Contents

Configuring MLD snooping· 1

Overview· 1

MLD snooping ports· 1

How MLD snooping works· 3

Protocols and standards· 4

General configuration restrictions and guidelines· 4

MLD snooping configuration task list 5

Configuring basic MLD snooping features· 5

Enabling MLD snooping· 5

Specifying an MLD snooping version· 6

Setting the maximum number of MLD snooping forwarding entries· 7

Setting the MLD last listener query interval 7

Configuring MLD snooping port features· 8

Setting aging timers for dynamic ports· 8

Configuring static ports· 9

Configuring a port as a simulated member host 9

Enabling fast-leave processing· 10

Disabling a port from becoming a dynamic router port 11

Configuring the MLD snooping querier 11

Configuration prerequisites· 11

Enabling the MLD snooping querier 11

Configuring parameters for MLD general queries and responses· 12

Configuring parameters for MLD messages· 13

Configuration prerequisites· 13

Configuring source IPv6 addresses for MLD messages· 13

Setting the 802.1p priority for MLD messages· 14

Configuring MLD snooping policies· 15

Configuring an IPv6 multicast group policy· 15

Enabling IPv6 multicast source port filtering· 16

Enabling dropping unknown IPv6 multicast data· 16

Enabling MLD report suppression· 17

Setting the maximum number of IPv6 multicast groups on a port 17

Enabling IPv6 multicast group replacement 18

Displaying and maintaining MLD snooping· 19

MLD snooping configuration examples· 20

IPv6 group policy and simulated joining configuration example· 20

Static port configuration example· 22

MLD snooping querier configuration example· 25

Troubleshooting MLD snooping· 27

Layer 2 multicast forwarding cannot function· 27

IPv6 multicast group policy does not work· 27

 

Configuring MLD snooping

Overview

MLD snooping runs on a Layer 2 device as an IPv6 multicast constraining mechanism to improve multicast forwarding efficiency. It creates Layer 2 multicast forwarding entries from MLD messages that are exchanged between the hosts and the router.

As shown in Figure 1, when MLD snooping is not enabled, the Layer 2 switch floods IPv6 multicast packets to all hosts in a VLAN. When MLD snooping is enabled, the Layer 2 switch forwards multicast packets of known IPv6 multicast groups to only the receivers.

Figure 1 IPv6 multicast packet transmission processes without and with MLD snooping

 

MLD snooping ports

As shown in Figure 2, MLD snooping runs on Switch A and Switch B, and Host A and Host C are receiver hosts in an IPv6 multicast group. MLD snooping ports are divided into member ports and router ports.

Figure 2 MLD snooping ports

 

Router ports

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

Router ports contain the following types:

·     Dynamic router port—When a port receives an MLD general query whose source address is not 0::0 or receives an IPv6 PIM hello message, 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 either of the messages before the timer expires, the timer is reset. If the port does not receive either of the messages 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 MLD snooping with the "routed interface" commonly known as the "Layer 3 interface." The router port in MLD snooping is a Layer 2 interface.

Member ports

On an MLD 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 Switch A and GigabitEthernet 1/0/2 of Switch B are member ports.

Member ports contain the following types:

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

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

MLD messages include general query, MLD report, and done message. An MLD snooping-enabled switch performs differently depending on the MLD message types.

General query

The MLD querier periodically sends MLD general queries to all hosts and routers on the local subnet to check for the existence of IPv6 multicast group members.

After receiving an MLD 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 router 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.

MLD report

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

·     Responds to queries if the host is an IPv6 multicast group member.

·     Applies for an IPv6 multicast group membership.

After receiving an MLD report from a host, the Layer 2 device forwards the report through all the router ports in the VLAN. It also resolves the IPv6 address of the reported IPv6 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 for the group with the receiving port 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 port as a dynamic member port to the forwarding entry 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 an IPv6 multicast group policy configured on an MLD snooping-enabled Layer 2 device, when a user requests a multicast program, the user's host initiates an MLD report. After receiving this report message, the Layer 2 device resolves the IPv6 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 MLD snooping forwarding entry for the group with the receiving port as an outgoing interface. If the report does not pass ACL filtering, the Layer 2 device drops this report message. The IPv6 multicast data for the IPv6 multicast group is not sent to this port, and the user cannot retrieve the program.

A Layer 2 device does not forward an MLD report through a non-router port because of the MLD report suppression mechanism. For more information about the host MLD report suppression mechanism, see "Configuring MLD."

Done message

When a host leaves an IPv6 multicast group, the host sends an MLD done message to the Layer 3 devices. When the Layer 2 device receives the MLD done message on a dynamic member port, the Layer 2 device first examines whether a forwarding entry matches the IPv6 multicast group address in the message.

·     If no match is found, the Layer 2 device discards the MLD done 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 MLD done 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 MLD done message.

¡     Sends an MLD multicast-address-specific query to identify whether the group has active listeners attached to the receiving port.

¡     Sets the aging timer for the receiving port to twice the MLD last listener 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 MLD done message to all router ports in the VLAN.

¡     Sends an MLD multicast-address-specific query to identify whether the group has active listeners attached to the receiving port.

