By analyzing received MLD messages, a Layer 2 device running MLD snooping establishes mappings between ports and multicast MAC addresses and forwards IPv6 multicast data based on these mappings.

As shown in Figure 1, when MLD snooping is not running, IPv6 multicast packets are broadcast to all devices at Layer 2. When MLD snooping runs, multicast packets for known IPv6 multicast groups are multicast to the receivers at Layer 2.

Figure 1 Before and after MLD snooping is enabled on the Layer 2 device

MLD snooping forwards multicast data to only the receivers requiring it at Layer 2. It brings the following advantages:

· Reducing Layer 2 broadcast packets, thus saving network bandwidth

· Enhancing the security of multicast traffic

· Facilitating the implementation of per-host accounting

Basic concepts in MLD snooping

MLD snooping related ports

As shown in Figure 2, Router A connects to the multicast source, MLD snooping runs on Switch A and Switch B, Host A and Host C are receiver hosts (namely, IPv6 multicast group members).

Figure 2 MLD snooping related ports

Ports involved in MLD snooping, as shown in Figure 2, are described as follows:

· Router port—A router port is a port on the Ethernet switch that leads switch toward the Layer-3 multicast device (DR or MLD querier). In the figure, GigabitEthernet 3/0/1 of Switch A and GigabitEthernet 3/0/1 of Switch B are router ports. The switch registers all its local router ports in its router port list.

· Member port—A member port (also known as IPv6 multicast group member port) is a port on the Ethernet switch that leads toward multicast group members. In the figure, GigabitEthernet 3/0/2 and GigabitEthernet 3/0/3 of Switch A and GigabitEthernet 3/0/2 of Switch B are member ports. The switch registers all the member ports on the local device in its MLD snooping forwarding table.

NOTE:

· In this document, a router port is a router-connecting port on the switch, rather than a port on a router.

· Unless otherwise specified, router/member ports mentioned in this document include static and dynamic ports.

· On an MLD snooping-enabled switch, the ports that received MLD general queries with the source address other than 0::0 or IPv6 PIM hello messages are dynamic router ports. For more information about IPv6 PIM hello messages, see the chapter “Configuring IPv6 PIM.”

Aging timers for dynamic ports in MLD snooping

Table 1 Aging timers for dynamic ports in MLD snooping and related messages and actions

Timer	Description	Message before expiry	Action after expiry
Dynamic router port aging timer	For each dynamic router port, the switch sets a timer initialized to the dynamic router port aging time.	MLD general query of which the source address is not 0::0 or IPv6 PIM hello.	The switch removes this port from its router port list.
Dynamic member port aging timer	When a port dynamically joins an IPv6 multicast group, the switch sets a timer for the port, which is initialized to the dynamic member port aging time.	MLD report message.	The switch removes this port from the MLD snooping forwarding table.

NOTE:

The port aging mechanism of MLD snooping works only for dynamic ports; a static port will never age out.

How MLD snooping works

A switch running MLD snooping performs different actions when it receives different MLD messages, as follows:

CAUTION:

The description about adding or deleting a port in this section is only for a dynamic port. Static ports can be added or deleted only through the corresponding configurations. For more information, see “Configuring static ports.”

General queries

The MLD querier periodically sends MLD general queries to all hosts and routers (FF02::1) on the local subnet to find out whether IPv6 multicast group members exist on the subnet.

After receiving an MLD general query, the switch forwards it through all ports in the VLAN except the port on which it received the MLD query and performs the following:

· If the port on which it the switch received the MLD query is a dynamic router port in its router port list, the switch resets the aging timer for this dynamic router port.

· If the port is not included in its router port list, the switch adds it into its router port list as a dynamic router port and sets an aging timer for it.

Membership reports

A host sends an MLD report to the MLD querier in the following circumstances:

· After receiving an MLD query, an IPv6 multicast group member host responds with an MLD report.

· When intended to join an IPv6 multicast group, a host sends an MLD report to the MLD querier to announce that it is interested in the multicast information addressed to that IPv6 multicast group.

After receiving an MLD report, the switch forwards it through all the router ports in the VLAN, resolves the address of the reported IPv6 multicast group, and performs the following to the receiving port:

· If no forwarding table entry exists for the reported IPv6 multicast group, the switch creates an entry, adds the port as a dynamic member port to the outgoing port list, and starts a member port aging timer for that port.

· If a forwarding table entry exists for the reported IPv6 multicast group, but the port is not included in the outgoing port list for that group, the switch adds the port as a dynamic member port to the outgoing port list, and starts a member port aging timer for that port.

· If a forwarding table entry exists for the reported IPv6 multicast group and the port is included in the outgoing port list, which means that this port is already a dynamic member port, the switch resets the member port aging timer for that port.

NOTE:

· A switch does not forward an MLD report through a non-router port. This is because if the switch forwards a report message through a member port, all the attached hosts listening to the reported IPv6 multicast address will suppress their own reports after receiving this report according to the MLD report suppression mechanism for hosts, and this will prevent the switch from knowing whether the reported multicast group still has active members attached to that port.

· For more information about the MLD report suppression mechanism of hosts, see the chapter “Configuring MLD.”

Done messages

When a host leaves an IPv6 multicast group, the host sends an MLD done message to the multicast router.

When the switch receives an MLD done message on a dynamic member port, the switch first checks whether a forwarding table entry for the IPv6 multicast group address in the message exists, and, if one exists, whether the outgoing port list contains the port.

· If the forwarding table entry does not exist or if the outgoing port list does not contain the port, the switch discards the MLD done message instead of forwarding it to any port.

· If the forwarding table entry exists and the outgoing port list contains the port, the switch forwards the MLD done message to all router ports in the native VLAN. Because the switch does not know whether any other hosts attached to the port are still listening to that IPv6 multicast group address, the switch does not immediately remove the port from the outgoing port list of the forwarding table entry for that group. Instead, it resets the aging timer for the port.

After receiving an MLD done message from a host, the MLD querier resolves the IPv6 multicast group address in the message and sends an MLD multicast-address-specific query to that IPv6 multicast group address through the port that received the MLD done message. After receiving the MLD multicast-address-specific query, the switch forwards it through all the router ports in the VLAN and all member ports for that IPv6 multicast group, and performs the following to the receiving port:

· If any MLD report in response to the MLD multicast-address-specific query is received on the port (suppose it is a dynamic member port) before its aging timer expires, this means that some host attached to the port is receiving or expecting to receive IPv6 multicast data for that IPv6 multicast group. The switch resets the aging timer for the port.

