Layer 2 Switching Configuration Guide, Cisco DCNM for LAN, Release 5.x
Configuring IGMP Snooping
Downloads: This chapterpdf (PDF - 460.0KB) The complete bookPDF (PDF - 4.22MB) | Feedback

Configuring IGMP Snooping

Configuring IGMP Snooping

This chapter describes how to configure IGMP snooping on Cisco NX-OS devices using the Cisco Data Center Network Manager (DCNM) for LAN.


Note


The Cisco NX-OS release that is running on a managed device may not support all the features or settings described in this chapter. For the latest feature information and caveats, see the documentation and release notes for your platform and software release.


This chapter includes the following sections:

Information About IGMP Snooping


Note


We recommend that you do not disable IGMP snooping on the device. If you disable IGMP snooping, you may see reduced multicast performance because of excessive false flooding within the device.


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.

This figure 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 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 NX-OS IGMP snooping software has the following proprietary features:


  • Source filtering that allows forwarding of multicast packets based on the destination and source IP address.

  • Multicast forwarding based on the IP address rather than the MAC address.

  • Optimized multicast flooding (OMF) that forwards unknown traffic to routers only and performs no data driven state creation.

IGMPv1 and IGMPv2

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, 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, 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.


IGMPv3

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 device 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 device 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.

IGMP Snooping Querier

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 Snooping with VDCs and VRFs

A virtual device context (VDC) is a logical representation of a set of system resources. Within each VDC, you can define multiple virtual routing and forwarding (VRF) instances. One IGMP process can run per VDC. The IGMP process supports all VRFs in that VDC and performs the function of IGMP snooping within that VDC.

Licensing Requirements for IGMP Snooping

The following table shows the licensing requirements for this feature:

Product

Description

Cisco DCNM

IGMP snooping requires no license. Any feature not included in a license package is bundled with the Cisco DCNM and is provided at no charge to you.

However, using VDCs requires an Advanced Services license.

Platform Support for IGMP Snooping

The following platform supports this feature. For platform-specific information, including guidelines and limitations, system defaults, and configuration limits, see the corresponding documentation.

Platform

Documentation

Cisco Nexus 7000 Series switches

Cisco Nexus 7000 Series switch documentation

Cisco Nexus 4000 Series switches

Cisco Nexus 4000 Series switch documentation

Configuring IGMP Snooping

You configure IGMP snooping globally or per VLAN on the Cisco Nexus 7000 Series devices using the IGMP Snooping pane. You can also view the IGMP snooping status per VLAN.


Note


If IGMP snooping is disabled for the device and enabled for specified VLANs, the functionality is disabled for the VLAN as well.

However, if IGMP snooping is disabled for the VLAN and enabled for the device, the functionality remains disabled for the VLAN.

Report suppression and IGMPv3 report suppression function the same way.


Configuring IGMP Snooping Global Parameters

You can configure IGMP snooping global parameters.

Procedure
Step 1   From the Feature Selector pane, choose Switching > Spanning Tree > Multicast > IGMP Snooping to open the IGMP Snooping pane.
Step 2   In the Summary pane, click the device to set the IGMP snooping globally for the entire device.
Step 3   In the Details pane, click the Device Details tab.
Step 4   From the IGMP Snooping drop-down list, choose Enabled or Disabled.

IGMP Snooping is enabled by default.

Step 5   From the Report Suppression drop-down list, choose Enabled or Disabled.

Report Suppression is enabled by default.

Step 6   From the IGMPv3 Report Suppression drop-down list, choose Enabled or Disabled.

IGMPv3 Report Suppression is disabled by default globally for the entire device.

Step 7   From the Link-local Group Suppression drop-down list, choose Enabled or Disabled.

Link-Local Group Suppression is enabled by default.

Step 8   In the Event History Buffer Settings area, from the drop-down lists, choose disabled, small, medium, or large for each of the following:

  • vPC
  • IGMP Snoop Internal
  • MFDM-Sum

  • MFDM

  • VLAN

  • VLAN Events

The default buffer sizes for vPC, IGMP Snoop Internal, MFDM-Sum, and MFDM are small. The default buffer sizes for VLAN and VLAN Events are medium.

Step 9   (Optional)From the menu bar, choose File > Deploy to apply your changes to the device.

Configuring IGMP Snooping Parameters per VLAN

You can configure IGMP snooping parameters per VLAN.

Procedure
Step 1   From the Feature Selector pane, choose Switching > Multicast > IGMP Snooping to open the IGMP Snooping pane.
Step 2   In the Summary pane, click the device that has the VLANs for which you want to configure IGMP snooping.
Step 3   Click the VLAN for which you want to configure IGMP snooping.
Step 4   In the Details pane, click the Details tab.