¡     Sets the aging timer for the receiving port to twice the MLD last listener query interval.

After receiving the MLD done message on a port, the MLD querier resolves the IPv6 multicast group address in the message. Then, it sends an MLD multicast-address-specific query to the IPv6 multicast group through the receiving port.

After receiving the MLD multicast-address-specific query, the Layer 2 device forwards the query through all its router ports in the VLAN and all member ports of the IPv6 multicast group. Then, it waits for the responding MLD report from the directly connected hosts. For the dynamic member port that received the done message, the Layer 2 device also performs one of the following actions:

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

·     If the port does not receive any MLD report messages when the aging timer expires, the Layer 2 device removes the port from the forwarding entry for the IPv6 multicast group.

Protocols and standards

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

General configuration restrictions and guidelines

When you configure MLD snooping, follow these restrictions and guidelines:

·     For a VLAN configured with MLD snooping, if you change the VPN instance bound to the VLAN interface, Layer 2 multicast traffic for the VLAN is interrupted. In this case, you must execute the reset mld-snooping group command so that new MLD snooping forwarding entries can be created.

·     For MLD reports received from secondary VLANs, the relevant MLD snooping forwarding entries are maintained by the primary VLAN. Therefore, you need to configure MLD snooping only for the primary VLAN. The configuration made in secondary VLANs will not take effect. For more information about primary VLANs and secondary VLANs, see Layer 2—LAN Switching Configuration Guide.

·     The MLD 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.

MLD snooping configuration task list

Tasks at a glance
Configuring basic MLD snooping features: ·     (Required.) Enabling MLD snooping ·     (Optional.) Specifying an MLD snooping version ·     (Optional.) Setting the maximum number of MLD snooping forwarding entries ·     (Optional.) Setting the MLD last listener query interval
Configuring MLD snooping port features: ·     (Optional.) Setting aging timers for dynamic ports ·     (Optional.) Configuring static ports ·     (Optional.) Configuring a port as a simulated member host ·     (Optional.) Enabling fast-leave processing ·     (Optional.) Disabling a port from becoming a dynamic router port
Configuring the MLD snooping querier: ·     (Optional.) Enabling the MLD snooping querier ·     (Optional.) Configuring parameters for MLD general queries and responses
Configuring parameters for MLD messages: ·     (Optional.) Configuring source IPv6 addresses for MLD messages ·     (Optional.) Setting the 802.1p priority for MLD messages
Configuring MLD snooping policies: ·     (Optional.) Configuring an IPv6 multicast group policy ·     (Optional.) Enabling IPv6 multicast source port filtering ·     (Optional.) Enabling dropping unknown IPv6 multicast data ·     (Optional.) Enabling MLD report suppression ·     (Optional.) Setting the maximum number of IPv6 multicast groups on a port ·     (Optional.) Enabling IPv6 multicast group replacement

 

Configuring basic MLD snooping features

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

·     Configure VLANs.

·     Determine the MLD snooping version.

·     Determine the maximum number of MLD snooping forwarding entries.

·     Determine the MLD last listener query interval.

Enabling MLD snooping

When you enable MLD snooping, follow these guidelines:

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

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

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

Enabling MLD snooping for the specified VLANs

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

 

Enabling MLD snooping for a VLAN

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

 

Specifying an MLD snooping version

Different MLD snooping versions can process different versions of MLD messages:

·     MLDv1 snooping can process MLDv1 messages, but it floods MLDv2 messages in the VLAN instead of processing them.

·     MLDv2 snooping can process MLDv1 and MLDv2 messages.

If you change MLDv2 snooping to MLDv1 snooping, the system does the following:

·     Clears all MLD snooping forwarding entries that are dynamically created.

·     Keeps static MLDv2 snooping forwarding entries (*, G).

·     Clears static MLDv2 snooping forwarding entries (S, G), which will be restored when MLD snooping is switched back to MLDv2 snooping.

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

You can specify the version for the specified VLANs in MLD-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 MLD-snooping view, and the most recent configuration takes effect.

Specifying an MLD snooping version for the specified VLANs

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

 

Specifying an MLD 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 MLD snooping version for the VLAN.	mld-snooping version version-number	The default setting is 1.

 

Setting the maximum number of MLD snooping forwarding entries

You can set the maximum number of MLD snooping forwarding entries, including dynamic entries and static entries. When the number of forwarding entries on the switch reaches the upper limit, the switch does not automatically remove any existing entries. As a best practice, manually remove some entries to allow new entries to be created.

To set the maximum number of MLD snooping forwarding entries:

 

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

 

Setting the MLD last listener query interval

A receiver host starts a report delay timer for an IPv6 multicast group when it receives an MLD multicast-address-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 MLD report to the group.

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

Configuration restrictions and guidelines

When you set the MLD last listener query interval, follow these restrictions and guidelines:

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

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

Setting the MLD last listener query interval globally

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

 

Setting the MLD last listener 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 MLD last listener query interval in the VLAN.	mld-snooping last-listener-query-interval interval	The default setting is 1 second.