· If no MLD report in response to the MLD multicast-address-specific query is received on the port before its aging timer expires, this means that no hosts attached to the port are still listening to that IPv6 multicast group address. The switch removes the port from the outgoing port list of the forwarding table entry for that IPv6 multicast group when the aging timer expires.

MLD snooping proxying

You can configure the MLD snooping proxying function on an edge device to reduce the number of MLD reports and done messages sent to its upstream device. The device configured with MLD snooping proxying is called an MLD snooping proxy. It is a host from the perspective of its upstream device.

NOTE:

Even though an MLD snooping proxy is a host from the perspective of its upstream device, the MLD membership report suppression mechanism for hosts does not take effect on it. For more information about the MLD report suppression mechanism for hosts, see the chapter “Configuring MLD.”

Figure 3 Network diagram for MLD snooping proxying

As shown in Figure 3, Switch A works as an MLD snooping proxy. As a host from the perspective of the querier Router A, Switch A represents its attached hosts to send their membership reports and done messages to Router A.

Table 2 describes how an MLD snooping proxy processes MLD messages.

Table 2 MLD message processing on an MLD snooping proxy

MLD message	Actions
General query	When receiving an MLD general query, the proxy forwards it to all ports but the receiving port. In addition, the proxy generates a report according to the group memberships it maintains and sends the report out all router ports.
Multicast-address-specific query	In response to the MLD group-specific query for a certain IPv6 multicast group, the proxy sends the report to the group out all router ports if the forwarding entry for the group still contains a member port.
Report	When receiving a report for an IPv6 multicast group, the proxy looks up the multicast forwarding table for the entry for the multicast group. If the forwarding entry is found with the receiving port contained as a dynamic port in the outgoing port list, the proxy resets the aging timer for the entry. If the forwarding entry is found but the outgoing port list does not include the receiving port, the proxy adds the port to the outgoing port list as a dynamic member port and starts an aging timer for it. If no forwarding entry is found, the proxy creates the entry, adds the receiving port to the outgoing port list as a dynamic member port and starts an aging timer for the port, and then, sends a report to the group out all router ports.
Done	In response to a done message for an IPv6 multicast group, the proxy sends a multicast-address-specific query for the group out the receiving port. After making sure that no member port is contained in the forwarding entry for the IPv6 multicast group, the proxy sends a done message for the group out all router ports.

Protocols and standards

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

MLD snooping configuration task list

Complete these tasks to configure MLD snooping:

Task		Remarks
Configuring basic MLD snooping functions	Enabling MLD snooping	N/A
	Configuring the version of MLD snooping	Optional
	Configuring limit on the number of forwarding entries globally	Optional
Configuring MLD snooping port functions	Configuring aging timers for dynamic ports	Optional
	Configuring static ports	Optional
	Configuring simulated joining	Optional
	Configuring fast-leave processing	Optional
	Disabling a port from becoming a dynamic router port	Optional
Configuring MLD snooping querier	Enabling MLD snooping querier	Optional
	Configuring MLD queries and responses	Optional
	Configuring source IPv6 addresses of MLD queries	Optional
Configuring MLD snooping proxying	Enabling MLD snooping proxying	Optional
Configuring MLD snooping proxying	Configuring a source IPv6 address for the MLD messages sent by the proxy	Optional
Configuring an MLD snooping policy	Configuring an IPv6 multicast group filter	Optional
	Configuring dropping unknown IPv6 multicast data	Optional
	Configuring MLD report suppression	Optional
	Setting the maximum number of multicast groups that a port can join	Optional
	Configuring IPv6 multicast group replacement	Optional
	Enabling the MLD snooping host tracking function	Optional

NOTE:

· In MLD-snooping view, the configuration is effective for all VLANs. In VLAN view, the configuration is effective on only the ports that belong to the current VLAN. For a given VLAN, the configuration in MLD-snooping view is not effective if the same configuration is made in VLAN view.

· In MLD-snooping view, the configuration is effective on all ports. In Layer 2 Ethernet interface view or Layer 2 aggregate interface view, the configuration is effective on only the current port. In port group view, the configuration is effective on all ports in only the current port group. For a given port, the configuration in MLD-snooping view is not effective if the same configuration is made in Layer 2 Ethernet interface view, Layer 2 aggregate interface view or port group view.

· For MLD snooping, the configuration on a Layer 2 aggregate interface do not interfere with that the configuration on its member ports, nor do they take part in aggregation calculations. The configuration on a member port of the aggregate group will not take effect until it leaves the aggregate group.

Configuring basic MLD snooping functions

Configuration prerequisites

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

· Enable IPv6 forwarding

· Configure the corresponding VLANs

· Determine the version of MLD snooping

Enabling MLD snooping

To enable MLD snooping:

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

NOTE:

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

· After you enable MLD snooping in a VLAN, do not enable MLD or IPv6 PIM on the corresponding VLAN interface, and vice versa.

· When you enable MLD snooping in a specified VLAN, MLD snooping takes effect on the ports in this VLAN only.

Configuring the version of MLD snooping

By configuring the MLD snooping version, you actually configure the version of MLD messages that MLD snooping can process.

· MLDv1 snooping can process MLDv1 messages, but cannot process MLDv2 messages. MLDv2 messages are flooded in the VLAN.

· MLDv2 snooping can process MLDv1 and MLDv2 messages.

To configure the version of MLD snooping:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Configure the version of MLD snooping.	mld-snooping version version-number	Version 1 by default

CAUTION:

If you change MLDv2 snooping to MLDv1 snooping, the system clears all MLD snooping forwarding entries that the system adds dynamically, and also does the following:

· 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 joining, see “Configuring static ports.”

Configuring limit on the number of forwarding entries globally

You can configure the maximum number of entries in the MLD snooping forwarding table. When the number of forwarding entries maintained by the device reaches the threshold, the device creates no more forwarding entries until the some entries time out or get manually removed.

