04-Network Connectivity

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25-MLD snooping configuration
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Contents

Configuring MLD snooping· 1

About MLD snooping· 1

Fundamentals of MLD snooping· 1

MLD snooping ports· 1

How MLD snooping works· 3

Protocols and standards· 4

Restrictions and guidelines: MLD snooping configuration· 4

VLAN-based MLD snooping tasks at a glance· 4

Enabling the MLD snooping feature· 5

Enabling MLD snooping for VLANs· 5

Configuring basic MLD snooping features· 6

Specifying an MLD snooping version· 6

Setting the maximum number of MLD snooping forwarding entries· 7

Configuring static IPv6 multicast MAC address entries· 7

Setting the MLD last listener query interval 8

Configuring MLD snooping port features· 9

Setting aging timers for dynamic ports· 9

Configuring a static member port 10

Configuring a static router port 10

Configuring a port as a simulated member host 10

Enabling fast-leave processing· 11

Disabling a port from becoming a dynamic router port 12

Configuring the MLD snooping querier 12

Enabling the MLD snooping querier 12

Configuring parameters for MLD general queries and responses· 13

Configuring parameters for MLD messages· 14

Configuring source IPv6 addresses for MLD messages· 14

Setting the 802.1p priority for MLD messages· 14

Configuring MLD snooping policies· 15

Configuring an IPv6 multicast group policy· 15

Enabling dropping unknown IPv6 multicast data· 16

Enabling MLD report suppression· 16

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

Enabling IPv6 multicast group replacement 17

Display and maintenance commands for MLD snooping· 18

MLD snooping configuration examples· 19

Example: Configuring MLD snooping on a wireless network· 19

Troubleshooting MLD snooping· 21

Layer 2 multicast forwarding cannot function· 21

IPv6 multicast group policy does not work· 22

 


Configuring MLD snooping

About MLD snooping

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 Layer 3 device.

Fundamentals of MLD snooping

As shown in Figure 1, when MLD snooping is not enabled, the Layer 2 switch floods IPv6 multicast packets 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 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 devices are called router ports. In Figure 2, Port A1 of Switch A and Port B1 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, 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 another MLD general query before the timer expires, the timer is reset. If the port does not receive another MLD general query or IPv6 PIM hello message 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, Port A2 and Port A3 of Switch A and Port B2 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 a static member port" and "Configuring a static router port."

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

General query

The MLD querier periodically sends MLD general queries to all hosts and devices 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.

 

 

NOTE:

A Layer 2 device does not forward an MLD report through a non-router port because of the host MLD report suppression mechanism. If a non-router port has member host attached, the member hosts suppress their MLD reports upon receiving MLD reports forwarded by the non-router port. The Layer 2 device cannot know the existence of the member hosts attached to the non-router port.

 

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 router ports and member ports of the group in the VLAN. 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

Restrictions and guidelines: MLD snooping configuration

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.

To configure MLD snooping features for VLANs, you must enable MLD snooping for the specific VLANs even though MLD snooping is enabled globally.

Some features can be configured for a VLAN in VLAN view or for multiple VLANs in MLD-snooping view. The VLAN-specific configuration and the configuration made in MLD-snooping view have the same priority, and the most recent configuration takes effect.

Some features can be configured for a VLAN in VLAN view or globally for all VLANs in MLD-snooping view. The VLAN-specific configuration takes priority over the global configuration.

Some features can be configured for an interface in interface view or for all interfaces of the specified VLANs in MLD-snooping view. The interface-specific configuration takes priority over the configuration made in MLD-snooping view.

VLAN-based MLD snooping tasks at a glance

To configure MLD snooping for VLANs, perform the following tasks:

1.     Enabling the MLD snooping feature

2.     Enabling MLD snooping for VLANs

3.     (Optional.) Configuring basic MLD snooping features

¡     Specifying an MLD snooping version

¡     Setting the maximum number of MLD snooping forwarding entries

¡     Configuring static IPv6 multicast MAC address entries

¡     Setting the MLD last listener query interval

4.     (Optional.) Configuring MLD snooping port features

¡     Setting aging timers for dynamic ports

¡     Configuring a static member port

¡     Configuring a static router port

¡     Configuring a port as a simulated member host

¡     Enabling fast-leave processing

¡     Disabling a port from becoming a dynamic router port

5.     (Optional.) Configuring the MLD snooping querier

¡     Enabling the MLD snooping querier

¡     Configuring parameters for MLD general queries and responses

6.     (Optional.) Configuring parameters for MLD messages

¡     Configuring source IPv6 addresses for MLD messages

¡     Setting the 802.1p priority for MLD messages

7.     (Optional.) Configuring MLD snooping policies

¡     Configuring an IPv6 multicast group policy

¡     Enabling dropping unknown IPv6 multicast data

¡     Enabling MLD report suppression

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

¡     Enabling IPv6 multicast group replacement

Enabling the MLD snooping feature

About this task

You must enable the MLD snooping feature before you configure other MLD snooping features.

