As shown in Figure 1, when IGMP snooping is not enabled, the AC floods multicast packets to all hosts in a VLAN. When IGMP snooping is enabled, the AC forwards multicast packets of known multicast groups only to the receivers.

Figure 1 Multicast packet transmission without and with IGMP snooping

IGMP snooping ports

As shown in Figure 2, IGMP snooping runs on Device A and Device B, and Host A and Host C are receivers in a multicast group. IGMP snooping ports are divided into member ports and router ports.

Figure 2 IGMP snooping ports

Router ports

On an IGMP snooping Layer 2 device, the ports toward Layer 3 multicast devices are called router ports. In Figure 2, GigabitEthernet 1/0/1 of Device A and GigabitEthernet 1/0/1 of Device B are router ports.

Router ports contain the following types:

· Dynamic router port—When a port receives an IGMP general query whose source address is not 0.0.0.0, the port is added into the dynamic router port list. At the same time, an aging timer is started for the port. If the port receives an IGMP general query before the timer expires, the timer is reset. If the port does not receive an IGMP general query when the timer expires, the port is removed from the dynamic router port list.

· Static router port—When a port is statically configured as a router port, it is added into the static router port list. The static router port does not age out, and it can be deleted only manually.

Do not confuse the "router port" in IGMP snooping with the "routed interface" commonly known as the "Layer 3 interface." The router port in IGMP snooping is a Layer 2 interface.

Member ports

On an IGMP snooping Layer 2 device, the ports toward receiver hosts are called member ports. In Figure 2, GigabitEthernet 1/0/2 and GigabitEthernet 1/0/3 of Device A and GigabitEthernet 1/0/2 of Device B are member ports.

Member ports contain the following types:

· Dynamic member port—When a port receives an IGMP report, it is added to the associated dynamic IGMP snooping forwarding entry as an outgoing interface. At the same time, an aging timer is started for the port. If the port receives an IGMP report before the timer expires, the timer is reset. If the port does not receive an IGMP report when the timer expires, the port is removed from the associated dynamic forwarding entry.

· Static member port—When a port is statically configured as a member port, it is added to the associated static IGMP snooping forwarding entry as an outgoing interface. The static member port does not age out, and it can be deleted only manually.

Unless otherwise specified, router ports and member ports in this document include both static and dynamic router ports and member ports.

How IGMP snooping works

The ports in this section are dynamic ports. For information about how to configure and remove static ports, see "Configuring static ports."

IGMP messages types include general query, IGMP report, and leave message. An IGMP snooping-enabled Layer 2 device performs differently depending on the message types.

General query

The IGMP querier periodically sends IGMP general queries to all hosts and routers on the local subnet to check for the existence of multicast group members.

After receiving an IGMP general query, the Layer 2 device forwards the query to all ports in the VLAN except the receiving port. The Layer 2 device also performs one of the following actions:

· If the receiving port is a dynamic router port in the dynamic router port list, the Layer 2 device restarts the aging timer for the port.

· If the receiving port does not exist in the dynamic router port list, the Layer 2 device adds the port to the dynamic router port list. It also starts an aging timer for the port.

IGMP report

A host sends an IGMP report to the IGMP querier for the following purposes:

· Responds to queries if the host is a multicast group member.

· Applies for a multicast group membership.

After receiving an IGMP report from a host, the Layer 2 device forwards the report through all the router ports in the VLAN. It also resolves the address of the reported multicast group, and looks up the forwarding table for a matching entry as follows:

· If no match is found, the Layer 2 device creates a forwarding entry with the receiving port as an outgoing interface. It also marks the receiving port as a dynamic member port and starts an aging timer for the port.

· If a match is found but the matching forwarding entry does not contain the receiving port, the Layer 2 device adds the receiving port to the outgoing interface list. It also marks the receiving port as a dynamic member port and starts an aging timer for the port.

· If a match is found and the matching forwarding entry contains the receiving port, the Layer 2 device restarts the aging timer for the port.

In an application with a group policy configured on an IGMP snooping-enabled Layer 2 device, when a user requests a multicast program, the user's host initiates an IGMP report. After receiving this report, the Layer 2 device resolves the multicast group address in the report and performs ACL filtering on the report. If the report passes ACL filtering, the Layer 2 device creates an IGMP snooping forwarding entry for the multicast group with the receiving port as an outgoing interface. Otherwise, the Layer 2 device drops this report, in which case the multicast data for the multicast group is not sent to this port, and the user cannot retrieve the program.

A Layer 2 device does not forward an IGMP report through a non-router port because of the host IGMP report suppression mechanism.