 

Configuring MLD snooping port features

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

·     Enable MLD 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 IPv6 multicast group and IPv6 multicast source.

Setting aging timers for dynamic ports

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

·     If the memberships of IPv6 multicast groups frequently change, set a relatively small value for the aging timer of the dynamic member ports. If the memberships of IPv6 multicast groups rarely change, you can set a relatively large value.

·     If a dynamic router port receives an IPv6 PIMv2 hello message, the aging timer for the port is specified by the hello message. In this case, the mld-snooping router-aging-time command does not take effect on the port.

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

·     You can set the timers globally for all VLANs in MLD-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 MLD-snooping view.	mld-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 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.	mld-snooping router-aging-time interval	The default setting is 260 seconds.
4.     Set the aging timer for dynamic member ports in the VLAN.	mld-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 an IPv6 multicast group, all hosts attached to the port will receive IPv6 multicast data for the group.

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

·     Static router port—When you configure a port as a static router port for an IPv6 multicast group, all IPv6 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: mld-snooping static-group ipv6-group-address [ source-ip ipv6-source-address ] vlan vlan-id ·     Configure the port as a static router port: mld-snooping static-router-port vlan vlan-id	By default, a port is not a static member port or 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 MLD report when you complete the configuration.

·     It responds to MLD general queries with MLD reports.

·     It sends an MLD done message when you remove the configuration.

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

Configuration procedure

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.	mld-snooping host-join ipv6-group-address [ source-ip ipv6-source-address ] vlan vlan-id	By default, the port is not a simulated member host.

 

Enabling fast-leave processing

This feature enables the switch to immediately remove a port from the forwarding entry for an IPv6 multicast group when the port receives a done message.

Configuration restrictions and guidelines

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

·     Do not enable fast-leave processing on a port that have multiple receiver hosts attached in a VLAN. If fast-leave processing is enabled, after a receiver host leaves an IPv6 multicast group, the other receivers cannot receive IPv6 multicast data for the group.

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

Enabling fast-leave processing globally

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

 

Enabling 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.	mld-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 an MLD general query or IPv6 PIM hello message for testing purposes. In this case, the following problems might exist:

·     The router port that receives the MLD general query or IPv6 PIM hello message becomes a dynamic router port. Before its aging timer expires, this dynamic router port receives all multicast packets within the VLAN that the port belongs to and forwards them to the host attached to the port. In this case, the receiver host will receive IPv6 multicast data that it does not expect.

·     In addition, the MLD general query and IPv6 PIM hello message that the host sends affect the multicast routing protocol state on Layer 3 devices, such as the MLD querier or DR election. This might further cause network interruption.

To solve these problems and to improve network security and the control over multicast users, you can disable the router port from becoming a dynamic router port.

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.	mld-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 MLD snooping querier

This section describes how to configure the MLD snooping querier.

Configuration prerequisites

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

·     Enable MLD snooping for the VLAN.

·     Determine MLD general query interval.

·     Determine the maximum response time for MLD general queries.

Enabling the MLD snooping querier

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

Do not enable the MLD snooping querier on an IPv6 multicast network that runs MLD. An MLD snooping querier does not participate in MLD querier elections. However, it might affect MLD querier elections if it sends MLD general queries with a low source IPv6 address.

To enable the MLD snooping querier 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 the MLD snooping querier.	mld-snooping querier	By default, the MLD snooping querier is disabled.

 

Configuring parameters for MLD general queries and responses

CAUTION: To avoid mistakenly deleting IPv6 multicast group members, make sure the MLD general query interval is greater than the maximum response time for MLD general queries.

 

You can modify the MLD general query interval for a VLAN based on the actual network conditions.

A receiver host starts a report delay timer for each IPv6 multicast group that it has joined when it receives an MLD 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 MLD report to the corresponding IPv6 multicast group.

Configuration restrictions and guidelines

When you configure parameters for MLD general queries and responses, follow these restrictions and guidelines:

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

·     You can set the maximum response time for MLD general queries globally for all VLANs in MLD-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 MLD general queries and responses globally

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter MLD-snooping view.	mld-snooping	N/A
3.     Set the maximum response time for MLD general queries.	max-response-time interval	The default setting is 10 seconds.

 

Configuring parameters for MLD 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 MLD general query interval in the VLAN.	mld-snooping query-interval interval	The default setting is 125 seconds.
4.     Set the maximum response time for MLD general queries in the VLAN.	mld-snooping max-response-time interval	The default setting is 10 seconds.

 

Configuring parameters for MLD messages

This section describes how to configure parameters for MLD messages.

Configuration prerequisites

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

·     Enable MLD snooping for the VLAN.

·     Determine the source IPv6 address of MLD general queries.

·     Determine the source IPv6 address of MLD multicast-address-specific queries.

·     Determine the source IPv6 address of MLD reports.

·     Determine the source IPv6 address of MLD done messages.

·     Determine the 802.1p priority of MLD messages.

Configuring source IPv6 addresses for MLD messages

You can change the source IPv6 address of the MLD queries sent by an MLD snooping querier. This configuration might affect MLD querier election within the subnet.