To configure the maximum number of entries in the forwarding table:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter MLD-snooping view.	mld-snooping	N/A
3. Configure the maximum number of MLD snooping entries.	entry-limit limit	2000 by default

NOTE:

If the number of existing entries is larger than the limit when you configure it, the device informs you to remove excessive entries. In this case, the device does not automatically remove any existing entries or create new entries.

Configuring MLD snooping port functions

Configuration prerequisites

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

· Enable MLD snooping in the VLAN

· Configure the corresponding port groups

· Determine the aging time of dynamic router ports

· Determine the aging time of dynamic member ports

· Determine the IPv6 multicast group and IPv6 multicast source addresses

Configuring aging timers for dynamic ports

If the switch receives no MLD general queries or IPv6 PIM hello messages on a dynamic router port, the switch removes the port from the router port list when the aging timer of the port expires.

If the switch receives no MLD reports for an IPv6 multicast group on a dynamic member port, the switch removes the port from the outgoing port list of the forwarding table entry for that IPv6 multicast group when the port aging timer expires.

If IPv6 multicast group memberships change frequently, you can set a relatively small value for the dynamic member port aging timer.

Configuring aging timers for dynamic ports globally

To configure 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. Configure dynamic router port aging time.	router-aging-time interval	260 seconds by default
4. Configure dynamic member port aging time.	host-aging-time interval	260 seconds by default

Configuring aging timers for dynamic ports in a VLAN

To configure 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. Configure dynamic router port aging time.	mld-snooping router-aging-time interval	260 seconds by default
4. Configure dynamic member port aging time.	mld-snooping host-aging-time interval	260 seconds by default

Configuring static ports

If all the hosts attached to a port is interested in the IPv6 multicast data addressed to a particular IPv6 multicast group, you can configure that port as a static member port for that IPv6 multicast group.

You can configure a port of a switch to be a static router port, through which the switch can forward all IPv6 multicast data it received.

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, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Configure the port or ports as static member port or ports.	mld-snooping static-group ipv6-group-address [ source-ip ipv6-source-address ] vlan vlan-id	No static member ports by default.
4. Configure the port or ports as static router port or ports.	mld-snooping static-router-port vlan vlan-id	No static router ports by default.

NOTE:

· A static member port does not respond to queries from the MLD querier; when you configure a port as a static member port or cancel this configuration on the port, the port does not send an unsolicited MLD report or an MLD done message.

· Static member ports and static router ports never age out. To remove such a port, you need to use the corresponding undo command.

Configuring simulated joining

Generally, a host running MLD responds to MLD queries from the MLD querier. If a host fails to respond due to some reasons, the multicast router will deem that no member of this IPv6 multicast group exists on the network segment, and therefore will remove the corresponding forwarding path.

To avoid this situation from happening, you can enable simulated joining on a port of the switch. Namely, you can configure the port as a simulated member host for an IPv6 multicast group. When an MLD query is received, simulated host gives a response. Thus, the switch can continue receiving IPv6 multicast data.

A simulated host acts like a real host, as follows:

· When a port is configured as a simulated member host, the switch sends an unsolicited MLD report through that port.

· After a port is configured as a simulated member host, the switch responds to MLD general queries by sending MLD reports through that port.

· When the simulated joining function is disabled on a port, the switch sends an MLD done message through that port.

To configure simulated joining:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Configure simulated joining.	mld-snooping host-join ipv6-group-address [ source-ip ipv6-source-address ] vlan vlan-id	Disabled by default

NOTE:

· Each simulated host is equivalent to an independent host. For example, when receiving an MLD query, the simulated host corresponding to each configuration responds respectively.

· Unlike a static member port, a port configured as a simulated member host will age out like a dynamic member port.

Configuring fast-leave processing

The fast-leave processing feature allows the switch to process MLD done messages in a fast way. With the fast-leave processing feature enabled, when receiving an MLD done message on a port, the switch immediately removes that port from the outgoing port list of the forwarding table entry for the indicated IPv6 multicast group. Then, when receiving MLD done multicast-address-specific queries for that IPv6 multicast group, the switch will not forward them to that port.

In VLANs where only one host is attached to each port, fast-leave processing helps improve bandwidth and resource usage. However, if fast-leave processing is enabled on a port to which more than one host is attached, when one host leaves a multicast group, the other hosts attached to the port and interested in the same multicast group will fail to receive multicast data for that group. Therefore, if the function of dropping unknown IPv6 multicast traffic is already enabled on the switch or in the VLANs, the fast-leave processing function should not be enabled.

Configuring fast-leave processing globally

To configure 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.	fast-leave [ vlan vlan-list ]	Disabled by default

Configuring fast-leave processing on a port or a group of ports

To configure fast-leave processing on a port or a group of 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, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Enable fast-leave processing.	mld-snooping fast-leave [ vlan vlan-list ]	Disabled by default

Disabling a port from becoming a dynamic router port

The following problems exist in a multicast access network:

· After receiving an MLD general query or IPv6 PIM hello message from a connected host, a router port becomes a dynamic router port. Before its timer expires, this dynamic router port will receive all multicast packets within the VLAN it belongs to and forward then to the host, thus affecting normal multicast reception of the host.

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

To solve these problems, you can disable the router port from becoming a dynamic router port after receiving an MLD general query or IPv6 PIM hello message, so as to enhance network security and the control over multicast users.

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, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
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.

NOTE:

This configuration does not affect the static router port configuration.

Configuring MLD snooping querier

Configuration prerequisites

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

· Enable MLD snooping in the VLAN

· Determine the MLD general query interval

· Determine the MLD last-member query interval

· Determine the maximum response time for MLD general queries

· Determine the source IPv6 address of MLD general queries

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

Enabling MLD snooping querier

In an IPv6 multicast network running MLD, a multicast router or Layer 3 multicast switch is responsible for sending periodic MLD general queries, so that all Layer 3 multicast devices can establish and maintain multicast forwarding entries, thus to forward multicast traffic correctly at the network layer. This router or Layer 3 switch is called MLD querier.

However, a Layer 2 multicast switch does not support MLD, and therefore cannot send MLD general queries by default. By enabling MLD snooping querier on a Layer 2 switch in a VLAN where multicast traffic needs to be Layer-2 switched only and no Layer 3 multicast devices are present, the Layer 2 switch will act as the MLD querier to send periodic MLD queries, thus allowing multicast forwarding entries to be established and maintained at the data link layer.