Leave message

An IGMPv1 receiver host does not send any leave messages when it leaves a multicast group. The Layer 2 device cannot immediately update the status of the port that connects to the receiver host. The Layer 2 device does not remove the port from the outgoing interface list in the associated forwarding entry until the aging time for the group expires.

An IGMPv2 or IGMPv3 host sends an IGMP leave message when it leaves a multicast group.

When the Layer 2 device receives an IGMP leave message on a dynamic member port, the Layer 2 device first examines whether a forwarding entry matches the group address in the message.

· If no match is found, the Layer 2 device discards the IGMP leave message.

· If a match is found but the receiving port is not an outgoing interface in the forwarding entry, the Layer 2 device discards the IGMP leave message.

· If a match is found and the receiving port is not the only outgoing interface in the forwarding entry, the Layer 2 device performs the following actions:

¡ Discards the IGMP leave message.

¡ Sends an IGMP group-specific query to identify whether the group has active receivers attached to the receiving port.

¡ Sets the aging timer for the receiving port to twice the IGMP last member query interval.

· If a match is found and the receiving port is the only outgoing interface in the forwarding entry, the Layer 2 device performs the following actions:

¡ Forwards the IGMP leave message to all router ports in the VLAN.

¡ Sends an IGMP group-specific query to identify whether the group has active receivers attached to the receiving port.

¡ Sets the aging timer for the receiving port to twice the IGMP last member query interval.

After receiving the IGMP leave message on a port, the IGMP querier resolves the multicast group address in the message. Then, it sends an IGMP group-specific query to the multicast group through the receiving port.

After receiving the IGMP group-specific query, the Layer 2 device forwards the query through all its router ports in the VLAN and all member ports of the multicast group. Then, it waits for the responding IGMP report from the directly connected hosts. For the dynamic member port that received the leave message, the Layer 2 device also performs one of the following actions:

· If the port receives an IGMP report before the aging timer expires, the Layer 2 device resets the aging timer.

· If the port does not receive an IGMP report when the aging timer expires, the Layer 2 device removes the port from the forwarding entry for the multicast group.

Protocols and standards

RFC 4541, Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches

Compatibility information

Feature and hardware compatibility

Hardware series	Model	IGMP snooping compatibility
WX1800H series	WX1804H WX1810H WX1820H	Yes
WX2500H series	WX2510H WX2540H WX2560H	Yes
WX3000H series	WX3010H WX3010H-L WX3010H-X WX3024H WX3024H-L	Yes: · WX3010H · WX3010H-X · WX3024H No: · WX3024H · WX3024H-L
WX3500H series	WX3508H WX3510H WX3520H WX3540H	Yes
WX5500E series	WX5510E WX5540E	Yes
WX5500H series	WX5540H WX5560H WX5580H	Yes
Access controller modules	EWPXM1MAC0F EWPXM1WCME0 EWPXM2WCMD0F LSQM1WCMX20 LSQM1WCMX40 LSUM1WCME0 LSUM1WCMX20RT LSUM1WCMX40RT	Yes

Command and hardware compatibility

The WX1800H series, WX2500H series, and WX3000H series access controllers do not support the slot keyword or the slot-number argument.

IGMP snooping configuration task list

Tasks at a glance
Configuring basic IGMP snooping features: · (Required.) Enabling IGMP snooping · (Optional.) Specifying an IGMP snooping version · (Optional.) Setting the maximum number of IGMP snooping forwarding entries · (Optional.) Setting the IGMP last member query interval
(Optional.) Configuring IGMP snooping port features: · Setting aging timers for dynamic ports · Configuring static ports · Configuring a port as a simulated member host · Enabling fast-leave processing · Disabling a port from becoming a dynamic router port
(Optional.) Configuring the IGMP snooping querier: · Enabling the IGMP snooping querier · Configuring parameters for IGMP general queries and responses
(Optional.) Configuring parameters for IGMP messages: · Configuring source IP addresses for IGMP messages · Setting the 802.1p priority for IGMP messages
(Optional.) Configuring IGMP snooping policies: · Configuring a multicast group policy · Enabling dropping unknown multicast data · Enabling IGMP report suppression · Setting the maximum number of multicast groups on a port · Enabling the multicast group replacement feature

Tasks at a glance

Configuring basic IGMP snooping features:

· (Required.) Enabling IGMP snooping

· (Optional.) Specifying an IGMP snooping version

· (Optional.) Setting the maximum number of IGMP snooping forwarding entries

· (Optional.) Setting the IGMP last member query interval

(Optional.) Configuring IGMP snooping port features:

· Setting aging timers for dynamic ports

· Configuring static ports

· Configuring a port as a simulated member host

· Enabling fast-leave processing

· Disabling a port from becoming a dynamic router port

(Optional.) Configuring the IGMP snooping querier:

