-member-query-interval seconds


Example:

n1000v(config-vlan)# ip igmp snooping last-member-query-interval 3

n1000v(config-vlan)#

Establishes a time interval in seconds after which the group is removed from the associated VLAN port if no hosts respond to an IGMP query message. This interval is saved in the running configuration

Allowable intervals are from 1 (default) to 25 seconds.

 

ip igmp snooping mrouter interface interface


Example:

n1000v(config-vlan)# ip igmp snooping mrouter interface ethernet 2/1

n1000v(config-vlan)#

Configures a static connection to a multicast router in the running configuraiton.

The interface to the router must be in the specified VLAN. You can specify the interface by the type and the number, such as ethernet slot/port.

 

ip igmp snooping static-group group-ip-addr interface interface


Example:

n1000v(config-vlan)# ip igmp snooping static-group 230.0.0.1 interface ethernet 2/1

n1000v(config-vlan)#

Configures a Layer 2 port of a VLAN as a static member of a multicast group in the running configuration.

You can specify the interface by the type and the number, such as ethernet slot/port.

Step 5 

copy running-config startup-config


Example:

n1000v# copy running-config startup-config

(Optional) Saves the running configuration persistently through reboots and restarts by copying it to the startup configuration.

Verifying the IGMP Snooping Configuration

Use the following commands to display the IGMP snooping configuration information.

Command
Purpose

show ip igmp snooping [vlan vlan-id]

Displays IGMP snooping configuration by VLAN.

show ip igmp snooping groups [vlan vlan-id] [detail]

Displays IGMP snooping information about groups by VLAN.

show ip igmp snooping querier [vlan vlan-id]

Displays IGMP snooping queriers by VLAN.

show ip igmp snooping mroute [vlan vlan-id]

Displays multicast router ports by VLAN.

show ip igmp snooping explicit-tracking [vlan vlan-id]

Displays IGMP snooping explicit tracking information by VLAN.


For detailed information about commands and their output, see the Cisco Nexus 1000V Command Reference, Release 4.0(4)SV1(3).

Example Configuration for IGMP Snooping

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#

Additional References

For additional information related to implementing IGMP snooping, see the following sections:

Related Documents

Standards

Related Documents

Related Topic
Document Title

Port Profiles

Cisco Nexus 1000V Port Profile Configuration Guide, Release 4.0(4)SV1(3)

Interfaces

Cisco Nexus 1000V Interface Configuration Guide, Release 4.0(4)SV1(3)

Complete command syntax, command modes, command history, defaults, usage guidelines, and examples

Cisco Nexus 1000V Command Reference, Release 4.0(4)SV1(3)


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.


Feature History for IGMP Snooping

This section provides the release history for the IGMP snooping feature.

Table 5-3

Feature Name
Releases
Feature Information

IGMP Snooping

4.0(4)SV1(1)

This feature was introduced.

Report suppression

4.0(4)SV1(3)

Removed support for report suppression.