This manual chiefly focuses on the IP multicast technology and device operations. Unless otherwise stated, the term “multicast” in this document refers to IP multicast.

1.1 Introduction to Multicast

As a technique coexisting with unicast and broadcast, the multicast technique effectively addresses the issue of point-to-multipoint data transmission. By allowing high-efficiency point-to-multipoint data transmission over a network, multicast greatly saves network bandwidth and reduces network load.

With the multicast technology, a network operator can easily provide new value-added services, such as live Webcasting, Web TV, distance learning, telemedicine, Web radio, real-time videoconferencing, and other bandwidth- and time-critical information services.

1.1.1 Comparison of Information Transmission Techniques

I. Unicast

In unicast, the information source sends a separate copy of information to each host that needs the information, as shown in Figure 1-1.

Figure 1-1 Unicast transmission

Assume that Hosts B, D and E need this information. The information source establishes a separate transmission channel for each of these hosts.

In unicast transmission, the traffic over the network is proportional to the number of hosts that need the information. If a large number of users need the information, the information source needs to send a copy of the same information to each of these users. This means a tremendous pressure on the information source and the network bandwidth.

As we can see from the information transmission process, unicast is not suitable for batch transmission of information.

II. Broadcast

In broadcast, the information source sends information to all hosts on the network, even if some hosts do not need the information, as shown in Figure 1-2.

Figure 1-2 Broadcast transmission

Assume that only Hosts B, D, and E need the information. If the information source broadcasts the information, Hosts A and C also receive it. In addition to information security issues, this also causes traffic flooding on the same network.

Therefore, broadcast is disadvantageous in transmitting data to specific hosts; moreover, broadcast transmission is a significant usage of network resources.

III. Multicast

As discussed above, the unicast and broadcast techniques are unable to provide point-to-multipoint data transmissions with the minimum network consumption.

The multicast technique has solved this problem. When some hosts on the network need multicast information, the multicast source (Source in the figure) sends only one copy of the information. Multicast distribution threes are built for the multicast packets through multicast routing protocols, and the packets are replicated only on nodes where the trees branch, as shown in Figure 1-3:

Figure 1-3 Multicast transmission

Assume that Hosts B, D and E need the information. To receive the information correctly, these hosts need to join a receiver set, which is known as a multicast group. The routers on the network duplicate and forward the information based on the distribution of the receivers in this set. Finally, the information is correctly delivered to Hosts B, D, and E.

To sum up, multicast has the following advantages:

l Over unicast: As multicast traffic flows to the node the farthest possible from the source before it is replicated and distributed, an increase of the number of hosts will not remarkably add to the network load.

l Over broadcast: As multicast data is sent only to the receivers that need it, multicast uses the network bandwidth reasonably and brings no waste of network resources, and enhances network security.

1.1.2 Roles in Multicast

The following roles are involved in multicast transmission:

l An information sender is referred to as a Multicast Source (“Source” in Figure 1-3).

l Each receiver is a Multicast Group Member (“Receiver” in Figure 1-3).

l All receivers interested in the same information form a Multicast Group. Multicast groups are not subject to geographic restrictions.

l A router that supports Layer 3 multicast is called multicast router or Layer 3 multicast device. In addition to providing the multicast routing function, a multicast router can also manage multicast group members.

For a better understanding of the multicast concept, you can assimilate multicast transmission to the transmission of TV programs, as shown in Table 1-1.

Table 1-1 An analogy between TV transmission and multicast transmission

Step	TV transmission	Multicast transmission
1	A TV station transmits a TV program through a channel.	A multicast source sends multicast data to a multicast group.
2	A user tunes the TV set to the channel.	A receiver joins the multicast group.
3	The user starts to watch the TV program transmitted by the TV station via the channel.	The receiver starts to receive the multicast data that the source sends to the multicast group.
4	The user turns off the TV set or tunes to another channel.	The receiver leaves the multicast group or joins another group.

& Note:

l A multicast source does not necessarily belong to a multicast group. Namely, a multicast source is not necessarily a multicast data receiver.

l A multicast source can send data to multiple multicast groups at the same time, and multiple multicast sources can send data to the same multicast group at the same time.

1.1.3 Advantages and Applications of Multicast

I. Advantages of multicast

Advantages of the multicast technique include:

l Enhanced efficiency: reduces the CPU load of information source servers and network devices.

l Optimal performance: reduces redundant traffic.

l Distributive application: Enables point-to-multiple-point applications at the price of the minimum network resources.

II. Applications of multicast

Applications of the multicast technique include:

l Multimedia and streaming applications, such as Web TV, Web radio, and real-time video/audio conferencing.

l Communication for training and cooperative operations, such as distance learning and telemedicine.

l Data warehouse and financial applications (stock quotes).

l Any other point-to-multiple-point data distribution application.

1.2 Multicast Models

Based on how the receivers treat the multicast sources, there are two multicast models:

I. ASM model

In the ASM model, any sender can send information to a multicast group as a multicast source, and numbers of receivers can join a multicast group identified by a group address and obtain multicast information addressed to that multicast group. In this model, receivers are not aware of the position of multicast sources in advance. However, they can join or leave the multicast group at any time.

II. SSM model

In the practical life, users may be interested in the multicast data from only certain multicast sources. The SSM model provides a transmission service that allows users to specify the multicast sources they are interested in at the client side.

The radical difference between the SSM model and the ASM model is that in the SSM model, receivers already know the locations of the multicast sources by some other means. In addition, the SSM model uses a multicast address range that is different from that of the ASM model, and dedicated multicast forwarding paths are established between receivers and the specified multicast sources.

1.3 Multicast Architecture

IP multicast addresses the following questions:

l Where should the multicast source transmit information to? (multicast addressing)

l What receivers exist on the network? (host registration)

l Where is the multicast source from which the receivers need to receive multicast data? (multicast source discovery)

l How should information be transmitted to the receivers? (multicast routing)

IP multicast falls in the scope of end-to-end service. The multicast architecture involves the following four parts:

1) Addressing mechanism: Information is sent from a multicast source to a group of receivers through a multicast address.