· Enabling the IGMP snooping querier

· Configuring parameters for IGMP general queries and responses

(Optional.) Configuring parameters for IGMP messages:

· Configuring source IP addresses for IGMP messages

· Setting the 802.1p priority for IGMP messages

(Optional.) Configuring IGMP snooping policies:

· Configuring a multicast group policy

· Enabling dropping unknown multicast data

· Enabling IGMP report suppression

· Setting the maximum number of multicast groups on a port

· Enabling the multicast group replacement feature

The IGMP snooping configurations made on Layer 2 aggregate interfaces do not interfere with the configurations made on member ports. In addition, the configurations made on Layer 2 aggregate interfaces do not take part in aggregation calculations. The configuration made on a member port of the aggregate group takes effect after the port leaves the aggregate group.

Configuring basic IGMP snooping features

Before you configure basic IGMP snooping features, complete the following tasks:

· Configure VLANs.

· Determine the IGMP snooping version.

· Determine the maximum number of IGMP snooping forwarding entries.

· Determine the IGMP last member query interval.

Enabling IGMP snooping

When you enable IGMP snooping, follow these restrictions and guidelines:

· You must enable IGMP snooping globally before you enable it for a VLAN.

· IGMP snooping configuration made in VLAN view takes effect only on the member ports in that VLAN.

· You can enable IGMP snooping for the specified VLANs in IGMP-snooping view or for a VLAN in VLAN view. For a VLAN, the configuration in VLAN view has the same priority as the configuration in IGMP-snooping view, and the most recent configuration takes effect.

To enable IGMP snooping for the specified VLANs:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable IGMP snooping globally and enter IGMP-snooping view.	igmp-snooping	By default, IGMP snooping is globally disabled.
3. Enable IGMP snooping for the specified VLANs.	enable vlan vlan-list	By default, IGMP snooping is disabled for a VLAN.

To enable IGMP snooping for a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable IGMP snooping globally and enter IGMP-snooping view.	igmp-snooping	By default, IGMP snooping is globally disabled.
3. Return to system view.	quit	N/A
4. Enter VLAN view.	vlan vlan-id	N/A
5. Enable IGMP snooping for the VLAN.	igmp-snooping enable	By default, IGMP snooping is disabled in a VLAN.

Specifying an IGMP snooping version

Different IGMP snooping versions process different versions of IGMP messages.

· IGMPv2 snooping processes IGMPv1 and IGMPv2 messages, but it floods IGMPv3 messages in the VLAN instead of processing them.

· IGMPv3 snooping processes IGMPv1, IGMPv2, and IGMPv3 messages.

If you change IGMPv3 snooping to IGMPv2 snooping, the device does the following:

· Clears all IGMP snooping forwarding entries that are dynamically added.

· Keeps static IGMPv3 snooping forwarding entries (*, G).

· Clears static IGMPv3 snooping forwarding entries (S, G), which will be restored when IGMP snooping is switched back to IGMPv3 snooping.

For more information about static IGMP snooping forwarding entries, see "Configuring static ports."

You can specify the version for the specified VLANs in IGMP-snooping view or for a VLAN in VLAN view. For a VLAN, the configuration in VLAN view has the same priority as the configuration in IGMP-snooping view, and the most recent configuration takes effect.

To specify an IGMP snooping version for the specified VLANs:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable IGMP snooping globally and enter IGMP-snooping view.	igmp-snooping	N/A
3. Specify an IGMP snooping version for the specified VLANs.	version version-number vlan vlan-list	The default setting is 2.

To specify an IGMP snooping version for a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Specify an IGMP snooping version for the VLAN.	igmp-snooping version version-number	The default setting is 2.

Setting the maximum number of IGMP snooping forwarding entries

You can modify the maximum number of IGMP snooping forwarding entries, including dynamic entries and static entries. When the number of forwarding entries on the device reaches the upper limit, the device does not automatically remove any existing entries. To allow new entries to be created, H3C recommends that you manually remove some entries.

To set the maximum number of IGMP snooping forwarding entries:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Set the maximum number of IGMP snooping forwarding entries.	entry-limit limit	The default setting is 4294967295.

Setting the IGMP last member query interval

A receiver host starts a report delay timer for a multicast group when it receives an IGMP group-specific query for the group. This timer is set to a random value in the range of 0 to the maximum response time advertised in the query. When the timer value decreases to 0, the host sends an IGMP report to the group.

The IGMP last member query interval defines the maximum response time advertised in IGMP group-specific queries. Set an appropriate value for the IGMP last member query interval to speed up hosts' responses to IGMP group-specific queries and avoid IGMP report traffic bursts.