To enable the MLD snooping querier:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Enable the MLD snooping querier.	mld-snooping querier	Disabled by default

CAUTION:

It is meaningless to configure an MLD snooping querier in an IPv6 multicast network running MLD. Although an MLD snooping querier does not take part in MLD querier elections, it might affect MLD querier elections because it sends MLD general queries with a low source IPv6 address. For more information about MLD querier, see the chapter “Configuring MLD.”

Configuring MLD queries and responses

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

A multicast listening host starts a timer for each IPv6 multicast group that it has joined when it receives an MLD query (general query or multicast-address-specific query). This timer is initialized to a random value in the range of 0 to the maximum response time advertised in the MLD query message. When the timer value decreases to 0, the host sends an MLD report to the IPv6 multicast group.

To speed up the response of hosts to MLD queries and avoid simultaneous timer expirations causing MLD report traffic bursts, you must properly set the maximum response time.

· For MLD general queries, the maximum response time is set by the max-response-time command.

· For MLD multicast-address-specific queries, the maximum response time equals the last listener query interval.

Configuring MLD queries and responses globally

To configure MLD 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. Configure the maximum response time for MLD general queries.	max-response-time interval	10 seconds by default
4. Configure the MLD last-member query interval.	last-listener-query-interval interval	1 second by default

Configuring MLD queries and responses in a VLAN

To configure MLD 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. Configure MLD query interval.	mld-snooping query-interval interval	125 seconds by default
4. Configure the maximum response time for MLD general queries.	mld-snooping max-response-time interval	10 seconds by default
5. Configure the MLD last-member query interval.	mld-snooping last-listener-query-interval interval	1 second by default

CAUTION:

Make sure that the MLD query interval is greater than the maximum response time for MLD general queries. Otherwise undesired deletion of IPv6 multicast members might occur.

Configuring source IPv6 addresses of MLD queries

This configuration allows you to change the source IPv6 address of MLD queries.

To configure source IPv6 addresses of MLD queries:

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 of MLD general queries.	mld-snooping general-query source-ip { ipv6-address \| current-interface }	FE80::02FF:FFFF:FE00:0001 by default
4. Configure the source IPv6 address of MLD multicast-address-specific queries.	mld-snooping special-query source-ip { ipv6-address \| current-interface }	FE80::02FF:FFFF:FE00:0001 by default

CAUTION:

The source IPv6 address of MLD query messages might affect MLD querier election within the segment.

Configuring MLD snooping proxying

Configuration prerequisites

Before you configure MLD snooping proxying in a VLAN, complete the following tasks:

· Enable MLD snooping in the VLAN

· Determine the source IPv6 address for the MLD reports sent by the proxy

· Determine the source IPv6 address for the MLD done messages sent by the proxy

Enabling MLD snooping proxying

The MLD snooping proxying function works on a per-VLAN basis. After you enable the function in a VLAN, the device works as the MLD snooping proxy for the downstream hosts and upstream router in the VLAN.

To enable MLD snooping proxying 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 MLD snooping proxying in the VLAN.	mld-snooping proxying enable	Disabled by default

Configuring a source IPv6 address for the MLD messages sent by the proxy

You can set the source IPv6 addresses in the MLD reports and done messages sent by the MLD snooping proxy on behalf of its attached hosts.

To configure the source IPv6 addresses for the MLD messages sent by the MLD snooping proxy on behalf of its attached hosts 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 a source IPv6 address for the MLD reports sent by the proxy.	mld-snooping report source-ip { ipv6-address \| current-interface }	The default is FE80::02FF:FFFF:FE00:0001.
4. Configure a source IPv6 address for the MLD done messages sent by the proxy.	mld-snooping done source-ip { ipv6-address \| current-interface }	The default is FE80::02FF:FFFF:FE00:0001.

Configuring an MLD snooping policy

Configuration prerequisites

Before you configure an MLD snooping policy, complete the following tasks:

· Enable MLD snooping in the VLAN

· Determine the IPv6 ACL rule for IPv6 multicast group filtering

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

Configuring an IPv6 multicast group filter

On a MLD snooping–enabled switch, the configuration of an IPv6 multicast group filter allows the service provider to define limits of multicast programs available to different users.

In an actual application, when a user requests a multicast program, the user’s host initiates an MLD report. After receiving this report message, the switch checks the report against the configured ACL rule. If the port on which the report was received can join this IPv6 multicast group, the switch adds an entry for this port in the MLD snooping forwarding table. Otherwise the switch drops this report message. Any IPv6 multicast data that fails the ACL check will not be sent to this port. In this way, the service provider can control the VOD programs provided for multicast users.

Configuring an IPv6 multicast group filter globally

To configure an IPv6 multicast group 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 filter.	group-policy acl6-number [ vlan vlan-list ]	By default, no IPv6 group filter is globally configured. That is, hosts in VLANs can join any valid multicast group.

Configuring an IPv6 multicast group filter on a port or a group of ports

To configure an IPv6 multicast group filer on a port or a group of 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, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Configure an IPv6 multicast group filter.	mld-snooping group-policy acl6-number [ vlan vlan-list ]	By default, no IPv6 group filter is configured on an interface. That is, hosts on the interface can join any valid multicast group.

Configuring dropping 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. After the switch receives such IPv6 multicast traffic, it performs the following operation:

· With the function of dropping unknown IPv6 multicast data enabled, the switch drops all unknown IPv6 multicast data received.

· With the function of dropping unknown IPv6 multicast data disabled, the switch floods unknown IPv6 multicast data in the VLAN to which the unknown IPv6 multicast data belongs.

To enable 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.	mld-snooping drop-unknown	Disabled by default

NOTE:

After enabled to drop unknown IPv6 multicast data, the switch still forward unknown IPv6 multicast data to other router ports in the VLAN.

Configuring MLD report suppression

When a Layer 2 device receives an MLD report from an IPv6 multicast group member, the Layer 2 device forwards the message to the Layer 3 device directly connected with it. Thus, when multiple members belonging to an IPv6 multicast group exist on the Layer 2 device, the Layer 3 device directly connected with it will receive duplicate MLD reports from these members.