2) Host registration: Receiver hosts are allowed to join and leave multicast groups dynamically. This mechanism is the basis for group membership management.

3) Multicast routing: A multicast distribution tree (namely a forwarding path tree for multicast data on the network) is constructed for delivering multicast data from a multicast source to receivers.

4) Multicast applications: A software system that supports multicast applications, such as video conferencing, must be installed on multicast sources and receiver hosts, and the TCP/IP stack must support reception and transmission of multicast data.

1.3.1 Multicast Addresses

To allow communication between multicast sources and multicast group members, network-layer multicast addresses, namely, multicast IP addresses must be provided. In addition, a technique must be available to map multicast IP addresses to link-layer multicast MAC addresses.

I. IPv4 multicast addresses

Internet Assigned Numbers Authority (IANA) assigned the Class D address space (224.0.0.0 to 239.255.255.255) for IPv4 multicast. The specific address blocks and usages are shown in Table 1-2.

Table 1-2 Class D IP address blocks and description

Address block	Description
224.0.0.0 to 224.0.0.255	Reserved permanent group addresses. The IP address 224.0.0.0 is reserved, and other IP addresses can be used by routing protocols and for topology searching, protocol maintenance, and so on. Commonly used permanent group addresses are listed in Table 1-3. A packet destined for an address in this block will not be forwarded beyond the local subnet regardless of the Time to Live (TTL) value in the IP header.
224.0.1.0 to 238.255.255.255	Globally scoped group addresses. This block includes two types of designated group addresses: l 232.0.0.0/8: SSM group addresses, and l 233.0.0.0/8: Glop group addresses; for details, see RFC 2770.
239.0.0.0 to 239.255.255.255	Administratively scoped multicast addresses. These addresses are considered to be locally rather than globally unique, and can be reused in domains administered by different organizations without causing conflicts. For details, refer to RFC 2365.

& Note:

l The membership of a group is dynamic. Hosts can join or leave multicast groups at any time.

l “Glop” is a mechanism for assigning multicast addresses between different autonomous systems (ASs). By filling an AS number into the middle two bytes of 233.0.0.0, you get 255 multicast addresses for that AS.

Table 1-3 Some reserved multicast addresses

Address	Description
224.0.0.1	All systems on this subnet, including hosts and routers
224.0.0.2	All multicast routers on this subnet
224.0.0.3	Unassigned
224.0.0.4	Distance Vector Multicast Routing Protocol (DVMRP) routers
224.0.0.5	Open Shortest Path First (OSPF) routers
224.0.0.6	OSPF designated routers/backup designated routers
224.0.0.7	Shared Tree (ST) routers
224.0.0.8	ST hosts
224.0.0.9	Routing Information Protocol version 2 (RIPv2) routers
224.0.0.11	Mobile agents
224.0.0.12	Dynamic Host Configuration Protocol (DHCP) server/relay agent
224.0.0.13	All Protocol Independent Multicast (PIM) routers
224.0.0.14	Resource Reservation Protocol (RSVP) encapsulation
224.0.0.15	All Core-Based Tree (CBT) routers
224.0.0.16	Designated Subnetwork Bandwidth Management (SBM)
224.0.0.17	All SBMs
224.0.0.18	Virtual Router Redundancy Protocol (VRRP)

II. IPv6 Multicast Addresses

As defined in RFC 4291, the format of an IPv6 multicast is as follows:

Figure 1-4 IPv6 multicast format

l 0xFF: 8 bits, indicating that this address is an IPv6 multicast address.

l Flags: 4 bits, of which the high-order flag is reserved and set to 0; the definition and usage of the second bit can be found in RFC 3956; and definition and usage of the third bit can be found in RFC 3306; the low-order bit is the Transient (T) flag. When set to 0, the T flag indicates a permanently-assigned multicast address assigned by IANA; when set to 1, the T flag indicates a transient, or dynamically assigned multicast address.

l Scope: 4 bits, indicating the scope of the IPv6 internetwork for which the multicast traffic is intended. Possible values of this field are given in Table 1-4.

l Reserved: 80 bits, all set to 0 currently.

l Group ID: 112 bits, identifying the multicast group. For details about this field, refer to RFC 3306.

Table 1-4 Values of the Scope field

Value	Meaning
0, 3, F	Reserved
1	Node-local scope
2	Link-local scope
4	Admin-local scope
5	Site-local scope
6, 7, 9 through D	Unassigned
8	Organization-local scope
E	Global scope

III. Ethernet multicast MAC addresses

When a unicast IP packet is transmitted over Ethernet, the destination MAC address is the MAC address of the receiver. When a multicast packet is transmitted over Ethernet, however, the destination address is a multicast MAC address because the packet is directed to a group formed by a number of receivers, rather than to one specific receiver.

1) IPv4 multicast MAC addresses

As defined by IANA, the high-order 24 bits of an IPv4 multicast MAC address are 0x01005e, bit 25 is 0x0, and the low-order 23 bits are the low-order 23 bits of a multicast IPv4 address. The IPv4-to-MAC mapping relation is shown in Figure 1-5.

Figure 1-5 IPv4-to-MAC address mapping

The high-order four bits of a multicast IPv4 address are 1110, indicating that this address is a multicast address, and only 23 bits of the remaining 28 bits are mapped to a MAC address, so five bits of the multicast IPv4 address are lost. As a result, 32 multicast IPv4 addresses map to the same MAC address. Therefore, in Layer 2 multicast forwarding, a device may receive some multicast data addressed for other IPv4 multicast groups, and such redundant data needs to be filtered by the upper layer.

2) IPv6 multicast MAC addresses

The high-order 16 bits of an IPv6 multicast MAC address are 0x3333, and the low-order 32 bits are the low-order 32 bits of a multicast IPv6 address. Figure 1-6 shows an example of mapping an IPv6 multicast address, FF1E::F30E:0101, to a MAC address.