You can also change the source IPv6 address of MLD reports or done messages sent by a simulated member host or an MLD snooping proxy.

To configure the source IP address for MLD 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.     Configure the source IPv6 address for MLD general queries.	mld-snooping general-query source-ip ipv6-address	By default, the source IPv6 address of MLD general queries is the IPv6 link-local address of the current VLAN interface. If the current VLAN interface does not have an IPv6 link-local address, the source IPv6 address is FE80::02FF:FFFF:FE00:0001.
4.     Configure the source IPv6 address for MLD multicast-address-specific queries.	mld-snooping special-query source-ip ipv6-address	By default, the source IPv6 address of MLD multicast-address-specific queries is one of the following: ·     The source address of MLD general queries if the MLD snooping querier has received MLD general queries. ·     The IPv6 link-local address of the current VLAN interface if the MLD snooping querier does not receive an MLD general query. ·     FE80::02FF:FFFF:FE00:0001 if the MLD snooping querier does not receive an MLD general query and the current VLAN interface does not have an IPv6 link-local address.
5.     Configure the source IPv6 address for MLD reports.	mld-snooping report source-ip ipv6-address	By default, the source IPv6 address of MLD reports is the IPv6 link-local address of the current VLAN interface. If the current VLAN interface does not have an IPv6 link-local address, the source IPv6 address is FE80::02FF:FFFF:FE00:0001.
6.     Configure the source IPv6 address for MLD done messages.	mld-snooping done source-ip ipv6-address	By default, the source IPv6 address of MLD done messages is the IPv6 link-local address of the current VLAN interface. If the current VLAN interface does not have an IPv6 link-local address, the source IPv6 address is FE80::02FF:FFFF:FE00:0001.

 

Setting the 802.1p priority for MLD messages

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

You can configure the 802.1p priority of MLD messages for all VLANs in MLD-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 MLD messages globally

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

 

Setting the 802.1p priority for MLD 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 MLD messages in the VLAN.	mld-snooping dot1p-priority priority-number	The default setting is 0.

 

Configuring MLD snooping policies

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

·     Enable MLD snooping for the VLAN.

·     Determine the ACLs used by the IPv6 multicast group policies.

·     Determine the maximum number of IPv6 multicast groups that a port can join.

Configuring an IPv6 multicast group policy

This feature enables the switch to filter MLD reports based on the used ACL that specifies the IPv6 multicast groups and the optional sources. Use this feature to control the IPv6 multicast groups that receiver hosts can join.

Configuration restrictions and guidelines

When you configure an IPv6 multicast group policy, follow these restrictions and guidelines:

·     This configuration takes effect on the IPv6 multicast groups that ports join dynamically.

·     You can configure an IPv6 multicast group policy globally for all ports in MLD-snooping view or for a port in interface view. For a port, the port-specific configuration takes priority over the global configuration.

Configuring an IPv6 multicast group policy globally

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter MLD-snooping view.	mld-snooping	N/A
3.     Configure an IPv6 multicast group policy globally.	group-policy acl6-number [ vlan vlan-list ]	By default, no IPv6 multicast group policies exist. Receiver host can join any IPv6 multicast groups.

 

Configuring an IPv6 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 an IPv6 multicast group policy for the port.	mld-snooping group-policy acl6-number [ vlan vlan-list ]	By default, no IPv6 multicast group policies exist on a port. Hosts attached to the port can join any IPv6 multicast groups.

 

Enabling IPv6 multicast source port filtering

This feature enables the switch to discard all IPv6 multicast data packets and to accept IPv6 multicast protocol packets. You can enable this feature on ports that connect to only IPv6 multicast receivers.

You can enable multicast source port filtering for the specified ports in MLD-snooping view or for a port in interface view. For a port, the configuration in interface view has the same priority as the configuration in MLD-snooping view, and the most recent configuration takes effect.

Enabling IPv6 multicast source port filtering for the specified ports

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter MLD-snooping view.	mld-snooping	N/A
3.     Enable IPv6 multicast source port filtering globally.	source-deny port interface-list	By default, the IPv6 multicast source port filtering is disabled globally.

 

Enabling IPv6 multicast source port filtering for a port

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter Layer 2 Ethernet interface view.	interface interface-type interface-number	N/A
3.     Enable IPv6 multicast source port filtering on the port.	mld-snooping source-deny	By default, IPv6 multicast source port filtering is disabled on the port.

 

Enabling dropping unknown IPv6 multicast data

This feature enables the switch to drop all unknown IPv6 multicast data. Unknown IPv6 multicast data refers to IPv6 multicast data for which no forwarding entries exist in the MLD snooping forwarding table.

Configuration restrictions and guidelines

When you enable dropping unknown IPv6 multicast data, follow these restrictions and guidelines:

·     To avoid IPv6 multicast forwarding exceptions, do not globally enable this feature when the switch joins an IRF 3 system. For more information about IRF 3, see Virtualization Technologies Configuration Guide.

·     You can enable this feature globally for all VLANs in MLD-snooping view or for a VLAN in VLAN view.