With the MLD report suppression function enabled, within a query interval, the Layer 2 device forwards only the first MLD report of an IPv6 group to the Layer 3 device and will not forward the subsequent MLD reports from the same multicast group to the Layer 3 device. This helps reduce the number of packets being transmitted over the network.

To configure 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	Enabled by default

CAUTION:

On an MLD snooping proxy, MLD membership reports are suppressed if the entries for the corresponding groups exist in the forwarding table, no matter the suppression function is enabled or not.

Setting the maximum number of multicast groups that a port can join

By configuring the maximum number of IPv6 multicast groups that a port can join, you can limit the number of multicast programs available to VOD users, thus to control the traffic on the port.

Follow these steps configure the maximum number of IPv6 multicast groups that a port can join:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Configure the maximum number of IPv6 multicast groups that a port can join.	mld-snooping group-limit limit [ vlan vlan-list ]	1024 by default

NOTE:

When you configure this maximum number, if the number of IPv6 multicast groups the port has joined exceeds the configured maximum value, the system deletes all the forwarding entries for the port from the MLD snooping forwarding table, and the hosts on this port join IPv6 multicast groups again until the number of IPv6 multicast groups that the port joins reaches the maximum value. When the port joins an IPv6 multicast group, if the port has been configured as a static member port, the system applies the configurations to the port again. If you have configured simulated joining on the port, the system establishes corresponding forwarding entry for the port after receiving a report from the simulated member host.

Configuring IPv6 multicast group replacement

For some special reasons, the number of IPv6 multicast groups that a switch or a port can join might exceed the upper limit. In some specific applications, an IPv6 multicast group that the switch newly joins must replace an existing IPv6 multicast group. A typical example is “channel switching”: To view a new TV channel, a user switches from the current IPv6 multicast group to the new one.

To address this situation, you can enable the IPv6 multicast group replacement function on the switch or a certain port. When the number of IPv6 multicast groups that the switch or the port has joined exceeds the limit, one of the following occurs:

· If IPv6 multicast group replacement is not enabled, new MLD reports are automatically discarded.

· If IPv6 multicast group replacement is enabled, the IPv6 multicast group that the switch or the port newly joins automatically replaces an existing IPv6 multicast group that has the lowest IPv6 address.

Configuring IPv6 multicast group replacement globally

To configure 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.	overflow-replace [ vlan vlan-list ]	Disabled by default

Configuring IPv6 multicast group replacement on a port or a group of ports

To configure IPv6 multicast group replacement on a port or a group of 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, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Enable IPv6 multicast group replacement.	mld-snooping overflow-replace [ vlan vlan-list ]	Disabled by default.

CAUTION:

Be sure to configure the maximum number of IPv6 multicast groups that a port can join to a value other than the default one (see “Setting the maximum number of multicast groups that a port can join”) before enabling IPv6 multicast group replacement. Otherwise, the IPv6 multicast group replacement function does not take effect.

Enabling the MLD snooping host tracking function

With the MLD snooping host tracking function, the switch can record the information of the member hosts that are receiving IPv6 multicast traffic, including the host IPv6 address, running duration, and timeout time. You can monitor and manage the member hosts according to the recorded information.

Enabling the MLD snooping host tracking function globally

To enable the MLD snooping host tracking function globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter MLD-snooping view.	mld-snooping	N/A
3. Enable the MLD snooping host tracking function globally.	host-tracking	Disabled by default

Enabling the MLD snooping host tracking function in a VLAN

To enable the MLD snooping host tracking function 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 the MLD snooping host tracking function in the VLAN.	mld-snooping host-tracking	Disabled by default

Displaying and maintaining MLD snooping

Task	Command	Remarks
Display MLD snooping group information (in standalone mode).	display mld-snooping group [ vlan vlan-id ] [ slot slot-number ] [ verbose ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Display MLD snooping group information (in IRF mode).	display mld-snooping group [ vlan vlan-id ] [ chassis chassis-number slot slot-number ] [ verbose ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Display information about the hosts tracked by MLD snooping (in standalone mode).	display mld-snooping host vlan vlan-id group ipv6-group-address [ source ipv6-source-address ] [ slot slot-number ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Display information about the hosts tracked by MLD snooping (in IRF mode).	display mld-snooping host vlan vlan-id group ipv6-group-address [ source ipv6-source-address ] [ chassis chassis-number slot slot-number ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Display the statistics for MLD messages learned through MLD snooping.	display mld-snooping statistics [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Remove dynamic group entries of a specified MLD snooping group or all MLD snooping groups.	reset mld-snooping group { ipv6-group-address \| all } [ vlan vlan-id ]	Available in user view
Clear the statistics for all MLD messages learned through MLD snooping.	reset mld-snooping statistics	Available in user view

MLD snooping configuration examples

NOTE:

By default, Ethernet interfaces, VLAN interfaces, and aggregate interfaces are in the state of DOWN. To configure such an interface, use the undo shutdown command to bring it up first.

IPv6 group policy and simulated joining configuration example

Network requirements

As shown in Figure 4, Router A connects to the IPv6 multicast source through GigabitEthernet 3/1/2 and to Switch A through GigabitEthernet 3/1/1. MLDv1 runs on Router A, MLDv1 snooping required on Switch A, and Router A acts as the MLD querier on the subnet. The receivers, Host A and Host B can receive IPv6 multicast traffic addressed to IPv6 multicast group FF1E::101 only.

IPv6 multicast data for group FF1E::101 can be forwarded through GigabitEthernet 3/0/3 and GigabitEthernet 3/0/4 of Switch A even if Host A and Host B accidentally, temporarily stop receiving IPv6 multicast data. Switch A drops unknown IPv6 multicast data and does not broadcast the data to the VLAN where Switch A resides.

Figure 4 Network diagram

Configuration procedure

1. Enable IPv6 forwarding and configure IPv6 addresses:

Enable IPv6 forwarding and configure an IPv6 address and prefix length for each interface as per Figure 4. (Details not shown)

2. Configure Router A:

# Enable IPv6 multicast routing, enable IPv6 PIM-DM on each interface, and enable MLDv1 on GigabitEthernet 3/1/1.

<RouterA> system-view

[RouterA] multicast ipv6 routing-enable

[RouterA] interface GigabitEthernet 3/1/1

[RouterA-GigabitEthernet3/1/1] mld enable

[RouterA-GigabitEthernet3/1/1] pim ipv6 dm

[RouterA-GigabitEthernet3/1/1] quit

[RouterA] interface Gigabitethernet 3/1/2

[RouterA-GigabitEthernet3/1/2] pim ipv6 dm

[RouterA-GigabitEthernet3/1/2] quit

3. Configure Switch A:

# Enable MLD snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

# Create VLAN 100, assign GigabitEthernet 3/0/1 through GigabitEthernet 3/0/4 to this VLAN, and enable MLD snooping and the function of dropping IPv6 unknown multicast traffic in the VLAN.