Figure 1-6 An example of IPv6-to-MAC address mapping

1.3.2 Multicast Protocols

& Note:

l Generally, we refer to IP multicast working at the network layer as Layer 3 multicast and the corresponding multicast protocols as Layer 3 multicast protocols, which include IGMP/MLD, PIM/IPv6 PIM, and MSDP; we refer to IP multicast working at the data link layer as Layer 2 multicast and the corresponding multicast protocols as Layer 2 multicast protocols, which include IGMP Snooping/MLD Snooping, and multicast VLAN/IPv6 multicast VLAN.

l IGMP Snooping, IGMP, multicast VLAN, PIM and MSDP are for IPv4, MLD Snooping, MLD, IPv6 multicast VLAN, and IPv6 PIM are for IPv6.

This section provides only general descriptions about applications and functions of the Layer 2 and Layer 3 multicast protocols in a network. For details of these protocols, refer to the respective chapters.

I. Layer 3 multicast protocols

Layer 3 multicast protocols include multicast group management protocols and multicast routing protocols. Figure 1-7 describes where these multicast protocols are in a network.

Figure 1-7 Positions of Layer 3 multicast protocols

1) Multicast management protocols

Typically, the internet group management protocol (IGMP) or multicast listener discovery protocol (MLD) is used between hosts and Layer 3 multicast devices directly connected with the hosts. These protocols define the mechanism of establishing and maintaining group memberships between hosts and Layer 3 multicast devices.

2) Multicast routing protocols

A multicast routing protocol runs on Layer 3 multicast devices to establish and maintain multicast routes and forward multicast packets correctly and efficiently. Multicast routes constitute a loop-free data transmission path from a data source to multiple receivers, namely, a multicast distribution tree.

In the ASM model, multicast routes come in intra-domain routes and inter-domain routes.

l An intra-domain multicast routing protocol is used to discover multicast sources and build multicast distribution trees within an AS so as to deliver multicast data to receivers. Among a variety of mature intra-domain multicast routing protocols, protocol independent multicast (PIM) is a popular one. Based on the forwarding mechanism, PIM comes in two modes – dense mode (often referred to as PIM-DM) and sparse mode (often referred to as PIM-SM).

l An inter-domain multicast routing protocol is used for delivery of multicast information between two ASs. So far, mature solutions include multicast source discovery protocol (MSDP).

For the SSM model, multicast routes are not divided into inter-domain routes and intra-domain routes. Since receivers know the position of the multicast source, channels established through PIM-SM are sufficient for multicast information transport.

II. Layer 2 multicast protocols

Layer 2 multicast protocols include IGMP Snooping/MLD Snooping and multicast VLAN/IPv6 multicast VLAN. Figure 1-8 shows where these protocols are in the network.

Figure 1-8 Position of Layer 2 multicast protocols

1) IGMP Snooping/MLD Snooping

Running on Layer 2 devices, Internet Group Management Protocol Snooping (IGMP Snooping) and Multicast Listener Discovery Snooping (MLD Snooping) are multicast constraining mechanisms that manage and control multicast groups by listening to and analyzing IGMP or MLD messages exchanged between the hosts and Layer 3 multicast devices, thus effectively controlling the flooding of multicast data in a Layer 2 network.

2) Multicast VLAN/IPv6 multicast VLAN

In the traditional multicast-on-demand mode, when users in different VLANs on a Layer 2 device need multicast information, the upstream Layer 3 device needs to forward a separate copy of the multicast data to each VLAN of the Layer 2 device. With the multicast VLAN or IPv6 multicast VLAN feature enabled on the Layer 2 device, the Layer 3 multicast device needs to send only one copy of multicast to the multicast VLAN or IPv6 multicast VLAN on the Layer 2 device. This avoids waste of network bandwidth and extra burden on the Layer 3 device.

1.4 Multicast Packet Forwarding Mechanism

In a multicast model, a multicast source sends information to the host group identified by the multicast group address in the destination address field of IP multicast packets. Therefore, to deliver multicast packets to receivers located in different parts of the network, multicast routers on the forwarding path usually need to forward multicast packets received on one incoming interface to multiple outgoing interfaces. Compared with a unicast model, a multicast model is more complex in the following aspects.

l To ensure multicast packet transmission in the network, unicast routing tables or multicast routing tables specially provided for multicast must be used as guidance for multicast forwarding.

l To process the same multicast information from different peers received on different interfaces of the same device, every multicast packet is subject to a reverse path forwarding (RPF) check on the incoming interface. The result of the RPF check determines whether the packet will be forwarded or discarded. The RPF check mechanism is the basis for most multicast routing protocols to implement multicast forwarding.

Chapter 2 IGMP Snooping Configuration

When configuring IGMP Snooping, go to the following sections for information you are interested in:

l IGMP Snooping Overview

l IGMP Snooping Configuration Task List

l Displaying and Maintaining IGMP Snooping

l IGMP Snooping Configuration Examples

l Troubleshooting IGMP Snooping Configuration

2.1 IGMP Snooping Overview

Internet Group Management Protocol Snooping (IGMP Snooping) is a multicast constraining mechanism that runs on Layer 2 devices to manage and control multicast groups.

2.1.1 Principle of IGMP Snooping

By analyzing received IGMP messages, a Layer 2 device running IGMP Snooping establishes mappings between ports and multicast addresses and forwards multicast data based on these mappings.

As shown in Figure 2-1, when IGMP Snooping is not running on the switch, multicast packets are broadcast to all devices at Layer 2. When IGMP Snooping is running on the switch, multicast packets for known multicast groups are multicast to the receivers, rather than broadcast to all hosts, at Layer 2.

Figure 2-1 Before and after IGMP Snooping is enabled on the Layer 2 device

2.1.2 Basic Concepts in IGMP Snooping

I. IGMP Snooping related ports

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

Figure 2-2 IGMP Snooping related ports

Ports involved in IGMP Snooping, as shown in Figure 2-2, are described as follows:

l Router port: A router port is a port on the Ethernet switch that leads switch towards the Layer 3 multicast device (DR or IGMP querier). In the figure, Ethernet 1/0/1 of Switch A and Ethernet 1/0/1 of Switch B are router ports. The switch registers all its local router ports (including static and dynamic router ports) in its router port list.

l Member port: A member port is a port on the Ethernet switch that leads switch towards multicast group members. In the figure, Ethernet 1/0/2 and Ethernet 1/0/3 of Switch A and Ethernet 1/0/2 of Switch B are member ports. The switch registers all the member ports (including static and dynamic member ports) on the local device in its IGMP Snooping forwarding table.