Procedure

1.     Enter system view.

system-view

2.     Enable the MLD snooping feature and enter MLD-snooping view.

mld-snooping

By default, the MLD snooping feature is disabled.

Enabling MLD snooping for VLANs

Restrictions and guidelines

You can enable MLD snooping for multiple VLANs by using the enable vlan command in MLD-snooping view or for a VLAN by using the mld-snooping enable command in VLAN view. The configuration in VLAN view has the same priority as the configuration in MLD-snooping view.

MLD snooping configuration in a VLAN takes effect only on the member ports in the VLAN.

Enabling MLD snooping for multiple VLANs

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Enable MLD snooping for multiple VLANs.

enable vlan vlan-list

By default, MLD snooping is disabled in a VLAN.

Enabling MLD snooping for a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Enable MLD snooping for the VLAN.

mld-snooping enable

By default, MLD snooping is disabled in a VLAN.

Configuring basic MLD snooping features

Specifying an MLD snooping version

About this task

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

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

·     MLDv2 snooping can process MLDv1 and MLDv2 messages.

Restrictions and guidelines

If you change the version of MLD snooping from 2 to 1, the system performs the following actions:

·     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 a static member port."

Specifying an MLD snooping version for multiple VLANs

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Specify an MLD snooping version for multiple VLANs.

version version-number vlan vlan-list

By default, the MLD snooping version for a VLAN is 1.

Specifying an MLD snooping version for a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Specify an MLD snooping version for the VLAN.

mld-snooping version version-number

By default, the MLD snooping version for a VLAN is 1.

Setting the maximum number of MLD snooping forwarding entries

About this task

You can modify the maximum number of MLD 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, remove some entries manually.

Procedure

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Set the maximum number of MLD snooping forwarding entries.

entry-limit limit

By default, the maximum number of MLD snooping forwarding entries is 4294967295.

Configuring static IPv6 multicast MAC address entries

About this task

In Layer 2 IPv6 multicast, IPv6 multicast MAC address entries can be dynamically created through Layer 2 multicast protocols (such as MLD snooping). You can also manually configure static IPv6 multicast MAC address entries by binding IPv6 multicast MAC addresses and ports to control the destination ports of the IPv6 multicast data.

Restrictions and guidelines

You must specify an unused multicast MAC address when configuring a static IPv6 multicast MAC address entry. A multicast MAC address is the MAC address in which the least significant bit of the most significant octet is 1.

Configuring a static IPv6 multicast MAC address entry in system view

1.     Enter system view.

system-view

2.     Configure a static IPv6 multicast MAC address entry.

mac-address multicast mac-address interface interface-list vlan vlan-id

Configuring a static IPv6 multicast MAC address entry in interface view

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

3.     Configure a static IPv6 multicast MAC address entry.

mac-address multicast mac-address vlan vlan-id

Setting the MLD last listener query interval

About this task

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.

Setting the MLD last listener query interval globally

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Set the MLD last listener query interval globally.

last-listener-query-interval interval

By default, the MLD last listener query interval is 1 second.

Setting the MLD last listener query interval for a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Set the MLD last listener query interval for the VLAN

mld-snooping last-listener-query-interval interval

By default, the MLD last listener query interval is 1 second for a VLAN.

Configuring MLD snooping port features

Setting aging timers for dynamic ports

About this task

A dynamic router port is removed from the dynamic router port list if it does not receive an MLD general query when its aging timer expires.

A dynamic member port is removed from the dynamic member port if it does not receive an MLD report when its aging timer expires.

Restrictions and guidelines

Set an appropriate value for the aging timers of dynamic ports based on the actual network requirement. For example, if the memberships of IPv6 multicast groups frequently change, set a relatively small value for the aging timer of the dynamic member ports.

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."

Setting the aging timers for dynamic ports globally

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Set the aging timer for dynamic router ports globally.

router-aging-time seconds

By default, the aging timer for dynamic router ports is 260 seconds.