Configuration restrictions and guidelines

When you set the IGMP last member query interval, follow these restrictions and guidelines:

· The Layer 2 device does not send an IGMP group-specific query if it receives an IGMP leave message from a port enabled with fast-leave processing.

· You can set the IGMP last member query interval globally for all VLANs in IGMP-snooping view or for a VLAN in VLAN view. For a VLAN, the VLAN-specific configuration takes priority over the global configuration.

Setting the IGMP last member query interval globally

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Set the IGMP last member query interval globally.	last-member-query-interval interval	The default setting is 1 second.

Setting the IGMP last member query interval in a VLAN

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Set the IGMP last member query interval for the VLAN.	igmp-snooping last-member-query-interval interval	The default setting is 1 second.

Configuring IGMP snooping port features

Before you configure IGMP snooping port features, complete the following tasks:

· Enable IGMP snooping for the VLAN.

· Determine the aging timer for dynamic router ports.

· Determine the aging timer for dynamic member ports.

· Determine the addresses of the multicast group and multicast source.

Setting aging timers for dynamic ports

When you set aging timers for dynamic ports, follow these restrictions and guidelines:

· If the memberships of multicast groups frequently change, you can set a relatively small value for the aging timer of the dynamic member ports. If the memberships of multicast groups rarely change, you can set a relatively large value.

· IGMP group-specific queries originated by the Layer 2 device trigger the adjustment of aging timers for dynamic member ports. If a dynamic member port receives such a query, its aging timer is set to twice the IGMP last member query interval. For more information about setting the IGMP last member query interval on the Layer 2 device, see "Setting the IGMP last member query interval."

· You can set the timers globally for all VLANs in IGMP-snooping view or for a VLAN in VLAN view. For a VLAN, the VLAN-specific configuration takes priority over the global configuration.

Setting the aging timers for dynamic ports globally

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Set the aging timer for dynamic router ports globally.	router-aging-time interval	The default setting is 260 seconds.
4. Set the global aging timer for dynamic member ports globally.	host-aging-time interval	The default setting is 260 seconds.

Setting the aging timers for dynamic ports in a VLAN

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Set the aging timer for dynamic router ports in the VLAN.	igmp-snooping router-aging-time interval	The default setting is 260 seconds.
4. Set the aging timer for dynamic member ports in the VLAN.	igmp-snooping host-aging-time interval	The default setting is 260 seconds.

Configuring static ports

You can configure the following types of static ports:

· Static member port—When you configure a port as a static member port for a multicast group, all hosts attached to the port will receive multicast data for the group.

The static member port does not respond to IGMP queries. When you complete or cancel this configuration on a port, the port does not send an unsolicited IGMP report or leave message.

· Static router port—When you configure a port as a static router port for a multicast group, all multicast data for the group received on the port will be forwarded.

To configure static ports:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Configure the port as a static port.	· Configure the port as a static member port: igmp-snooping static-group group-address [ source-ip source-address ] vlan vlan-id · Configure the port as a static router port: igmp-snooping static-router-port vlan vlan-id	By default, a port is not a static member port or a static router port.

Configuring a port as a simulated member host

When a port is configured as a simulated member host, it is equivalent to an independent host in the following ways:

· It sends an unsolicited IGMP report when you complete the configuration.

· It responds to IGMP general queries with IGMP reports.

· It sends an IGMP leave message when you cancel the configuration.

The version of IGMP running on the simulated member host is the same as the version of IGMP snooping running on the port. The port ages out in the same way as a dynamic member port.

To configure a port as a simulated member host:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Configure the port as a simulated member host.	igmp-snooping host-join group-address [ source-ip source-address ] vlan vlan-id	By default, the port is not a simulated member host.

Enabling fast-leave processing

This feature enables the device to immediately remove a port from the forwarding entry for a multicast group when the port receives a leave massage.

Configuration restrictions and guidelines

When you enable fast-leave processing, follow these restrictions and guidelines:

· Do not enable fast-leave processing on a port that has multiple receiver hosts in a VLAN. If fast-leave processing is enabled, after a receiver host leaves a multicast group, the other receivers cannot receive multicast data for the group.

· You can enable fast-leave processing globally for all ports in IGMP-snooping view or for a port in interface view. For a port, the port-specific configuration takes priority over the global configuration.

Configuration procedure

To enable fast-leave processing globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Enable fast-leave processing globally.	fast-leave [ vlan vlan-list ]	By default, fast-leave processing is disabled.

To enable fast-leave processing on a port:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Enable fast-leave processing on the port.	igmp-snooping fast-leave [ vlan vlan-list ]	By default, fast-leave processing is disabled.