& Note:

l Whenever mentioned in this document, a router port is a port on the switch that leads the switch to a Layer 3 multicast device, rather than a port on a router.

l An IGMP-snooping-enabled switch deems that all its ports on which IGMP general queries with the source address other than 0.0.0.0 or PIM hello messages are received to be router ports.

II. Aging timers for dynamic ports in IGMP Snooping and related messages and actions

Table 2-1 Aging timers for dynamic ports in IGMP Snooping and related messages and actions

Timer	Description	Message before expiry	Action after expiry
Router port aging timer	For each router port, the switch sets a timer initialized to the aging time of the route port.	IGMP general query of which the source address is not 0.0.0.0 or PIM hello	The switch removes this port from its router port list.
Member port aging timer	When a port joins a multicast group, the switch sets a timer for the port, which is initialized to the member port aging time.	IGMP membership report	The switch removes this port from the multicast group forwarding table.

& Note:

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

2.1.3 Work Mechanism of IGMP Snooping

A switch running IGMP Snooping performs different actions when it receives different IGMP messages, as follows:

I. When receiving a general query

The IGMP querier periodically sends IGMP general queries to all hosts and routers (224.0.0.1) on the local subnet to find out whether active multicast group members exist on the subnet.

Upon receiving an IGMP general query, the switch forwards it through all ports in the VLAN except the receiving port and performs the following to the receiving port:

l If the receiving port is a router port existing in its router port list, the switch resets the aging timer of this router port.

l If the receiving port is not a router port existing in its router port list, the switch adds it into its router port list and sets an aging timer for this router port.

II. When receiving a membership report

A host sends an IGMP report to the multicast router in the following circumstances:

l Upon receiving an IGMP query, a multicast group member host responds with an IGMP report.

l When intended to join a multicast group, a host sends an IGMP report to the multicast router to announce that it is interested in the multicast information addressed to that group.

Upon receiving an IGMP report, the switch forwards it through all the router ports in the VLAN, resolves the address of the reported multicast group, and performs the following:

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

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

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

& Note:

A switch does not forward an IGMP report through a non-router port. The reason is as follows: Due to the IGMP report suppression mechanism, if the switch forwards a report message through a member port, all the attached hosts listening to the reported multicast address will suppress their own reports upon hearing this report, and this will prevent the switch from knowing whether any hosts attached to that port are still active members of the reported multicast group.

III. When receiving a leave group message

When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave group message, so the switch cannot know immediately that the host has left the multicast group. However, as the host stops sending IGMP reports as soon as it leaves a multicast group, the switch deletes the forwarding entry for the member port corresponding to the host from the forwarding table when its aging timer expires.

When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP leave group message to the multicast router.

When the switch hears a group-specific IGMP leave group message on a member port, it first checks whether a forwarding table entry for that group exists, and, if one exists, whether its outgoing port list contains that port.

l If the forwarding table entry does not exist or if its outgoing port list does not contain the port, the switch discards the IGMP leave group message instead of forwarding it to any port.

l If the forwarding table entry exists and its outgoing port list contains the port, the switch forwards the leave group message to all router ports in the VLAN. Because the switch does not know whether any other hosts attached to the port are still listening to that group address, the switch does not immediately removes the port from the outgoing port list of the forwarding table entry for that group; instead, it resets the member port aging timer for the port.

Upon receiving the IGMP leave group message from a host, the IGMP querier resolves from the message the address of the multicast group that the host just left and sends an IGMP group-specific query to that multicast group through the port that received the leave group message. Upon hearing the IGMP group-specific query, the switch forwards it through all its router ports in the VLAN and all member ports for that multicast group, and performs the following:

l If any IGMP report in response to the group-specific query is heard on a member port before its aging timer expires, this means that some host attached to the port is receiving or expecting to receive multicast data for that multicast group. The switch resets the aging timer of the member port.

l If no IGMP report in response to the group-specific query is heard on a member port before its aging timer expires, this means that no hosts attached to the port are still listening to that group address: the switch removes the port from the outgoing port list of the forwarding table entry for that multicast group when the aging timer expires.

2.1.4 Protocols and Standards

IGMP Snooping is documented in:

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

2.2 IGMP Snooping Configuration Task List

Complete these tasks to configure IGMP Snooping:

Task		Remarks
Configuring Basic Functions of IGMP Snooping	Enabling IGMP Snooping	Required
Configuring Basic Functions of IGMP Snooping	Configuring the Version of IGMP Snooping	Optional
Configuring IGMP Snooping Port Functions	Configuring Aging Timers for Dynamic Ports	Optional
	Configuring Static Ports	Optional
	Configuring Simulated Joining	Optional
	Configuring Fast Leave Processing	Optional
Configuring IGMP Snooping Querier	Enabling IGMP Snooping Querier	Optional
	Configuring IGMP Queries and Responses	Optional
	Configuring Source IP Address of IGMP Queries	Optional
Configuring an IGMP Snooping Policy	Configuring a Multicast Group Filter	Optional
	Configuring Multicast Source Port Filtering	Optional
	Configuring the Function of Dropping Unknown Multicast Data	Optional
	Configuring IGMP Report Suppression	Optional
	Configuring Maximum Multicast Groups that Can Be Joined on a Port	Optional
	Configuring Multicast Group Replacement	Optional

& Note:

l Configurations made in IGMP Snooping view are effective for all VLANs, while configurations made in VLAN view are effective only for ports belonging to the current VLAN. For a given VLAN, a configuration made in IGMP Snooping view is effective only if the same configuration is not made in VLAN view.

l Configurations made in IGMP Snooping view are effective for all ports; configurations made in Ethernet port view are effective only for the current port; configurations made in manual port group view are effective only for all the ports in the current port group; configurations made in aggregation group view are effective only for the master port. For a given port, a configuration made in IGMP Snooping view is effective only if the same configuration is not made in Ethernet port view or port group view.

2.3 Configuring Basic Functions of IGMP Snooping

2.3.1 Configuration Prerequisites

Before configuring the basic functions of IGMP Snooping, complete the following task:

l Configure the corresponding VLANs.