·     The drop-unknown command in MLD-snooping view and the mld-snooping drop-unknown command mutually exclusive. You cannot configure them on the same switch.

·     If you enable dropping unknown IPv6 and IPv4 multicast data, enable both of them globally or for the same VLANs to ensure correct multicast forwarding. For more informational bout enabling dropping unknown IPv4 multicast data, see "Configuring MLD snooping."

·     When dropping unknown IPv6 multicast data is enabled, the switch still forward unknown IPv6 multicast data to other router ports in the VLAN.

Enabling dropping unknown IPv6 multicast data globally

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter MLD-snooping view.	mld-snooping	N/A
3.     Enable dropping unknown IPv6 multicast data globally.	drop-unknown	By default, this feature is disabled. Unknown IPv6 multicast data is flooded in the VLAN to which the data belongs.

 

Enabling dropping unknown IPv6 multicast data in 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 IPv6 multicast data for the VLAN.	mld-snooping drop-unknown	By default, dropping unknown IPv6 multicast data is disabled. Unknown IPv6 multicast data is flooded in the VLAN to which the data belongs.

 

Enabling MLD report suppression

This feature enables the switch to forward only the first MLD report for an IPv6 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 MLD report suppression:

 

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

 

Setting the maximum number of IPv6 multicast groups on a port

You can set the maximum number of IPv6 multicast groups on a port to regulate the port traffic.

Configuration restrictions and guidelines

When you set the maximum number of IPv6 multicast groups on a port, follow these guidelines:

·     This configuration takes effect only on the IPv6 multicast groups that the port joins dynamically.

·     If the number of IPv6 multicast groups on a port exceeds the limit, the system removes all the forwarding entries related to that port. In this case, the receiver hosts attached to that port can join IPv6 multicast groups again before the number of IPv6 multicast groups on the port reaches the limit.

 Configuration procedure

To set the maximum number of IPv6 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 IPv6 multicast groups on the port.	mld-snooping group-limit limit [ vlan vlan-list ]	The default setting is 4294967295.

 

Enabling IPv6 multicast group replacement

This feature enables the switch 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 switch discards MLD reports for new groups, and the user cannot change to the new channel.

Configuration restrictions and guidelines

When you enable IPv6 multicast group replacement, follow these guidelines:

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

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

Enabling IPv6 multicast group replacement globally

Step	Command	Remarks
1.     Enter system view.	system-view	N/A
2.     Enter MLD-snooping view.	mld-snooping	N/A
3.     Enable IPv6 multicast group replacement globally.	overflow-replace [ vlan vlan-list ]	By default, IPv6 multicast group replacement is disabled.

 

Enabling IPv6 multicast group replacement 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 IPv6 multicast group replacement on the port.	mld-snooping overflow-replace [ vlan vlan-list ]	By default, IPv6 multicast group replacement is disabled.

 

Displaying and maintaining MLD snooping

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

 

Task	Command
Display information about Layer 2 IPv6 multicast groups (in standalone mode).	display ipv6 l2-multicast ip [ group ipv6-group-address | source ipv6-source-address ] * [ vlan vlan-id ] [ slot slot-number ]
Display information about Layer 2 IPv6 multicast groups (in IRF mode).	display ipv6 l2-multicast ip [ group ipv6-group-address | source ipv6-source-address ] * [ vlan vlan-id ] [ chassis chassis-number slot slot-number ]
Display Layer 2 IPv6 multicast group entries (in standalone mode).	display ipv6 l2-multicast ip forwarding [ group ipv6-group-address | source ipv6-source-address ] * [ vlan vlan-id ] [ slot slot-number ]
Display Layer 2 IPv6 multicast group entries (in IRF mode).	display ipv6 l2-multicast ip forwarding [ group ipv6-group-address | source ipv6-source-address ] * [ vlan vlan-id ] [ chassis chassis-number slot slot-number ]
Display information about Layer 2 IPv6 MAC multicast groups (in standalone mode).	display ipv6 l2-multicast mac [ mac-address ] [ vlan vlan-id ] [ slot slot-number ]
Display information about Layer 2 IPv6 MAC multicast groups (in IRF mode).	display ipv6 l2-multicast mac [ mac-address ] [ vlan vlan-id ] [ chassis chassis-number slot slot-number ]
Display Layer 2 IPv6 MAC multicast group entries (in standalone mode).	display ipv6 l2-multicast mac forwarding [ mac-address ] [ vlan vlan-id ] [ slot slot-number ]
Display Layer 2 IPv6 MAC multicast group entries (in IRF mode).	display ipv6 l2-multicast mac forwarding [ mac-address ] [ vlan vlan-id ] [ chassis chassis-number slot slot-number ]
Display MLD snooping status.	display mld-snooping [ global | vlan vlan-id ]
Display dynamic MLD snooping forwarding entries (in standalone mode).	display mld-snooping group [ ipv6-group-address | ipv6-source-address ] * [ vlan vlan-id ] [ verbose ] [ slot slot-number ]
Display dynamic MLD snooping forwarding entries (in IRF mode).	display mld-snooping group [ ipv6-group-address | ipv6-source-address ] * [ vlan vlan-id ] [ verbose ] [ chassis chassis-number slot slot-number ]
Display dynamic router port information (in standalone mode).	display mld-snooping router-port [ vlan vlan-id ] [ slot slot-number ]
Display dynamic router port information (in IRF mode).	display mld-snooping router-port [ vlan vlan-id ] [ chassis chassis-number slot slot-number ]
Display static MLD snooping forwarding entries (in standalone mode).	display mld-snooping static-group [ ipv6-group-address | ipv6-source-address ] * [ vlan vlan-id ] [ verbose ] [ slot slot-number ]
Display static MLD snooping forwarding entries (in IRF mode).	display mld-snooping static-group [ ipv6-group-address | ipv6-source-address ] * [ vlan vlan-id ] [ verbose ] [ chassis chassis-number slot slot-number ]
Display static router port information (in standalone mode).	display mld-snooping static-router-port [ vlan vlan-id ] [ slot slot-number ]
Display static router port information (in IRF mode).	display mld-snooping static-router-port [ vlan vlan-id ] [ chassis chassis-number slot slot-number ]
Display statistics for the MLD messages learned through MLD snooping.	display mld-snooping statistics
Clear dynamic MLD snooping forwarding entries.	reset mld-snooping group { ipv6-group-address [ ipv6-source-address ] | all } [ vlan vlan-id ]
Clear dynamic router port information.	reset mld-snooping router-port { all | vlan vlan-id }
Clear statistics for the MLD messages learned through MLD snooping.	reset mld-snooping statistics