4.     Set the aging timer for dynamic member ports globally.

host-aging-time seconds

By default, the aging timer for dynamic member ports is 260 seconds.

Setting the aging timers for dynamic ports in a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Set the aging timer for dynamic router ports in the VLAN.

mld-snooping router-aging-time seconds

By default, the aging timer for dynamic router ports is 260 seconds for a VLAN.

4.     Set the aging timer for dynamic member ports in the VLAN.

mld-snooping host-aging-time seconds

By default, the aging timer for dynamic member ports is 260 seconds for a VLAN.

Configuring a static member port

About this task

You can configure a port as a static member port for an IPv6 multicast group so that all hosts attached to the port can always 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.

Procedure

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

3.     Configure the port as a static member port.

mld-snooping static-group ipv6-group-address [ source-ip ipv6-source-address ] vlan vlan-id

By default, a port is not a static member port.

Configuring a static router port

About this task

You can configure a port as a static router port for an IPv6 multicast group so that all IPv6 multicast data for the group received on the port will be forwarded.

Procedure

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

3.     Configure the port as a static router port.

mld-snooping static-router-port vlan vlan-id

By default, a port is not a static router port.

Configuring a port as a simulated member host

About this task

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 ways as a dynamic member port.

Procedure

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

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

About this task

This feature enables the Layer 2 device to immediately remove a port from the forwarding entry for an IPv6 multicast group when the port receives a done message. The device no longer sends or forwards MLD multicast-address-specific queries for the group to the port.

Restrictions and guidelines

Do not enable fast-leave processing on a port that has multiple receiver hosts attached in a VLAN. If you do so, the remaining receivers cannot receive IPv6 multicast data for a group after a receiver leaves the group.

Enabling fast-leave processing globally

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Enable fast-leave processing globally.

fast-leave [ vlan vlan-list ]

By default, fast-leave processing is disabled globally.

Enabling fast-leave processing on a port

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

3.     Enable fast-leave processing on the port.

mld-snooping fast-leave [ vlan vlan-list ]

By default, fast-leave processing is disabled on a port.

Disabling a port from becoming a dynamic router port

About this task

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

·     All IPv6 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 IPv6 multicast data that it does not expect.

·     The port forwards the MLD general queries to its upstream Layer 3 devices. These messages might affect the multicast routing protocol state (such as the MLD querier or DR election) on the Layer 3 devices. This might further cause network interruption.

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

Restrictions and guidelines

This configuration and the static router port configuration do not interfere with each other.

Procedure

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

3.     Disable the port from becoming a dynamic router port.

mld-snooping router-port-deny [ vlan vlan-list ]

By default, a port is allowed to become a dynamic router port.

Configuring the MLD snooping querier

Enabling the MLD snooping querier

About this task

This feature enables the Layer 2 device 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.

Restrictions and guidelines

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.

Enabling the MLD snooping querier for a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Enable the MLD snooping querier for the VLAN.

mld-snooping querier

By default, the MLD snooping querier is disabled for a VLAN.

Configuring parameters for MLD general queries and responses

About this task

You can modify the MLD general query interval 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.

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.

Restrictions and guidelines

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.

Configuring parameters for MLD general queries and responses globally

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Set the maximum response time for MLD general queries.

max-response-time seconds

By default, the maximum response time for MLD general queries is 10 seconds.

Configuring parameters for MLD general queries and responses for a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Set the MLD general query interval in the VLAN.

mld-snooping query-interval interval

By default, the MLD general query interval for a VLAN is 125 seconds.

4.     Set the maximum response time for MLD general queries in the VLAN.

mld-snooping max-response-time seconds

By default, the maximum response time for MLD general queries for a VLAN is 10 seconds.

Configuring parameters for MLD messages

Configuring source IPv6 addresses for MLD messages

About this task

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.

Configuring the source IPv6 addresses for MLD messages for a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

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 of the VLAN 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

About this task

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

Setting the 802.1p priority for MLD messages globally

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Set the 802.1p priority for MLD messages.

dot1p-priority priority

Setting the 802.1p priority for MLD messages for a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

3.     Set the 802.1p priority for MLD messages in the VLAN.

mld-snooping dot1p-priority priority

Configuring MLD snooping policies

Configuring an IPv6 multicast group policy

About this task

This feature enables the Layer 2 device to filter MLD reports by using an ACL that specifies the IPv6 multicast groups and the optional sources. It is used to control the IPv6 multicast groups that receiver hosts can join. This configuration takes effect on the IPv6 multicast groups that ports join dynamically.