Before configuring the basic functions of IGMP Snooping, prepare the following data:

l Version of IGMP Snooping.

2.3.2 Enabling IGMP Snooping

Follow these steps to enable IGMP Snooping:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enable IGMP Snooping globally and enter IGMP-Snooping view	igmp-snooping	Required Disabled by default
Return to system view	quit	—
Enter VLAN view	vlan vlan-id	—
Enable IGMP Snooping in the VLAN	igmp-snooping enable	Required Disabled by default

& Note:

l IGMP Snooping must be enabled globally before it can be enabled in a VLAN.

l When you enable IGMP Snooping in a specified VLAN, this function takes effect for Ethernet ports in this VLAN only.

2.3.3 Configuring the Version of IGMP Snooping

By configuring an IGMP Snooping version, you actually configure the version of IGMP messages that IGMP Snooping can process.

l IGMP Snooping version 2 can process IGMPv1 and IGMPv2 messages, but not IGMPv3 messages, which will be flooded in the VLAN.

l IGMP Snooping version 3 can process IGMPv1, IGMPv2 and IGMPv3 messages.

Follow these steps to configure the version of IGMP Snooping:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Configure the version of IGMP Snooping	igmp-snooping version version-number	Optional Version 2 by default

Caution:

If you switch IGMP Snooping from version 3 to version 2, the system will clear all IGMP Snooping forwarding entries from dynamic joins, and will:

l Keep forwarding entries for version 3 static (*, G) joins;

l Clear forwarding entries from version 3 static (S, G) joins, which will be restored when IGMP Snooping is switched back to version 3.

For details about static joins, Refer to Configuring Static Ports.

2.4 Configuring IGMP Snooping Port Functions

2.4.1 Configuration Prerequisites

Before configuring IGMP Snooping port functions, complete the following tasks:

l Enable IGMP Snooping in the VLAN

l Configure the corresponding port groups.

Before configuring IGMP Snooping port functions, prepare the following data:

l Aging time of router ports,

l Aging timer of member ports, and

l Multicast group and multicast source addresses

2.4.2 Configuring Aging Timers for Dynamic Ports

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

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

I. Configuring aging timers for dynamic ports globally

Follow these steps to configure aging timers for dynamic ports globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IGMP Snooping view	igmp-snooping	—
Configure router port aging time	router-aging-time interval	Optional 105 seconds by default
Configure member port aging time	host-aging-time interval	Optional 260 seconds by default

II. Configuring aging timers for dynamic ports in a VLAN

Follow these steps to configure aging timers for dynamic ports in a VLAN:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Configure router port aging time	igmp-snooping router-aging-time interval	Optional 105 seconds by default
Configure member port aging time	igmp-snooping host-aging-time interval	Optional 260 seconds by default

2.4.3 Configuring Static Ports

If all the hosts attached to a port are interested in the multicast data addressed to a particular multicast group or the multicast data that a particular multicast source sends to a particular group, you can configure static (*, G) or (S, G) joining on that port, namely configure the port as a group-specific or source-and-group-specific static member port.

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

Follow these steps to configure static ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command.
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command.
Configure the port(s) as static member port(s)		igmp-snooping static-group group-address [ source-ip source_address ] vlan vlan-id	Required Disabled by default
Configure the port(s) as static router port(s)		igmp-snooping static-router-port vlan vlan-id	Required Disabled by default

& Note:

l The static (S, G) joining function is available only if a valid multicast source address is specified and IGMP Snooping version 3 is currently running on the switch.

l A static member port does not respond to queries from the IGMP querier; when static (*, G) or (S, G) joining is enabled or disabled on a port, the port does not send an unsolicited IGMP report or an IGMP leave group message.

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

2.4.4 Configuring Simulated Joining

Generally, a host running IGMP responds to IGMP queries from the IGMP querier. If a host fails to respond due to some reasons, the multicast router may deem that no member of this 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 configure the port as a simulated member host for a multicast group. When an IGMP query is heard, the simulated host gives a response. Thus, the switch can continue receiving multicast data.

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

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

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

l When the simulated joining function is disabled on a port, the switch sends an IGMP leave group message through that port.

Follow these steps to configure simulated joining:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure simulated (*, G) or (S, G) joining		igmp-snooping host-join group-address [ source-ip source-address ] vlan vlan-id	Required Disabled by default

& Note:

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

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

2.4.5 Configuring Fast Leave Processing

The fast leave processing feature allows the switch to process IGMP leave group messages in a fast way. With the fast leave processing feature enabled, when receiving an IGMP leave group message on a port, the switch immediately removes that port from the outgoing port list of the forwarding table entry for the indicated group. Then, when receiving IGMP group-specific queries for that 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.

I. Configuring fast leave processing globally

Follow these steps to configure fast leave processing globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IGMP Snooping view	igmp-snooping	—
Enable fast leave processing	fast-leave [ vlan vlan-list ]	Required Disabled by default

II. Configuring fast leave processing on a port or a group of ports

Follow these steps to configure fast leave processing on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Enable fast leave processing		igmp-snooping fast-leave [ vlan vlan-list ]	Required Disabled by default

Caution:

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.

2.5 Configuring IGMP Snooping Querier

2.5.1 Configuration Prerequisites

Before configuring IGMP Snooping querier, complete the following task:

l Enable IGMP Snooping in the VLAN.

Before configuring IGMP Snooping querier, prepare the following data:

l IGMP general query interval,

l IGMP last-member query interval,

l Maximum response time to IGMP general queries,

l Source address of IGMP general queries, and

l Source address of IGMP group-specific queries.

2.5.2 Enabling IGMP Snooping Querier

In an IP multicast network running IGMP, a multicast router or Layer 3 multicast switch is responsible for sending IGMP 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 IGMP querier.

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

Follow these steps to enable IGMP Snooping querier:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Enable IGMP Snooping querier	igmp-snooping querier	Required Disabled by default

Caution:

It is meaningless to configure an IGMP Snooping querier in a multicast network running IGMP. Although an IGMP Snooping querier does not take part in IGMP querier elections, it may affect IGMP querier elections because it sends IGMP general queries with a low source IP address.