The VLAN ID box displays the VLAN number that you are working on.

Step 5   From the IGMP Snooping drop-down list, choose Enabled or Disabled.

IGMP Snooping is enabled per VLAN by default

Step 6   From the Report Suppression drop-down list, choose Enabled or Disabled.

Report Suppression is enabled per VLAN by default.

Step 7   From the IGMPv3 Report Suppression drop-down list, choose Enabled or Disabled.

IGMPv3 Report Suppression is enabled per VLAN by default. Once you enable IGMPv3 Report Suppression for the entire device, you do not have to enable that feature for each VLAN.

Step 8   From the Link-local Group Suppression drop-down list, choose Enabled or Disabled.

Link-Local Group Suppression is enabled per VLAN by default

Step 9   From the Fast Leave drop-down list, choose Enabled or Disabled.

Fast Leave is disabled per VLAN by default.

Step 10   From the Explicit Tracking drop-down list, choose Enabled or Disabled.

Explicit tracking is enabled per VLAN by default.

Step 11   Enter the number of seconds that you want in the Last Member Query Interval field.

The default value for Last Member Query Interval is 1 second for each VLAN, and the maximum value is 25 seconds.

Step 12   (Optional) Enter the IP address for IGMP snooping querier for the switch.
Step 13   (Optional) Right-click in the Static Multicast Group area and choose Add Row or Delete.
  1. Click Delete to delete a static multicast group.
  2. Optional: To add a static multicast group, enter the IP address of the multicast source in the Source Address field, the IP address of the multicast group in the Group Address field, and the interface joining the group in the Interface field.
    Note   

    Ethernet and port channel are the supported interfaces for this field.

Step 14   (Optional)Right-click in the Static Multicast Router area and choose Add Row or Delete.
  1. Click Delete to delete an interface to a static multicast router.
  2. To add an interface to the static multicast router, choose the interface from the drop-down list in the Interface field and click OK.
    Note   

    Ethernet and port channel are the supported interfaces for this field.

Step 15   (Optional)From the menu bar, choose File > Deploy to apply your changes to the device.

Viewing IGMP Snooping Status per VLAN

You can view the status of the IGMP multicast groups, the IGMP multicast routers, the IGMP snooping explicit tracking feature, and the IGMP snooping querier.

Procedure
Step 1   From the Feature Selector pane, choose Switching > Multicast > IGMP Snooping to open the IGMP Snooping pane.
Step 2   In the Summary pane, click the device that has the VLANs for which you want to view the IGMP snooping status.
Step 3   Click the VLAN for which you want to view IGMP snooping.
Step 4   In the Details pane, click the Status tab.
Step 5   Click the Multicast Groups section.

The section expands to allow you to Refresh the display and displays the following information for each multicast group discovered using IGMP snooping: Group Address, Source Address, IGMP Version, the Type of multicast group, and the Interfaces that have shown interest in this multicast group.

Step 6   Click the Multicast Routers section.

The section expands to allow you to Refresh the display and displays the following information for each multicast router: Interface connected to the multicast router, Type, Up Time for the entry, and Expiry Time for the entry.

Step 7   Click the Explicit Tracking section.

The section expands to allow you to Refresh the display and displays the following explicit tracking information for each VLAN: Source Address for the multicast traffic, multicast Group Address, Interface that has shown interest in the multicast traffic, Reporter Address of the host machine that has shown interest in the multicast traffic, Up Time for the entry, Last Join Time, and Expiry Time for the entry.

Step 8   Click the Querier section.

The section expands to allow you to Refresh the display and displays the following IGMP snooping information for each VLAN: IP Address of the querier, IGMP Version, Expiry Time for the entry, and Interface on which the querier is discovered.


Field Descriptions for Configuring IGMP Snooping

IGMP Snooping: Device: Device Details Tab

Table 1 IGMP Snooping: Device: Device Details Tab

Field

Description

IGMP Snooping

Whether IGMP snooping is enabled or not on the device. The default value is enabled.

Report Suppression

Whether IGMP report suppression is enabled or not on the device. The default value is enabled.

IGMPv3 Report Suppression

Whether IGMPv3 report suppression is enabled or not on the device. The default value is disabled.

Link-local Group Suppression

Whether link-local group suppression is enabled or not on the device. The default value is enabled.

Event History Buffer Setting

vPC

Event history buffer size for a virtual port channel (vPC). Valid values are as follows:
  • disabled

  • small

  • medium

  • large

The default value is small.