Disabling a port from becoming a dynamic router port

A receiver host might send IGMP general queries for testing purposes. On the Layer 2 device, the port that receives the messages becomes a dynamic router port. Before the aging timer for the port expires, the following problems might occur:

· All multicast data for the VLAN to which the port belongs flows to the port. Then, the port forwards the data to attached receiver hosts. The receiver hosts will receive unexpected multicast data.

· The port forwards the IGMP general queries to its upstream multicast routers. These messages might affect the multicast routing protocol state (such as the IGMP querier or DR election) on the multicast routers. This might further cause network interruption.

To solve these problems, you can disable a port from becoming a dynamic router port. This also improves network security and the control over receiver hosts.

To disable a port from becoming a dynamic router port:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Disable the port from becoming a dynamic router port.	igmp-snooping router-port-deny [ vlan vlan-list ]	By default, a port can become a dynamic router port. This configuration does not affect the static router port configuration.

Configuring the IGMP snooping querier

This section describes how to configure an IGMP snooping querier.

Configuration prerequisites

Before you configure the IGMP snooping querier, complete the following tasks:

· Enable IGMP snooping for the VLAN.

· Determine the IGMP general query interval.

· Determine the maximum response time for IGMP general queries.

Enabling the IGMP snooping querier

This feature enables the device to periodically send IGMP general queries to establish and maintain multicast forwarding entries at the data link Layer. You can configure an IGMP snooping querier on a network without Layer 3 multicast devices.

Do not enable the IGMP snooping querier on a network that runs IGMP. An IGMP snooping querier does not take part in IGMP querier elections. However, it might affect IGMP querier elections if it sends IGMP general queries with a low source IP address.

To enable the IGMP snooping querier:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Enable the IGMP snooping querier.	igmp-snooping querier	By default, the IGMP snooping querier is disabled.

Configuring parameters for IGMP general queries and responses

CAUTION:

To avoid mistakenly delete multicast group members, make sure the IGMP general query interval is greater than the maximum response time for IGMP general queries.

You can modify the IGMP general query interval based on the actual condition of the network.

A receiver host starts a report delay timer for each multicast group that it has joined when it receives an IGMP general query. This timer is set to a random value in the range of 0 to the maximum response time advertised in the query. When the timer value decreases to 0, the host sends an IGMP report to the corresponding multicast group.

Set an appropriate value for the maximum response time for IGMP general queries to speed up hosts' responses to IGMP general queries and avoid IGMP report traffic bursts.

You can set the maximum response time for IGMP general queries globally for all VLANs in IGMP-snooping view or for a VLAN in VLAN view. For a VLAN, the VLAN-specific configuration takes priority over the global configuration.

Configuring parameters for IGMP general queries and responses globally

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Set the maximum response time for IGMP general queries.	max-response-time interval	The default setting is 10 seconds.
4. Set the IGMP last member query interval.	last-member-query-interval interval	The default setting is 1 second.

Configuring parameters for IGMP general queries and responses in a VLAN

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Set the IGMP general query interval in the VLAN.	igmp-snooping query-interval interval	The default setting is 125 seconds.
4. Set the maximum response time for IGMP general queries in the VLAN.	igmp-snooping max-response-time interval	The default setting is 10 seconds.

Configuring parameters for IGMP messages

This section describes how to configure parameters for IGMP messages.

Configuration prerequisites

Before you configure parameters for IGMP messages, complete the following tasks:

· Enable IGMP snooping for the VLAN.

· Determine the source IP address of IGMP general queries.

· Determine the source IP address of IGMP group-specific queries.

· Determine the source IP address of IGMP reports.

· Determine the source IP address of IGMP leave messages.

· Determine the 802.1p priority of IGMP messages.

Configuring source IP addresses for IGMP messages

The IGMP snooping querier might send IGMP general queries with the source IP address 0.0.0.0. The port that receives such queries will not be maintained as a dynamic router port. This might prevent the associated dynamic IGMP snooping forwarding entry from being correctly created at the data link layer and eventually cause multicast traffic forwarding failures.

To avoid this problem, you can configure a non-all-zero IP address as the source IP address of the IGMP queries on the IGMP snooping querier. This configuration might affect the IGMP querier election within the subnet.

You can also change the source IP address of IGMP reports or leave messages sent by a simulated member host or an IGMP snooping proxy.