2.5.3 Configuring IGMP Queries and Responses

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

Upon receiving an IGMP query (general query or group-specific query), a host starts a timer for each multicast group it has joined. This timer is initialized to a random value in the range of 0 to the maximum response time (the host obtains the value of the maximum response time from the Max Response Time field in the IGMP query it received). When the timer value comes down to 0, the host sends an IGMP report to the corresponding multicast group.

An appropriate setting of the maximum response time for IGMP queries allows hosts to respond to queries quickly and avoids bursts of IGMP traffic on the network caused by reports simultaneously sent by a large number of hosts when the corresponding timers expire simultaneously.

l For IGMP general queries, you can configure the maximum response time to fill their Max Response time field.

l For IGMP group-specific queries, you can configure the IGMP last-member query interval to fill their Max Response time field. Namely, for IGMP group-specific queries, the maximum response time equals to the IGMP last-member query interval.

I. Configuring IGMP queries and responses globally

Follow these steps to configure IGMP queries and responses globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IGMP Snooping view	igmp-snooping	—
Configure the maximum response time to IGMP general queries	max-response-time interval	Optional 10 seconds by default
Configure the IGMP last-member query interval	last-member-query-interval interval	Optional 1 second by default

II. Configuring IGMP queries and responses in a VLAN

Follow these steps to configure IGMP queries and responses in a VLAN:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Configure IGMP general query interval	igmp-snooping query-interval interval	Optional 60 seconds by default
Configure the maximum response time to IGMP general queries	igmp-snooping max-response-time interval	Optional 10 seconds by default
Configure the IGMP last-member query interval	igmp-snooping last-member-query-interval interval	Optional 1 second by default

Caution:

In the configuration, make sure that the IGMP general query interval is larger than the maximum response time for IGMP general queries. Otherwise, multicast group members may be deleted by mistake.

2.5.4 Configuring Source IP Address of IGMP Queries

Upon receiving an IGMP query whose source IP address is 0.0.0.0 on a port, the switch will not set that port as a router port. This may prevent multicast forwarding entries from being correctly created at the data link layer and cause multicast traffic forwarding failure in the end. When a Layer 2 device acts as an IGMP-Snooping querier, to avoid the aforesaid problem, you are commended to configure a non-all-zero IP address as the source IP address of IGMP queries.

Follow these steps to configure source IP address of IGMP queries:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Configure the source address of IGMP general queries	igmp-snooping general-query source-ip { current-interface \| ip-address }	Optional 0.0.0.0 by default
Configure the source IP address of IGMP group-specific queries	igmp-snooping special-query source-ip { current-interface \| ip-address }	Optional 0.0.0.0 by default

Caution:

The source address of IGMP query messages may affect IGMP querier selection within the segment.

2.6 Configuring an IGMP Snooping Policy

2.6.1 Configuration Prerequisites

Before configuring an IGMP Snooping policy, complete the following task:

l Enable IGMP Snooping in the VLAN

Before configuring an IGMP Snooping policy, prepare the following data:

l ACL rule for multicast group filtering

l The maximum number of multicast groups that can pass the ports

2.6.2 Configuring a Multicast Group Filter

On an IGMP Snooping–enabled switch, the configuration of a multicast group allows the service provider to define restrictions on multicast programs available to different users.

In an actual application, when a user requests a multicast program, the user’s host initiates an IGMP report. Upon receiving this report message, the switch checks the report against the configured ACL rule. If the port on which the report was heard can join this multicast group, the switch adds an entry for this port in the IGMP Snooping forwarding table; otherwise the switch drops this report message. Any multicast data that has failed 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.

I. Configuring a multicast group filter globally

Follow these steps to configure a multicast group filter globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IGMP Snooping view	igmp-snooping	—
Configure a multicast group filter	group-policy acl-number [ vlan vlan-list ]	Required No group filter is configured by default, namely hosts can join any multicast group.

II. Configuring a multicast group filter on a port or a group of ports

Follow these steps to configuring a multicast group filter on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure a multicast group filter		igmp-snooping group-policy acl-number [ vlan vlan-list ]	Required No filter is configured by default, namely hosts can join any multicast group.

2.6.3 Configuring Multicast Source Port Filtering

With the multicast source port filtering feature enabled on a port, the port can be connected with multicast receivers only rather than with multicast sources, because the port will block all multicast data packets while it permits multicast protocol packets to pass.

If this feature is disabled on a port, the port can be connected with both multicast sources and multicast receivers.

I. Configuring multicast source port filtering globally

Follow these steps to configure multicast source port filtering globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IGMP Snooping view	igmp-snooping	—
Enable multicast source port filtering	source-deny port interface-list	Required Disabled by default

II. Configuring multicast source port filtering on a port or a group of ports

Follow these steps to configure multicast source port filtering on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Enable multicast source port filtering		igmp-snooping source-deny	Required Disabled by default

& Note:

When enabled to filter IPv4 multicast data based on the source ports, the device is automatically enabled to filter IPv6 multicast data based on the source ports.

2.6.4 Configuring the Function of Dropping Unknown Multicast Data

Unknown multicast data refers to multicast data for which no entries exist in the IGMP Snooping forwarding table. When the switch receives such multicast traffic:

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

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

Follow these steps to configure the function of dropping unknown multicast data in a VLAN:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Enable the function of dropping unknown multicast data	igmp-snooping drop-unknown	Required Disabled by default

& Note:

When enabled to drop unknown IPv4 multicast data, the device is automatically enabled to drop unknown IPv6 multicast data.

2.6.5 Configuring IGMP Report Suppression

When a Layer 2 device receives an IGMP report from a multicast group member, the device forwards the message to the Layer 3 device directly connected with it. Thus, when multiple members of a multicast group are attached to the Layer 2 device, the Layer 3 device directly connected with it will receive duplicate IGMP reports from these members.