In an IPv6 multicast application, a host sends an unsolicited MLD report when a user requests an IPv6 multicast program. The Layer 2 device uses the IPv6 multicast group policy to filter the MLD report. The host can join the IPv6 multicast group only if the MLD report is permitted by the IPv6 multicast group policy.

Configuring an IPv6 multicast group policy globally

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Configure an IPv6 multicast group policy globally.

group-policy ipv6-acl-number [ vlan vlan-list ]

By default, no IPv6 multicast group policies exist. Hosts can join any IPv6 multicast groups.

Configuring an IPv6 multicast group policy on a port

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

3.     Configure an IPv6 multicast group policy on the port.

mld-snooping group-policy ipv6-acl-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 dropping unknown IPv6 multicast data

About this task

Unknown IPv6 multicast data refers to IPv6 multicast data for which no forwarding entries exist in the MLD snooping forwarding table. This feature enables the device to forward unknown IPv6 multicast data only to the router port. If the device does not have a router port, unknown IPv6 multicast data will be dropped.

If you do not enable this feature, the unknown IPv6 multicast data is flooded in the VLAN to which the data belongs.

Restrictions and guidelines

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

When dropping unknown IPv6 multicast data is enabled, the device also drops unknown IPv4 multicast data.

When dropping unknown IPv6 multicast data is enabled, the device still forwards unknown IPv6 multicast data out of router ports (except the receiving router port).

Enabling dropping unknown IPv6 multicast data globally

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Enable dropping unknown IPv6 multicast data globally.

drop-unknown

By default, this feature is disabled, and unknown IPv6 multicast data is flooded.

Enabling dropping unknown IPv6 multicast data for a VLAN

1.     Enter system view.

system-view

2.     Enter VLAN view.

vlan vlan-id

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.

Enabling MLD report suppression

About this task

This feature enables the Layer 2 device 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. Use this feature to reduce the multicast traffic.

Procedure

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

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

About this task

You can set the maximum number of IPv6 multicast groups on a port to regulate the port traffic. This feature 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. When the number of IPv6 multicast groups on the port reaches the limit, the port automatically drops MLD reports for new IPv6 multicast groups.

Procedure

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

3.     Set the maximum number of IPv6 multicast groups on the port.

mld-snooping group-limit limit [ vlan vlan-list ]

By default, no limit is placed on the maximum number of IPv6 multicast groups on a port.

Enabling IPv6 multicast group replacement

About this task

When IPv6 multicast group replacement is enabled, the port does not drop MLD reports for new groups if the number of multicast groups on the port reaches the upper limit. Instead, the port leaves an IPv6 multicast group that has the lowest IPv6 address and joins the new group contained in the MLD report. The IPv6 multicast group replacement feature is typically used in the channel switching application.

Restrictions and guidelines

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

This feature does not take effect if the following conditions exist:

·     The number of the MLD snooping forwarding entries on the device reaches or exceeds the upper limit.

·     The IPv6 multicast group that the port newly joins is not included in the multicast group list maintained by the device.

Enabling IPv6 multicast group replacement globally

1.     Enter system view.

system-view

2.     Enter MLD-snooping view.

mld-snooping

3.     Enable IPv6 multicast group replacement globally.

overflow-replace [ vlan vlan-list ]

By default, IPv6 multicast group replacement is disabled globally.

Enabling IPv6 multicast group replacement on a port

1.     Enter system view.

system-view

2.     Enter Layer 2 interface view.

¡     Enter Layer 2 Ethernet interface view.

interface interface-type interface-number

¡     Enter Layer 2 aggregate interface view.

interface bridge-aggregation interface-number

3.     Enable IPv6 multicast group replacement on the port.

mld-snooping overflow-replace [ vlan vlan-list ]

By default, IPv6 multicast group replacement is disabled on a port.

Display and maintenance commands for MLD snooping

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

 

Task

Command

Display Layer 2 IPv6 multicast fast forwarding entries.

display ipv6 l2-multicast fast-forwarding cache [ vlan vlan-id ] [ ipv6-source-address | ipv6-group-address ] *

Display information about Layer 2 IPv6 multicast groups.

display ipv6 l2-multicast ip [ group ipv6-group-address | source ipv6-source-address ] * [ vlan vlan-id ]

Display Layer 2 IPv6 multicast group entries.

display ipv6 l2-multicast ip forwarding [ group ipv6-group-address | source ipv6-source-address ] * [ vlan vlan-id ]

Display information about Layer 2 IPv6 MAC multicast groups.