 

MLD snooping configuration examples

IPv6 group policy and simulated joining configuration example

Network requirements

As shown in Figure 3, Router A runs MLDv1 and acts as the MLD querier, and Switch A runs MLDv1 snooping.

Configure the group policy and simulate joining to meet the following requirements:

·     Host A and Host B receive only the IPv6 multicast data addressed to IPv6 multicast group FF1E::101. IPv6 multicast data can be forwarded through GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4 of Switch A uninterruptedly, even though Host A and Host B fail to receive the multicast data.

·     Switch A will drop unknown IPv6 multicast data instead of flooding it in VLAN 100.

Figure 3 Network diagram

 

Configuration procedure

1.     Assign an IPv6 address and prefix length to each interface according to Figure 3. (Details not shown.)

2.     Configure Router A:

# Enable IPv6 multicast routing.

<RouterA> system-view

[RouterA] ipv6 multicast routing

[RouterA-mrib6] quit

# Enable MLD on GigabitEthernet 1/0/1.

[RouterA] interface gigabitethernet 1/0/1

[RouterA-GigabitEthernet1/0/1] mld enable

[RouterA-GigabitEthernet1/0/1] quit

# Enable IPv6 PIM-DM on GigabitEthernet 1/0/2.

[RouterA] interface gigabitethernet 1/0/2

[RouterA-GigabitEthernet1/0/2] ipv6 pim dm

[RouterA-GigabitEthernet1/0/2] quit

3.     Configure Switch A:

# Enable MLD snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 1/0/1 through GigabitEthernet 1/0/4 to the VLAN.

[SwitchA] vlan 100

[SwitchA-vlan100] port gigabitethernet 1/0/1 to gigabitethernet 1/0/4

# Enable MLD snooping, and enable dropping IPv6 unknown multicast data for VLAN 100.

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] mld-snooping drop-unknown

[SwitchA-vlan100] quit

# Configure an IPv6 multicast group policy so that the hosts in VLAN 100 can join only IPv6 multicast group FF1E::101.

[SwitchA] acl ipv6 number 2001

[SwitchA-acl6-basic-2001] rule permit source ff1e::101 128

[SwitchA-acl6-basic-2001] quit

[SwitchA] mld-snooping

[SwitchA–mld-snooping] group-policy 2001 vlan 100

[SwitchA–mld-snooping] quit

# Configure GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4 as simulated member hosts to join IPv6 multicast group FF1E::101.

[SwitchA] interface gigabitethernet 1/0/3

[SwitchA-GigabitEthernet1/0/3] mld-snooping host-join ff1e::101 vlan 100

[SwitchA-GigabitEthernet1/0/3] quit

[SwitchA] interface gigabitethernet 1/0/4

[SwitchA-GigabitEthernet1/0/4] mld-snooping host-join ff1e::101 vlan 100

[SwitchA-GigabitEthernet1/0/4] quit

Verifying the configuration

# Send MLD reports from Host A and Host B to join IPv6 multicast groups FF1E::101 and FF1E::202. (Details not shown.)

# Display dynamic MLD snooping forwarding entries for VLAN 100 on Switch A.

[SwitchA] display mld-snooping group vlan 100

Total 1 entries.

 

VLAN 100: Total 1 entries.

  (::, FF1E::101)

    Host slots (0 in total):

    Host ports (2 in total):

      GE1/0/3                              (00:03:23)

      GE1/0/4                              (00:04:10)

The output shows the following information:

·     Host A and Host B have joined IPv6 multicast group FF1E::101 through the member ports GigabitEthernet 1/0/4 and GigabitEthernet 1/0/3 on Switch A, respectively.