[SwitchA] vlan 100

[SwitchA-vlan100] port GigabitEthernet 3/0/1 to GigabitEthernet 3/0/4

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] mld-snooping drop-unknown

[SwitchA-vlan100] quit

# Configure an IPv6 multicast group filter so that the hosts in VLAN 100 can join only the 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 3/0/3 and GigabitEthernet 3/0/4 as simulated hosts for IPv6 multicast group FF1E::101.

[SwitchA] interface GigabitEthernet 3/0/3

[SwitchA-GigabitEthernet3/0/3] mld-snooping host-join ff1e::101 vlan 100

[SwitchA-GigabitEthernet3/0/3] quit

[SwitchA] interface GigabitEthernet 3/0/4

[SwitchA-GigabitEthernet3/0/4] mld-snooping host-join ff1e::101 vlan 100

[SwitchA-GigabitEthernet3/0/4] quit

4. Verify the configuration:

# Display the detailed MLD snooping group information in VLAN 100 on Switch A.

[SwitchA] display mld-snooping group vlan 100

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Port flags: D-Dynamic port, S-Static port, C-Copy port, P-PIM port

Subvlan flags: R-Real VLAN, C-Copy VLAN

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Router port(s):total 1 port(s).

GE3/0/1 (D)

IP group(s):the following ip group(s) match to one mac group.

IP group address:FF1E::101

(::, FF1E::101):

Attribute: Host Port

Host port(s):total 2 port(s).

GE3/0/3 (D)

GE3/0/4 (D)

MAC group(s):

MAC group address:3333-0000-0101

Host port(s):total 2 port(s).

GE3/0/3

GE3/0/4

The output shows that GigabitEthernet 3/0/3 and GigabitEthernet 3/0/4 of Switch A have joined IPv6 multicast group FF1E::101.

Static port configuration example

Network requirements

As shown in Figure 5, Router A connects to an IPv6 multicast source (Source) through GigabitEthernet 3/1/2, and to Switch A through GigabitEthernet 3/1/1. MLDv1 runs on Router A, and MLDv1 snooping runs on Switch A, Switch B and Switch C. Router A acts as the MLD querier.

Host A and host C are permanent receivers of IPv6 multicast group FF1E::101. GigabitEthernet 3/0/3 and GigabitEthernet 3/0/5 on Switch C are required to be configured as static member ports for multicast group FF1E::101 to enhance the reliability of multicast traffic transmission.

Suppose Spanning Tree Protocol (STP) runs on the network. To avoid data loops, the forwarding path from Switch A to Switch C is blocked under normal conditions, and IPv6 multicast traffic flows to the receivers attached to Switch C only along the path of Switch A—Switch B—Switch C. Configure GigabitEthernet 3/0/3 on Switch C as a static router port, so that IPv6 multicast traffic can flow to the receivers nearly uninterruptedly along the path of Switch A—Switch C in the case that the path of Switch A—Switch B—Switch C gets blocked.

NOTE:

· If no static router port is configured, when the path of Switch A—Switch B—Switch C gets blocked, at least one MLD query-response cycle must be completed before the IPv6 multicast data can flow to the receivers along the new path of Switch A—Switch C. Namely, IPv6 multicast delivery will be interrupted during this process.

· For more information about STP, see Layer 2—LAN Switching Configuration Guide.

Figure 5 Network diagram

Configuration procedure

1. Enable IPv6 forwarding and configure IPv6 addresses:

Enable IPv6 forwarding and configure an IPv6 address and prefix length for each interface as per Figure 5.

2. Configure Router A:

# Enable IPv6 multicast routing, enable IPv6 PIM-DM on each interface, and enable MLD on GigabitEthernet 3/1/1.

<RouterA> system-view

[RouterA] multicast ipv6 routing-enable

[RouterA] interface GigabitEthernet 3/1/1

[RouterA-GigabitEthernet3/1/1] mld enable

[RouterA-GigabitEthernet3/1/1] pim ipv6 dm

[RouterA-GigabitEthernet3/1/1] quit

[RouterA] interface Gigabitethernet 3/1/2

[RouterA-GigabitEthernet3/1/2] pim ipv6 dm

[RouterA-GigabitEthernet3/1/2] quit

3. Configure Switch A:

# Enable MLD snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

# Create VLAN 100, assign GigabitEthernet 3/0/1 through GigabitEthernet 3/0/3 to this VLAN, and enable MLD snooping in the VLAN.

[SwitchA] vlan 100

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

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] quit

# Configure GigabitEthernet 3/0/3 to be a static router port.

[SwitchA] interface GigabitEthernet 3/0/3

[SwitchA-GigabitEthernet3/0/3] mld-snooping static-router-port vlan 100

[SwitchA-GigabitEthernet3/0/3] quit

4. Configure Switch B:

# Enable MLD snooping globally.

<SwitchB> system-view

[SwitchB] mld-snooping

[SwitchB-mld-snooping] quit

# Create VLAN 100, assign GigabitEthernet 3/0/1 and GigabitEthernet 3/0/2 to this VLAN, and enable MLD snooping in the VLAN.

[SwitchB] vlan 100

[SwitchB-vlan100] port GigabitEthernet 3/0/1 GigabitEthernet 3/0/2

[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, assign GigabitEthernet 3/0/1 through GigabitEthernet 3/0/5 to this VLAN, and enable MLD snooping in the VLAN.