display ipv6 l2-multicast mac [ mac-address ] [ vlan vlan-id ]

Display Layer 2 IPv6 MAC multicast group entries.

display ipv6 l2-multicast mac forwarding [ mac-address ] [ vlan vlan-id ]

Display static IPv6 multicast MAC address entries.

display mac-address [ mac-address [ vlan vlan-id ] | [ multicast ] [ vlan vlan-id ] [ count ] ]

Display MLD snooping status.

display mld-snooping [ global | vlan vlan-id ]

Display dynamic MLD snooping group entries.

display mld-snooping group [ ipv6-group-address | ipv6-source-address ] * [ vlan vlan-id ] [  verbose ]

Display dynamic router port information.

display mld-snooping router-port [ verbose | vlan vlan-id  [ verbose ] ]

Display static MLD snooping group entries.

display mld-snooping static-group [ ipv6-group-address | ipv6-source-address ] * [ vlan vlan-id ] [ verbose ]

Display static router port information.

display mld-snooping static-router-port [ vlan vlan-id ]

Display statistics for the MLD messages learned through MLD snooping.

display mld-snooping statistics

Clear Layer 2 IPv6 multicast fast forwarding entries.

reset ipv6 l2-multicast fast-forwarding cache [ vlan vlan-id ] { { ipv6-source-address | ipv6-group-address } * | all }

Clear dynamic MLD snooping group 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 MLD messages learned through MLD snooping.

reset mld-snooping statistics

 

MLD snooping configuration examples

Example: Configuring MLD snooping on a wireless network

Network configuration

As shown in Figure 3:

·     The source sends IPv6 multicast traffic to IPv6 multicast group FF1E::1.

·     The client is a receiver host of the IPv6 multicast group.

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

Configure the AC so that the client can receive the IPv6 multicast traffic from the source.

Figure 3 Network diagram

 

 

Procedure

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

2.     Configure Router A:

# Enable IPv6 multicast routing.

<RouterA> system-view

[RouterA] ipv6 multicast routing

[RouterA-mrib] quit

[RouterA] interface gigabitethernet 1/0/1

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

[RouterA-GigabitEthernet1/0/1] pim ipv6 dm

[RouterA-GigabitEthernet1/0/1] quit

# Enable MLD on GigabitEthernet 1/0/2.

[RouterA] interface gigabitethernet 1/0/2

[RouterA-GigabitEthernet1/0/2] mld enable

[RouterA-GigabitEthernet1/0/2] quit

3.     Configure WLAN services:

# Create VLAN 100.

<AP> system-view

[AP] Vlan 100

[AP-vlan100] quit

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

[AP] wlan service-template 1

[AP-wlan-st-1] ssid Multicast

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

[AP-wlan-st-1] vlan 100

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

[AP-wlan-st-1] quit

# Bind service template 1 to WLAN radio interface 1/0/1.

[AP] interface WLAN-Radio 1/0/1

[AP-WLAN-Radio1/0/1] service-template 1

[AP-WLAN-Radio1/0/1] quit

4.     Configure MLD snooping:

# Enable the MLD snooping feature.

[AP] mld-snooping

[AP-mld-snooping] quit

# Enable MLD snooping for VLAN 100.

[AP] vlan 100

[AP-vlan100] mld-snooping enable

[AP-vlan100] quit

5.     Configure GigabitEthernet 1/0/1 on the AP as a trunk port, and assign the port to VLAN 100.

[AP] interface gigabitethernet 1/0/1

[AP-GigabitEthernet1/0/1] port link-type trunk

[AP-GigabitEthernet1/0/1] port trunk permit vlan 100

[AP-GigabitEthernet1/0/1] quit

6.     Configure the client to access the WLAN service with the SSID Multicast and request multicast traffic for IPv6 multicast group FF1E::1. (Details not shown.)

Verifying the configuration

# Display detailed information about dynamic MLD snooping group entries for VLAN 100 on the AP.

[AP]display mld-snooping group vlan 100 verbose

Total 1 entries.

 

VLAN 100: Total 1 entries.

  (::,FF1E::101)

    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 AP has joined the IPv6 multicast group FF1E::1.

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 the MLD snooping feature. 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 IPv6 multicast data for 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 interface view to verify that the correct IPv6 multicast group policy has been applied. If the applied 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 it is not, use the drop-unknown or mld-snooping drop-unknown command to enable dropping unknown IPv6 multicast data.

4.     If the problem persists, contact H3C Support.