·     Host A and Host B have failed to join IPv6 multicast group FF1E::202.

Static port configuration example

Network requirements

As shown in Figure 4:

·     Router A runs MLDv1 and acts as the MLD querier, and Switch A, Switch B, and Switch C run MLDv1 snooping.

·     Host A and Host C are permanent receivers of IPv6 multicast group FF1E::101.

Configure static ports to meet the following requirements:

·     To enhance the reliability of IPv6 multicast traffic transmission, configure GigabitEthernet 1/0/3 and GigabitEthernet 1/0/5 on Switch C as static member ports for IPv6 multicast group FF1E::101.

·     Suppose the STP runs on the network. To avoid data loops, the forwarding path from Switch A to Switch C is blocked. IPv6 multicast data flows to the receivers attached to Switch C only along the path of Switch A—Switch B—Switch C. When this path is blocked, at least one MLD query-response cycle must be completed before IPv6 multicast data flows to the receivers along the path of Switch A—Switch C. In this case, the multicast delivery is interrupted during the process. For more information about the STP, see Layer 2—LAN Switching Configuration Guide.

Configure GigabitEthernet 1/0/3 on Switch A as a static router port. Then, IPv6 multicast data can flow to the receivers nearly uninterrupted along the path of Switch A—Switch C when the path of Switch A—Switch B—Switch C is blocked.

Figure 4 Network diagram

 

Configuration procedure

1.     Assign an IPv6 address and prefix length to each interface according to Figure 4. (Details not shown.)

2.     Configure Router A:

# Enable IPv6 multicast routing.

<RouterA> system-view

[RouterA] ipv6 multicast routing

[RouterA-mrib6] quit

# Enable MLD on GigabitEthernet 1/0/1.

[RouterA] interface gigabitethernet 1/0/1

[RouterA-GigabitEthernet1/0/1] mld enable

[RouterA-GigabitEthernet1/0/1] quit

# Enable IPv6 PIM-DM on GigabitEthernet 1/0/2.

[RouterA] interface gigabitethernet 1/0/2

[RouterA-GigabitEthernet1/0/2] ipv6 pim dm

[RouterA-GigabitEthernet1/0/2] quit

3.     Configure Switch A:

# Enable MLD snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 1/0/1 through GigabitEthernet 1/0/3 to the VLAN.

[SwitchA] vlan 100

[SwitchA-vlan100] port gigabitethernet 1/0/1 to gigabitethernet 1/0/3

# Enable MLD snooping for VLAN 100.

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] quit

# Configure GigabitEthernet 1/0/3 as a static router port.

[SwitchA] interface gigabitethernet 1/0/3

[SwitchA-GigabitEthernet1/0/3] mld-snooping static-router-port vlan 100

[SwitchA-GigabitEthernet1/0/3] quit

4.     Configure Switch B:

# Enable MLD snooping globally.

<SwitchB> system-view

[SwitchB] mld-snooping

[SwitchB-mld-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 to the VLAN.

[SwitchB] vlan 100

[SwitchB-vlan100] port gigabitethernet 1/0/1 gigabitethernet 1/0/2

# Enable MLD snooping for VLAN 100.

[SwitchB-vlan100] mld-snooping enable

[SwitchB-vlan100] quit

5.     Configure Switch C:

# Enable MLD snooping globally.

<SwitchC> system-view

[SwitchC] mld-snooping

[SwitchC-mld-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 1/0/1 through GigabitEthernet 1/0/5 to the VLAN.

[SwitchC] vlan 100

[SwitchC-vlan100] port gigabitethernet 1/0/1 to gigabitethernet 1/0/5

# Enable MLD snooping for VLAN 100.

[SwitchC-vlan100] mld-snooping enable

[SwitchC-vlan100] quit

# Configure GigabitEthernet 1/0/3 and GigabitEthernet 1/0/5 as static member ports for IPv6 multicast group FF1E::101.

[SwitchC] interface gigabitethernet 1/0/3

[SwitchC-GigabitEthernet1/0/3] mld-snooping static-group ff1e::101 vlan 100

[SwitchC-GigabitEthernet1/0/3] quit

[SwitchC] interface gigabitethernet 1/0/5

[SwitchC-GigabitEthernet1/0/5] mld-snooping static-group ff1e::101 vlan 100

[SwitchC-GigabitEthernet1/0/5] quit

Verifying the configuration

# Display static router port information for VLAN 100 on Switch A.

[SwitchA] display mld-snooping static-router-port vlan 100

VLAN 100:

  Router slots (0 in total):

  Router ports (1 in total):

    GE1/0/3

The output shows that GigabitEthernet 1/0/3 on Switch A has become a static router port.

# Display static MLD snooping forwarding entries in VLAN 100 on Switch C.

[SwitchC] display mld-snooping static-group vlan 100

Total 1 entries).

 

VLAN 100: Total 1 entries).

  (::, FF1E::101)

    Host slots (0 in total):

    Host ports (2 in total):

      GE1/0/3

      GE1/0/5

The output shows that GigabitEthernet 1/0/3 and GigabitEthernet 1/0/5 on Switch C have become static member ports of IPv6 multicast group FF1E::101.