IGMP Snoop Internal

Event history buffer size for IGMP snoop internal. Valid values are as follows:
  • disabled

  • small

  • medium

  • large

The default value is small.

MFDM-Sum

Event history buffer size for an MFDM sum. Valid values are as follows:
  • disabled

  • small

  • medium

  • large

The default value is small.

MFDM

Event history buffer size for an MFDM. Valid values are as follows:
  • disabled

  • small

  • medium

  • large

The default value is small.

VLAN

Event history buffer size for a VLAN. Valid values are as follows:
  • disabled

  • small

  • medium

  • large

The default value is medium.

VLAN Events

Event history buffer size for VLAN events. Valid values are as follows:
  • disabled

  • small

  • medium

  • large

The default value is medium.

RIB

Event history buffer size for a RIB. Valid values are as follows:
  • disabled

  • small

  • medium

  • large

The default value is small.

IGMP Snooping: VLAN: Details Tab

Table 2 IGMP Snooping: VLAN: Details Tab

Field

Description

VLAN ID

Display only. VLAN that you are configuring.

IGMP Snooping

Whether IGMP snooping is enabled or not on the VLAN. The default is enabled.

Report Suppression

Whether report suppression is enabled or not on the VLAN. The default value is enabled.

IGMPv3 Report Suppression

Whether IGMPv3 report suppression is enabled or not on the VLAN. The default value is enabled.

Link-local Group Suppression

Whether link-local group suppression is enabled or not on the VLAN. The default value is enabled.

Fast Leave

Whether fast leave is enabled or not on the VLAN. The default value is disabled.

Explicit Tracking

Whether explicit tracking is enabled or not on the VLAN. The default value is enabled.

Last Member Query Interval

Last member query interval in seconds. The range is from 1 to 25 seconds, and the default value is 1.

Switch Querier

IP address for the switch querier.

Static Multicast Group

Source Address

IP address of the multicast source.

Group Address

IP address of the multicast group.

Interface

Interface on which the multicast group/source is configured.

Static Multicast Router

Interface

Interface on which the multicast router is configured.

IGMP Snooping: VLAN: Status: Multicast Groups Section

Table 3 IGMP Snooping: VLAN: Status: Multicast Groups Section

Field

Description

Last Refresh Time

Display only. Time that the display was last refreshed.

Group Address

Display only. Multicast group address snooped by IGMP snooping.

Source Address

Display only. Multicast source address snooped by IGMP snooping.

IGMP Version

Display only. IGMP version. Valid values are as follows:

Type

Display only. Type of multicast group address discovered. Valid values are as follows:
  • S--static

  • D--dynamic

  • R--router port

Interface

List of interfaces that have shown interest in the multicast group.

IGMP Snooping: VLAN: Status: Multicast Routers Section

Table 4 IGMP Snooping: VLAN: Status: Multicast Routers Section

Field

Description

Last Refresh Time

Display only. Time that the display was last refreshed.

Interface

Display only. Interface connected to the multicast router.

Type

Display only. Type of interface connected to the multicast router. Valid values are as follows:
  • S--static

  • D--dynamic

  • V--vPC peer link

  • I--internal

Up Time

Display only. Time that the entry has been up.

Expiry Time

Display only. Time at which this entry expires.

IGMP Snooping: VLAN: Status: Explicit Tracking Section

Table 5 IGMP Snooping: VLAN: Status: Explicit Tracking Section

Field

Description

Last Refresh Time

Display only. Time that the display was last refreshed.

Source Address

Display only.Source address for the multicast traffic.

Group Address

Display only. Multicast group address.

Interface

Display only. Interface that has shown interest in receiving the multicast traffic.

Reporter Address

Display only. Host machine that has shown interest in receiving the multicast traffic.

Up Time

Display only. Time this entry has been up.

Last Join Time

Display only. Time when this entry was added.

Expiry Time

Display only. Time at which this entry expires.

IGMP Snooping: VLAN: Status: Querier Section

Table 6 IGMP Snooping: VLAN: Status: Querier Section

Field

Description

Last Refresh Time

Display only. Time that the display was last refreshed.

Querier Address

Display only. IP address of the querier.

IGMP Version

Display only. IGMP version. Valid values are as follows:

Expiry Time

Display only. Time at which this entry expires.

Interface

Display only. Interface on which the querier is defined or discovered. The value will be Self if the local device is configured as the querier.

Feature History for Configuring IGMP Snooping

This table lists the release history for this feature.
Table 7 Feature History for Configuring IGMP Snooping

Feature Name

Releases

Feature Information

IGMP snooping

5.0(2)

This feature was introduced.