To configure source IP addresses for IGMP messages:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Configure the source IP address for IGMP general queries.	igmp-snooping general-query source-ip ip-address	By default, the source IP address of IGMP general queries is the IP address of the current VLAN interface. If the current VLAN interface does not have an IP address, the source IP address is 0.0.0.0.
4. Configure the source IP address for IGMP group-specific queries.	igmp-snooping special-query source-ip ip-address	By default, the source IP address of IGMP group-specific queries is one of the following: · The source address of IGMP group-specific queries if the IGMP snooping querier of the VLAN has received IGMP general queries. · The IP address of the current VLAN interface if the IGMP snooping querier does not receive an IGMP general query. · 0.0.0.0 if the IGMP snooping querier does not receive an IGMP general query and the current VLAN interface does not have an IP address.
5. Configure the source IP address for IGMP reports.	igmp-snooping report source-ip ip-address	By default, the source IP address of IGMP reports is the IP address of the current VLAN interface. If the current VLAN interface does not have an IP address, the source IP address is 0.0.0.0.
6. Configure the source IP address for IGMP leave messages.	igmp-snooping leave source-ip ip-address	By default, the source IP address of IGMP leave messages is the IP address of the current VLAN interface. If the current VLAN interface does not have an IP address, the source IP address is 0.0.0.0.

Setting the 802.1p priority for IGMP messages

When congestion occurs on outgoing ports of the Layer 2 device, it forwards IGMP messages in their 802.1p priority order, from highest to lowest. You can assign a higher 802.1p priority to IGMP messages that are created or forwarded by the device.

You can set the 802.1p priority globally for all VLANs in IGMP-snooping view or for a VLAN in VLAN view. For a VLAN, the VLAN-specific configuration takes priority over the global configuration.

Setting the 802.1p priority for IGMP messages globally

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Set the 802.1p priority for IGMP messages.	dot1p-priority priority-number	The default setting is 0.

Setting the 802.1p priority for IGMP messages in a VLAN

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Set the 802.1p priority for IGMP messages in the VLAN.	igmp-snooping dot1p-priority priority-number	The default setting is 0.

Configuring IGMP snooping policies

Before you configure IGMP snooping policies, complete the following tasks:

· Enable IGMP snooping for the VLAN.

· Determine the ACL used by the multicast group policy.

· Determine the maximum number of multicast groups that a port can join.

Configuring a multicast group policy

This feature enables the device to filter IGMP reports by using an ACL that specifies the multicast groups and the optional sources. It is used to control the multicast groups that hosts can join.

Configuration restrictions and guidelines

When you configure a multicast group policy, follow these restrictions and guidelines:

· This configuration takes effect only on the multicast groups that ports join dynamically.

· You can configure a multicast group policy globally for all ports in IGMP-snooping view or for a port in interface view. For a port, the port-specific configuration takes priority over the global configuration.

Configuration procedure

To configure a multicast group policy globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Configure a multicast group policy globally.	group-policy acl-number [ vlan vlan-list ]	By default, no multicast group policies exist. Hosts can join any multicast groups.

To configure a multicast group policy on a port:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Configure a multicast group policy on the port.	igmp-snooping group-policy acl-number [ vlan vlan-list ]	By default, no multicast group policies exist on a port. Hosts attached to the port can join any multicast groups.

Enabling dropping unknown multicast data

This feature enables the device to drop all unknown multicast data. Unknown multicast data refers to multicast data for which no forwarding entries exist in the IGMP snooping forwarding table.

If you do not enable this feature, the unknown multicast data is flooded in the VLAN to which the data belongs.

Configuration restrictions and guidelines

When you enable dropping unknown multicast data, follow these restrictions and guidelines:

· You can enable dropping unknown multicast data globally for all VLANs in IGMP-snooping view or for a VLAN in VLAN view. The drop-unknown command in IGMP-snooping view and the igmp-snooping drop-unknown command in VLAN view are mutually exclusive. You cannot configure them on the same device.

· For a VLAN enabled with this feature, some device models drop unknown IPv6 multicast data for the VLAN.

· For a VLAN enabled with this feature, some device models still forward unknown IPv4 multicast data for the VLAN to other router ports in the VLAN.

Configuration procedure

To enable dropping unknown multicast data globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Enable dropping unknown multicast data globally.	drop-unknown	By default, dropping unknown multicast data is disabled. Unknown multicast data is flooded.

To enable dropping unknown multicast data for a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Enable dropping unknown multicast data for the VLAN.	igmp-snooping drop-unknown	By default, dropping unknown multicast data is disabled. Unknown multicast data is flooded.

Enabling IGMP report suppression

This feature enables the device to forward only the first IGMP report for a multicast group to its directly connected Layer 3 device. Other reports for the same group in the same query interval are discarded. This reduces the multicast traffic.

To enable IGMP report suppression:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Enable IGMP report suppression.	report-aggregation	By default, IGMP report suppression is enabled.

Setting the maximum number of multicast groups on a port

You can set the maximum number of multicast groups on a port to regulate the port traffic.