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

Follow these steps to configure IGMP report suppression:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IGMP Snooping view	igmp-snooping	—
Enable IGMP report suppression	report-aggregation	Optional Enabled by default

2.6.6 Configuring Maximum Multicast Groups that Can Be Joined on a Port

By configuring the maximum number of multicast groups that can be joined on a port, you can limit the number of multicast programs on-demand available to users, thus to regulate traffic on the port.

Follow these steps to configure the maximum number of multicast groups that can be joined on a port or ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure the maximum number of multicast groups that can be joined on the port(s)		igmp-snooping group-limit limit [ vlan vlan-list ]	Optional The default is 128.

& Note:

l When the number of multicast groups a port has joined reaches the maximum number configured, the system deletes all the forwarding entries persistent to that port from the IGMP Snooping forwarding table, and the hosts on this port need to join the multicast groups again.

l If you have configured static or simulated joins on a port, however, when the number of multicast groups on the port exceeds the configured threshold, the system deletes all the forwarding entries persistent to that port from the IGMP Snooping forwarding table and applies the static or simulated joins again, until the number of multicast groups joined by the port comes back within the configured threshold.

2.6.7 Configuring Multicast Group Replacement

For some special reasons, the number of multicast groups that can be joined on the current switch or port may exceed the number configured for the switch or the port. In addition, in some specific applications, a multicast group newly joined on the switch needs to replace an existing multicast group automatically. A typical example is “channel switching”, namely, by joining a new multicast group, a user automatically switches from the current multicast group to the new one.

To address such situations, you can enable the multicast group replacement function on the switch or certain ports. When the number of multicast groups joined on the switch or a port has joined reaches the limit:

l If the multicast group replacement feature is enabled, the newly joined multicast group automatically replaces an existing multicast group with the lowest address.

l If the multicast group replacement feature is not enabled, new IGMP reports will be automatically discarded.

I. Configuring multicast group replacement globally

Follow these steps to configure multicast group replacement globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter IGMP Snooping view	igmp-snooping	—
Configure multicast group replacement	overflow-replace [ vlan vlan-list ]	Required Disabled by default

II. Configuring multicast group replacement on a port or a group of ports

Follow these steps to configure multicast group replacement on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure multicast group replacement		igmp-snooping overflow-replace [ vlan vlan-list ]	Required Disabled by default

Caution:

Be sure to configure the maximum number of multicast groups allowed on a port (refer to Configuring Maximum Multicast Groups that Can Be Joined on a Port) before configuring multicast group replacement. Otherwise, the multicast group replacement functionality will not take effect.

2.7 Displaying and Maintaining IGMP Snooping

To do...	Use the command...	Remarks
View the information of IGMP Snooping multicast groups	display igmp-snooping group [ vlan vlan-id ] [ verbose ]	Available in any view
View the statistics information of IGMP messages learned by IGMP Snooping	display igmp-snooping statistics	Available in any view
Clear IGMP Snooping multicast group information	reset igmp-snooping group { group-address \| all } [ vlan vlan-id ]	Available in user view
Clear the statistics information of all kinds of IGMP messages learned by IGMP Snooping	reset igmp-snooping statistics	Available in user view

& Note:

The reset igmp-snooping group command cannot clear IGMP Snooping multicast group information for static joins.

2.8 IGMP Snooping Configuration Examples

2.8.1 Configuring Simulated Joining

I. Network requirements

As shown in Figure 2-3, Router A connects to the multicast source through GigabitEthernet 1/0/2 and to Switch A through GigabitEthernet 1/0/1. Router A is the IGMP querier on the subnet.

Perform the following configuration so that multicast data can be forwarded through GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4 even if Host A and Host B temporarily stop receiving multicast data for some unexpected reasons.

II. Network diagram

Figure 2-3 Network diagram for simulated joining configuration

III. Configuration procedure

1) Configure the IP address of each interface

Configure an IP address and subnet mask for each interface as per Figure 2-3. The detailed configuration steps are omitted.

2) Configure Router A

# Enable IP multicast routing, enable PIM-DM on each interface, and enable IGMPv2 on GigabitEthernet 1/0/1.

<RouterA> system-view

[RouterA] multicast routing-enable

[RouterA] interface GigabitEthernet 1/0/1

[RouterA-GigabitEthernet1/0/1] igmp enable

[RouterA-GigabitEthernet1/0/1] pim dm

[RouterA-GigabitEthernet1/0/1] quit

[RouterA] interface GigabitEthernet 1/0/2

[RouterA-GigabitEthernet1/0/2] pim dm

[RouterA-GigabitEthernet1/0/2] quit

3) Configure Switch A

# Enable IGMP Snooping globally.

<SwitchA> system-view

[SwitchA] igmp-snooping

[SwitchA-igmp-snooping] quit

# Create VLAN 100, assign GigabitEthernet 1/0/1 through GigabitEthernet 1/0/4 to this VLAN, and enable IGMP Snooping in the VLAN.

[SwitchA] vlan 100

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

[SwitchA-vlan100] igmp-snooping enable

[SwitchA-vlan100] quit

# Enable simulated host joining on GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4 respectively.

[SwitchA] interface GigabitEthernet 1/0/3

[SwitchA-GigabitEthernet1/0/3] igmp-snooping host-join 224.1.1.1 vlan 100

[SwitchA-GigabitEthernet1/0/3] quit

[SwitchA] interface GigabitEthernet 1/0/4

[SwitchA-GigabitEthernet1/0/4] igmp-snooping host-join 224.1.1.1 vlan 100

[SwitchA-GigabitEthernet1/0/4] quit

4) Verify the configuration

# View the detailed information about IGMP Snooping multicast groups in VLAN 100 on Switch A.

[SwitchA] display igmp-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, A-Aggregation port, C-Copy 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.

GE1/0/1 (D) ( 00:01:30 )

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

IP group address:224.1.1.1

(0.0.0.0, 224.1.1.1):

Attribute: Host Port

Host port(s):total 2 port.

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

GE1/0/4 (D) ( 00:03:23 )

MAC group(s):

MAC group address:0100-5e01-0101

Host port(s):total 2 port.

GE1/0/3

GE1/0/4

As shown above, GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4 of Switch A have joined multicast group 224.1.1.1.