[SwitchC] vlan 100

[SwitchC-vlan100] port GigabitEthernet 3/0/1 to GigabitEthernet 3/0/5

[SwitchC-vlan100] mld-snooping enable

[SwitchC-vlan100] quit

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

[SwitchC] interface GigabitEthernet 3/0/3

[SwitchC-GigabitEthernet3/0/3] mld-snooping static-group ff1e::101 vlan 100

[SwitchC-GigabitEthernet3/0/3] quit

[SwitchC] interface GigabitEthernet 3/0/5

[SwitchC-GigabitEthernet3/0/5] mld-snooping static-group ff1e::101 vlan 100

[SwitchC-GigabitEthernet3/0/5] quit

6. Verify the configuration:

# Display the detailed MLD snooping group information in VLAN 100 on Switch A.

[SwitchA] display mld-snooping group vlan 100 verbose

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Port flags: D-Dynamic port, S-Static port, C-Copy port, P-PIM port

Subvlan flags: R-Real VLAN, C-Copy VLAN

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Router port(s):total 2 port(s).

GE3/0/1 (D)

GE3/0/3 (S)

IP group(s):the following ip group(s) match to one mac group.

IP group address:FF1E::101

(::, FF1E::101):

Attribute: Host Port

Host port(s):total 1 port(s).

GE3/0/2 (D)

MAC group(s):

MAC group address:3333-0000-0101

Host port(s):total 1 port(s).

GE3/0/2

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

# Display the detailed MLD snooping group information in VLAN 100 on Switch C.

[SwitchC] display mld-snooping group vlan 100 verbose

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Port flags: D-Dynamic port, S-Static port, C-Copy port, P-PIM port

Subvlan flags: R-Real VLAN, C-Copy VLAN

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Router port(s):total 1 port(s).

GE3/0/2 (D)

IP group(s):the following ip group(s) match to one mac group.

IP group address:FF1E::101

(::, FF1E::101):

Attribute: Host Port

Host port(s):total 2 port(s).

GE3/0/3 (S)

GE3/0/5 (S)

MAC group(s):

MAC group address:3333-0000-0101

Host port(s):total 2 port(s).

GE3/0/3

GE3/0/5

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

MLD snooping querier configuration example

Network requirements

As shown in Figure 6, in a Layer-2-only network environment, two multicast sources Source 1 and Source 2 send IPv6 multicast data to multicast groups FF1E::101 and FF1E::102 respectively, Host A and Host C are receivers of multicast group FF1E::101, and Host B and Host D are receivers of multicast group FF1E::102. MLDv1 runs on all the receivers and MLDv1 snooping runs on all the switches. Switch A, which is close to the multicast sources, is chosen as the MLD snooping querier.

To prevent flooding of IPv6 unknown multicast traffic within the VLAN, be sure to configure all the switches to drop IPv6 unknown multicast data packets.

Figure 6 Network diagram

Configuration procedure

1. Configure Switch A:

# Enable IPv6 forwarding and enable MLD snooping globally.

<SwitchA> system-view

[SwitchA] ipv6

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

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

[SwitchA] vlan 100

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

# Enable MLD snooping and the function of dropping unknown IPv6 multicast data packets in VLAN 100.

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] mld-snooping drop-unknown

# Configure MLD snooping querier feature in VLAN 100.

[SwitchA-vlan100] mld-snooping querier

[SwitchA-vlan100] quit

2. Configure Switch B:

# Enable IPv6 forwarding and enable MLD snooping globally.

<SwitchB> system-view

[SwitchB] ipv6

[SwitchB] mld-snooping

[SwitchB-mld-snooping] quit

# Create VLAN 100, add GigabitEthernet 3/0/1 through GigabitEthernet 3/0/4 into VLAN 100.

[SwitchB] vlan 100

[SwitchB-vlan100] port GigabitEthernet 3/0/1 to GigabitEthernet 3/0/4

# Enable the MLD snooping feature and the function of dropping unknown IPv6 multicast data packets in VLAN 100.

[SwitchB-vlan100] mld-snooping enable

[SwitchB-vlan100] mld-snooping drop-unknown

[SwitchB-vlan100] quit

Configurations of Switch C and Switch D are similar to the configuration of Switch B.

3. Verify the configuration:

When the MLD snooping querier starts to work, all the switches but the querier receive MLD general queries.

# Display the MLD message statistics on Switch B.

[SwitchB-vlan100] 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.

MLD snooping proxying configuration example

Network requirements

As shown in Figure 7, Router A connects to an IPv6 multicast source through port GigabitEthernet 3/1/2, and to Switch A through port GigabitEthernet 3/1/1. MLDv1 runs on Router A and MLDv1 snooping runs on Switch A. Router A acts as the MLD querier.

Configure MLD snooping proxying on Switch A, enabling the switch to forward MLD reports and done messages on behalf of attached hosts and to respond to MLD queries from Router A and forward the queries to the hosts on behalf of Router A.

Figure 7 Network diagram

Configuration procedure

1. Configure IPv6 addresses for interfaces:

Configure an IP address and prefix length for each interface as per Figure 7. (Details not shown)

2. Configure Router A:

# Enable IPv6 multicast routing, enable IPv6 PIM-DM on each interface, and enable MLD on port GigabitEthernet 3/1/1.

<RouterA> system-view

[RouterA] multicast ipv6 routing-enable

[RouterA] interface Gigabitethernet 3/1/1

[RouterA-GigabitEthernet3/1/1] mld enable

[RouterA-GigabitEthernet3/1/1] pim ipv6 dm

[RouterA-GigabitEthernet3/1/1] quit

[RouterA] interface Gigabitethernet 3/1/2

[RouterA-GigabitEthernet3/1/2] pim ipv6 dm

[RouterA-GigabitEthernet3/1/2] quit

3. Configure Switch A:

# Enable MLD snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

# Create VLAN 100, assign ports GigabitEthernet 3/0/1 through GigabitEthernet 3/0/4 to this VLAN, and enable MLD snooping and MLD snooping proxying in the VLAN.

[SwitchA] vlan 100

[SwitchA-vlan100] port Gigabitethernet 3/0/1 to Gigabitethernet 3/0/4

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] mld-snooping proxying enable

[SwitchA-vlan100] quit

4. Verify the configuration:

After the configuration is completed, Host A and Host B send MLD join messages addressed to group FF1E::101. When receiving the messages, Switch A sends a join message for the group out port GigabitEthernet 3/0/1 (a router port) to Router A. Use the display mld-snooping group command and the display mld group command to display information about MLD snooping groups and MLD multicast groups. For example:

# Display information about MLD snooping groups on Switch A.

[SwitchA] display mld-snooping group

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Port flags: D-Dynamic port, S-Static port, C-Copy port, P-PIM port

Subvlan flags: R-Real VLAN, C-Copy VLAN

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Router port(s):total 1 port(s).