Configuration restrictions and guidelines

When you set the maximum number of multicast groups on a port, follow these restrictions and guidelines:

· This configuration takes effect only on the multicast groups that a port joins dynamically.

· If the number of multicast groups on a port exceeds the limit, the system removes all the forwarding entries related to that port. The receiver hosts attached to that port can join multicast groups again before the number of multicast groups on the port reaches the limit.

Configuration procedure

To set the maximum number of multicast groups on a port:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Set the maximum number of multicast groups on a port.	igmp-snooping group-limit limit [ vlan vlan-list ]	The default setting is 4294967295.

Enabling the multicast group replacement feature

This feature enables the device to replace an existing group with a newly joined group when the number of groups exceeds the upper limit. This feature is typically used in the channel switching application. Without this feature, the Layer 2 device discards IGMP reports for new groups, and the user cannot change to the new channel.

Configuration restrictions and guidelines

When you enable the multicast group replacement feature, follow these restrictions and guidelines:

· This configuration takes effect only on the multicast groups that a port joins dynamically.

· You can enable this feature globally for all ports in IGMP-snooping view or for a port in interface view. For a port, the port-specific configuration takes priority over the global configuration.

Configuration procedure

To enable the multicast group replacement feature globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Enable the multicast group replacement feature globally.	overflow-replace [ vlan vlan-list ]	By default, the multicast group replacement feature is disabled.

To enable the multicast group replacement feature on a port:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Enable multicast group replacement feature on a port.	igmp-snooping overflow-replace [ vlan vlan-list ]	By default, the multicast group replacement feature is disabled.

Displaying and maintaining IGMP snooping

Execute display commands in any view and reset commands in user view.

Task	Command
Display IGMP snooping status.	display igmp-snooping [ global \| vlan vlan-id ]
Display dynamic IGMP snooping group entries.	display igmp-snooping group [ group-address \| source-address ] * [ vlan vlan-id ] [ verbose ] [ slot slot-number ]
Display dynamic router port information.	display igmp-snooping router-port [ vlan vlan-id ] [ slot slot-number ]
Display static IGMP snooping group entries.	display igmp-snooping static-group [ group-address \| source-address ] * [ vlan vlan-id ] [ verbose ] [ slot slot-number ]
Display static router port information.	display igmp-snooping static-router-port [ vlan vlan-id ] [ slot slot-number ]
Display statistics for the IGMP messages learned by IGMP snooping.	display igmp-snooping statistics
Display information about Layer 2 IP multicast groups.	display l2-multicast ip [ group group-address \| source source-address ] * [ vlan vlan-id ] [ slot slot-number ]
Display Layer 2 IP multicast group entries.	display l2-multicast ip forwarding [ group group-address \| source source-address ] * [ vlan vlan-id ] [ slot slot-number ]
Display information about Layer 2 MAC multicast groups.	display l2-multicast mac [ mac-address ] [ vlan vlan-id ] [ slot slot-number ]
Display Layer 2 MAC multicast group entries.	display l2-multicast mac forwarding [ mac-address ] [ vlan vlan-id ] [ slot slot-number ]
Clear dynamic IGMP snooping group entries.	reset igmp-snooping group { group-address [ source-address ] \| all } [ vlan vlan-id ]
Clear dynamic router port information.	reset igmp-snooping router-port { all \| vlan vlan-id }
Clear statistics for IGMP messages learned through IGMP snooping.	reset igmp-snooping statistics

IGMP snooping configuration example

Network requirements

As shown in Figure 3:

· The source sends multicast traffic to multicast group 224.1.1.1.

· The client is a receiver host of the multicast group.

· The route between the source and the client is reachable.

Configure the AC so that the client can receive the multicast traffic from the source.

Figure 3 Network diagram

Configuration procedure

Configuring Router A

# Enable IP multicast routing globally, and enable PIM-DM and IGMP on the port that connects to the AC. (Details not shown.)