MLD snooping querier configuration example

Network requirements

As shown in Figure 5:

·     The network is a Layer 2-only network.

·     Source 1 and Source 2 send multicast data to IPv6 multicast groups FF1E::101 and FF1E::102, respectively.

·     Host A and Host C are receivers of IPv6 multicast group FF1E::101, and Host B and Host D are receivers of IPv6 multicast group FF1E::102.

·     All host receivers run MLDv1 and all switches run MLDv1 snooping. Switch A (which is close to the multicast sources) acts as the MLD snooping querier.

To prevent the switches from flooding unknown IPv6 packets in the VLAN, enable all switches to drop unknown IPv6 multicast packets.

Figure 5 Network diagram

 

Configuration procedure

1.     Configure Switch A:

# Enable MLD snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 1/0/1 through GigabitEthernet 1/0/3 to the VLAN.

[SwitchA] vlan 100

[SwitchA-vlan100] port gigabitethernet 1/0/1 to gigabitethernet 1/0/3

# Enable MLD snooping, and enable dropping unknown IPv6 multicast data packets for VLAN 100.

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] mld-snooping drop-unknown

# Configure Switch A as the MLD snooping querier.

[SwitchA-vlan100] MLD-snooping querier

[SwitchA-vlan100] quit

2.     Configure Switch B:

# Enable MLD snooping globally.

<SwitchB> system-view

[SwitchB] mld-snooping

[SwitchB-mld-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 1/0/1 through GigabitEthernet 1/0/4 to the VLAN.

[SwitchB] vlan 100

[SwitchB-vlan100] port gigabitethernet 1/0/1 to gigabitethernet 1/0/4

# Enable MLD snooping, and enable dropping unknown IPv6 multicast data packets for VLAN 100.

[SwitchB-vlan100] mld-snooping enable

[SwitchB-vlan100] mld-snooping drop-unknown

[SwitchB-vlan100] quit

3.     Configure Switch C:

# Enable MLD snooping globally.

<SwitchC> system-view

[SwitchC] mld-snooping

[SwitchC-mld-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 1/0/1 through GigabitEthernet 1/0/3 to the VLAN.

[SwitchC] vlan 100

[SwitchC-vlan100] port gigabitethernet 1/0/1 to gigabitethernet 1/0/3

# Enable MLD snooping, and enable dropping unknown IPv6 multicast data packets for VLAN 100.

[SwitchC-vlan100] mld-snooping enable

[SwitchC-vlan100] mld-snooping drop-unknown

[SwitchC-vlan100] quit

4.     Configure Switch D:

# Enable MLD snooping globally.

<SwitchD> system-view

[SwitchD] mld-snooping

[SwitchD-mld-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 to the VLAN.

[SwitchD] vlan 100

[SwitchD-vlan100] port gigabitethernet 1/0/1 to gigabitethernet 1/0/2

# Enable MLD snooping, and enable dropping unknown IPv6 multicast data packets for VLAN 100.

[SwitchD-vlan100] mld-snooping enable

[SwitchD-vlan100] mld-snooping drop-unknown

[SwitchD-vlan100] quit

Verifying the configuration

# Display statistics for MLD messages learned through MLD snooping on Switch B.

[SwitchB] display mld-snooping statistics

Received MLD general queries:  3

Received MLDv1 specific queries:  0

Received MLDv1 reports:  12

Received MLD dones:  0

Sent     MLDv1 specific queries:  0

Received MLDv2 reports:  0

Received MLDv2 reports with right and wrong records:  0

Received MLDv2 specific queries:  0

Received MLDv2 specific sg queries:  0

Sent     MLDv2 specific queries:  0

Sent     MLDv2 specific sg queries:  0

Received error MLD messages:  0

The output shows that all switches except Switch A can receive the MLD general queries after Switch A acts as the MLD snooping querier.

Troubleshooting MLD snooping

Layer 2 multicast forwarding cannot function

Symptom

Layer 2 multicast forwarding cannot function through MLD snooping.

Solution

To resolve the problem:

1.     Use the display mld-snooping command to display MLD snooping status.

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

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

4.     If the problem persists, contact H3C Support.

IPv6 multicast group policy does not work

Symptom

Hosts can receive multicast data from IPv6 multicast groups that are not permitted by the IPv6 multicast group policy.

Solution

To resolve the problem:

1.     Use the display acl ipv6 command to verify that the configured IPv6 ACL meets the IPv6 multicast group policy requirements.

2.     Use the display this command in MLD-snooping view or in a corresponding interface view to verify that the correct IPv6 multicast group policy has been correctly applied. If the applied IPv6 multicast group policy is not correct, use the group-policy or mld-snooping group-policy command to apply the correct IPv6 multicast group policy.

3.     Use the display mld-snooping command to verify that dropping unknown IPv6 multicast data is enabled. If this feature is not enabled, use the drop-unknown or mld-snooping drop-unknown command to enable this feature.

4.     If the problem persists, contact H3C Support.