GE3/0/1 (D)

IP group(s):the following ip group(s) match to one mac group.

IP group address:FF1E::101

(::, FF1E::101):

Host port(s):total 2 port(s).

GE3/0/3 (D)

GE3/0/4 (D)

MAC group(s):

MAC group address:3333-0000-0101

Host port(s):total 2 port(s).

GE3/0/3

GE3/0/4

# Display information about MLD multicast groups on Router A.

[RouterA] display mld group

Total 1 MLD Group(s).

Interface group report information

GigabitEthernet3/1/1(2001::1):

Total 1 MLD Group reported

Group Address: FF1E::1

Last Reporter: FE80::2FF:FFFF:FE00:1

Uptime: 00:00:03

Expires: 00:04:17

When Host A leaves the IPv6 multicast group, it sends an MLD done message to Switch A. Receiving the message, Switch A removes port GigabitEthernet 3/0/3 from the member port list of the forwarding entry for the group; however, it does not remove the group or forward the done message to Router A because Host B is still in the group. Use the display mld-snooping group command to display information about MLD snooping groups. For example:

# Display information about MLD snooping groups on Switch A.

[SwitchA] display mld-snooping group

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Port flags: D-Dynamic port, S-Static port, C-Copy port, P-PIM port

Subvlan flags: R-Real VLAN, C-Copy VLAN

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

Router port(s):total 1 port(s).

GE3/0/1 (D)

IP group(s):the following ip group(s) match to one mac group.

IP group address:FF1E::101

(::, FF1E::101):

Host port(s):total 1 port(s).

GE3/0/4 (D)

MAC group(s):

MAC group address:3333-0000-0101

Host port(s):total 1 port(s).

GE3/0/4

Troubleshooting MLD snooping

Layer 2 multicast forwarding cannot work

Symptom

Layer 2 multicast forwarding cannot work.

Analysis

MLD snooping is not enabled.

Solution

1. Use display current-configuration command to view the running status of MLD snooping.

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

3. If MLD snooping is disabled only for the corresponding VLAN, use the mld-snooping enable command in VLAN view to enable MLD snooping in the corresponding VLAN.

Configured IPv6 multicast group policy fails to take effect

Symptom

Although an IPv6 multicast group policy has been configured to allow hosts to join specific IPv6 multicast groups, the hosts can still receive IPv6 multicast data addressed to other groups.

Analysis

· The IPv6 ACL rule is incorrectly configured.

· The IPv6 multicast group policy is not correctly applied.

· The function of dropping unknown IPv6 multicast data is not enabled, so unknown IPv6 multicast data is flooded.

Solution

1. Use the display acl ipv6 command to check the configured IPv6 ACL rule. Make sure that the IPv6 ACL rule conforms to the IPv6 multicast group policy to be implemented.

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

3. Use the display current-configuration command to check whether the function of dropping unknown IPv6 multicast data is enabled. If not, use the drop-unknown or mld-snooping drop-unknown command to enable the function of dropping unknown IPv6 multicast data.

Appendix

Processing of IPv6 multicast protocol messages

With Layer 3 multicast routing enabled, an MLD snooping–enabled switch processes IPv6 multicast protocol messages differently under different conditions, as follows:

· If only MLD is enabled on the switch, or if both MLD and IPv6 PIM are enabled on the switch, the switch does the following:

¡ Maintains dynamic member ports or dynamic router ports according to MLD packets

¡ Maintains dynamic router ports according to IPv6 PIM hello packets

· If only IPv6 PIM is enabled on the switch, the following occurs:

¡ The switch broadcasts MLD messages as unknown messages in the VLAN.

¡ After receiving an IPv6 PIM hello message, the switch maintains the corresponding dynamic router port.

· If MLD is disabled on the switch, one of the following occurs:

¡ If IPv6 PIM is disabled, the switch deletes all its dynamic member ports and dynamic router ports.

¡ If IPv6 PIM is enabled, the switch deletes only its dynamic member ports but not its dynamic router ports.

NOTE:

On a switch with Layer 3 IPv6 multicast routing enabled, use the display mld group port-info command to display Layer 2 port information. For more information about this command, see IP Multicast Command Reference.

· If IPv6 PIM is disabled on the switch, one of the following occurs:

¡ If MLD is disabled, the switch deletes all its dynamic router ports.

¡ If MLD is enabled, the switch maintains all its dynamic member ports and dynamic router ports.

08-IP Multicast Configuration Guide

MLD snooping related ports

General queries

Membership reports

Done messages

Configuring basic MLD snooping functions

Enabling MLD snooping

Configuring the version of MLD snooping

Configuring limit on the number of forwarding entries globally

Configuring aging timers for dynamic ports

Configuring aging timers for dynamic ports globally

Configuring aging timers for dynamic ports in a VLAN

Configuring simulated joining

Configuring fast-leave processing

Configuring fast-leave processing globally

Configuring fast-leave processing on a port or a group of ports

Configuring MLD snooping querier

Enabling MLD snooping querier

Configuring MLD queries and responses

Configuring MLD queries and responses globally

Configuring MLD queries and responses in a VLAN

Configuring source IPv6 addresses of MLD queries

Configuring an MLD snooping policy

Configuring an IPv6 multicast group filter

Configuring an IPv6 multicast group filter on a port or a group of ports

Configuring dropping unknown IPv6 multicast data

Configuring IPv6 multicast group replacement

Configuring IPv6 multicast group replacement on a port or a group of ports

Enabling the MLD snooping host tracking function

Enabling the MLD snooping host tracking function globally

Enabling the MLD snooping host tracking function in a VLAN

MLD snooping configuration examples

IPv6 group policy and simulated joining configuration example

Network requirements

Configuration procedure

Static port configuration example

Network requirements

Configuration procedure

MLD snooping querier configuration example

Network requirements

Configuration procedure

Network requirements

Configuration procedure

Troubleshooting MLD snooping

Layer 2 multicast forwarding cannot work

Symptom

Analysis

Solution

Symptom

Analysis

Solution

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