Configuring the AC

1. Configure WLAN services:

# Create VLAN 100.

<AC> system-view

[AC] vlan 100

[AC-vlan100] quit

# Create service template 1, and set the SSID to Multicast for the service template.

[AC] wlan service-template 1

[AC-wlan-st-1] ssid Multicast

# Bind VLAN 100 to service template 1, and enable the service template.

[AC-wlan-st-1] vlan 100

[AC-wlan-st-1] service-template enable

[AC-wlan-st-1] quit

# Create an AP named ap with model WA4320i-ACN, and set the serial ID of the AP to 219801A0CNC138011454.

[AC] wlan ap ap model WA4320i-ACN

[AC-wlan-ap-ap] serial-id 219801A0CNC138011454

# Bind service template 1 to radio 1, and enable radio 1 for AP ap.

[AC-wlan-ap-ap] radio 1

[AC-wlan-ap-ap-radio-1] service-template 1

[AC-wlan-ap-ap-radio-1] radio enable

[AC-wlan-ap-ap-radio-1] quit

[AC-wlan-ap-ap]quit

2. Configure IGMP snooping:

# Enable IGMP snooping globally.

[AC] igmp-snooping

[AC-igmp-snooping] quit

# In VLAN 100, enable IGMP snooping, and specify IGMP snooping version 3.

[AC] vlan 100

[AC-vlan100] igmp-snooping enable

[AC-vlan100] igmp-snooping version 3

[AC-vlan100] quit

3. Configure Ethernet interfaces.

# Configure GigabitEthernet 1/0/2 on the access controller as a trunk port, and assign the port to VLAN 100.

[AC] interface GigabitEthernet 1/0/2

[AC-GigabitEthernet1/0/2] port link-type trunk

[AC-GigabitEthernet1/0/2] port trunk permit vlan 100

[AC-GigabitEthernet1/0/2] quit

Configuring the client

# Configure the client to access the WLAN service with the SSID Multicast and request multicast traffic for multicast group 224.1.1.1. (Details not shown.)

Verifying the configuration

# Display detailed information about dynamic IGMP snooping group entries for VLAN 100 on the AC.

[AC] display igmp-snooping group vlan 100 verbose

Total 1 entries.

VLAN 100: Total 1 entries.

(0.0.0.0, 224.1.1.1)

Attribute: local port

FSM information: normal

Host slots (0 in total):

Host ports (1 in total):

WLAN-BSS1/0/20 (00:03:23)

The output shows that WLAN-BSS 1/0/20 on the AC has joined multicast group 224.1.1.1.

Troubleshooting IGMP snooping

Layer 2 multicast forwarding cannot function

Symptom

Layer 2 multicast forwarding cannot function on the Layer 2 device.

Solution

To resolve the problem:

1. Use the display igmp-snooping command to display IGMP snooping status.

2. If IGMP snooping is not enabled, use the igmp-snooping command in system view to enable IGMP snooping globally. Then, use the igmp-snooping enable command in VLAN view to enable IGMP snooping for the VLAN.

3. If IGMP snooping is enabled globally but not enabled for the VLAN, use the igmp-snooping enable command in VLAN view to enable IGMP snooping for the VLAN.

4. If the problem persists, contact H3C Support.

Multicast group policy does not work

Symptom

Hosts can receive multicast data from multicast groups that are not permitted by the multicast group policy.

Solution

To resolve the problem:

1. Use the display acl command to verify that the configured ACL meets the multicast group policy requirements.

2. Use the display this command in IGMP-snooping view or in a corresponding interface view to verify that the correct multicast group policy has been applied. If the applied multicast group policy is not correct, use the group-policy or igmp-snooping group-policy command to apply the correct multicast group policy.

3. Use the display igmp-snooping command to verify that dropping unknown multicast data is enabled. If dropping unknown multicast data is not enabled, use the drop-unknown or igmp-snooping drop-unknown command to enable dropping unknown multicast data.

4. If the problem persists, contact H3C Support.

08-IP Multicast

Overview

Router ports

Member ports

General query

IGMP report

Leave message

Protocols and standards

Enabling IGMP snooping

Specifying an IGMP snooping version

Configuration restrictions and guidelines

Setting the IGMP last member query interval globally

Setting the IGMP last member query interval in a VLAN

Setting aging timers for dynamic ports

Setting the aging timers for dynamic ports globally

Setting the aging timers for dynamic ports in a VLAN

Configuring a port as a simulated member host

Configuration restrictions and guidelines

Configuration procedure

Disabling a port from becoming a dynamic router port

Configuring the IGMP snooping querier

Enabling the IGMP snooping querier

Configuring parameters for IGMP general queries and responses globally

Configuring source IP addresses for IGMP messages

Setting the 802.1p priority for IGMP messages globally

Setting the 802.1p priority for IGMP messages in a VLAN

Configuring IGMP snooping policies

Configuring a multicast group policy

Configuration restrictions and guidelines

Configuration procedure

Enabling dropping unknown multicast data

Configuration restrictions and guidelines

Configuration procedure

Enabling IGMP report suppression

Configuration restrictions and guidelines

Configuration procedure

Enabling the multicast group replacement feature

Configuration restrictions and guidelines

Configuration procedure

Displaying and maintaining IGMP snooping

IGMP snooping configuration example

Configuring Router A

Configuring the AC

Configuring the client

Troubleshooting IGMP snooping

Layer 2 multicast forwarding cannot function

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Solution

Symptom

Solution

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