2.8.2 Static Router Port Configuration

I. Network requirements

l As shown in Figure 2-4, Router A connects to a multicast source (Source) through GigabitEthernet 1/0/2, and to Switch A through GigabitEthernet 1/0/1.

l IGMP is to run between Router A and Switch A, and IGMP Snooping is to run on Switch A, Switch B and Switch C, with Router A acting as the IGMP querier.

l Suppose STP runs on the network. To avoid data loops, the forwarding path from Switch A to Switch C is blocked under normal conditions, and multicast traffic flows to the receivers, Host A and Host C, attached to Switch C only along the path of Switch A—Switch B—Switch C.

l Now it is required to configure GigabitEthernet 1/0/3 that connects Switch A to Switch C as a static router port, so that multicast traffic can flows 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 IGMP query-response cycle must be completed before the multicast data can flow to the receivers along the new path of Switch A—Switch C, namely multicast delivery will be interrupted during this process.

II. Network diagram

Figure 2-4 Network diagram for static router port configuration

III. Configuration procedure

1) Configure the IP address of each interface

Configure an IP address and subnet mask for each interface as per Figure 2-4. The detailed configuration steps are omitted.

2) Configure Router A

# Enable IP multicast routing, enable PIM-DM on each interface, and enable IGMP on GigabitEthernet 1/0/1.

<RouterA> system-view

[RouterA] multicast routing-enable

[RouterA] interface GigabitEthernet 1/0/1

[RouterA-GigabitEthernet1/0/1] igmp enable

[RouterA-GigabitEthernet1/0/1] pim dm

[RouterA-GigabitEthernet1/0/1] quit

[RouterA] interface GigabitEthernet 1/0/2

[RouterA-GigabitEthernet1/0/2] pim dm

[RouterA-GigabitEthernet1/0/2] quit

3) Configure Switch A

# Enable IGMP Snooping globally.

<SwitchA> system-view

[SwitchA] igmp-snooping

[SwitchA-igmp-snooping] quit

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

[SwitchA] vlan 100

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

[SwitchA-vlan100] igmp-snooping enable

[SwitchA-vlan100] quit

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

[SwitchA] interface GigabitEthernet 1/0/3

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

[SwitchA-GigabitEthernet1/0/3] quit

4) Configure Switch B

# Enable IGMP Snooping globally.

<SwitchB> system-view

[SwitchB] igmp-snooping

[SwitchB-igmp-snooping] quit

# Create VLAN 100, assign GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 to this VLAN, and enable IGMP Snooping in the VLAN.

[SwitchB] vlan 100

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

[SwitchB-vlan100] igmp-snooping enable

[SwitchB-vlan100] quit

5) Configure Switch C

# Enable IGMP Snooping globally.

<SwitchC> system-view

[SwitchC] igmp-snooping

[SwitchC-igmp-snooping] quit

# Create VLAN 100, assign GigabitEthernet 1/0/1 through GigabitEthernet 1/0/5 to this VLAN, and enable IGMP Snooping in the VLAN.

[SwitchC] vlan 100

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

[SwitchC-vlan100] igmp-snooping enable

[SwitchC-vlan100] quit

6) Verify the configuration

# View the detailed information about IGMP Snooping multicast groups in VLAN 100 on Switch A.

[SwitchA] display igmp-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, A-Aggregation port, C-Copy 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.

GE1/0/1 (D) ( 00:01:30 )

GE1/0/3 (S)

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

IP group address:224.1.1.1

(0.0.0.0, 224.1.1.1):

Attribute: Host Port

Host port(s):total 1 port.

GE1/0/2 (D) ( 00:03:23 )

MAC group(s):

MAC group address:0100-5e01-0101

Host port(s):total 1 port.

GE1/0/2

As shown above, GigabitEthernet 1/0/3 of Switch A has become a static router port.

2.8.3 IGMP Snooping Querier Configuration

I. Network requirements

l As shown in Figure 2-5, in a Layer-2-only network environment, Switch C is connected to the multicast source (Source) through GigabitEthernet 1/0/3. At least one receiver is attached to Switch B and Switch C respectively.

l IGMPv2 is enabled on all the receivers. Switch A, Switch B, and Switch C run IGMP Snooping. Switch A acts as the IGMP-Snooping querier.

l Configure a non-all-zero IP address as the source IP address of IGMP queries to ensure normal creation of multicast forwarding entries.

II. Network diagram

Figure 2-5 Network diagram for IGMP Snooping querier configuration

III. Configuration procedure

1) Configure switch A

# Enable IGMP Snooping globally.

<SwitchA> system-view

[SwitchA] igmp-snooping

[SwitchA-igmp-snooping] quit

# Create VLAN 100 and add GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 to VLAN 100.

[SwitchA] vlan 100

[SwitchA-vlan100] port GigabitEthernet 1/0/1 GigabitEthernet 1/0/2

# Enable IGMP Snooping in VLAN 100 and configure the IGMP-Snooping querier feature.

[SwitchA-vlan100] igmp-snooping enable

[SwitchA-vlan100] igmp-snooping querier

# Set the source IP address of IGMP general queries and group-specific queries to 192.168.1.1.

[SwitchA-vlan100] igmp-snooping general-query source-ip 192.168.1.1

[SwitchA-vlan100] igmp-snooping special-query source-ip 192.168.1.1

2) Configure Switch B

# Enable IGMP Snooping globally.

<SwitchB> system-view

[SwitchB] igmp-snooping

[SwitchB-igmp-snooping] quit

# Create VLAN 100, add GigabitEthernet 1/0/1 through GigabitEthernet 1/0/3 to VLAN 100, and enable IGMP Snooping in this VLAN.

[SwitchB] vlan 100

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

[SwitchB-vlan100] igmp-snooping enable

3) Configuration on Switch C

# Enable IGMP Snooping globally.

<SwitchC> system-view

[SwitchC] igmp-snooping

[SwitchC-igmp-snooping] quit

# Create VLAN 100, add GigabitEthernet 1/0/1 through GigabitEthernet 1/0/3 to VLAN 100, and enable IGMP Snooping in this VLAN.

[SwitchC] vlan 100

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

[SwitchC-vlan100] igmp-snooping enable

4) Verify the configuration

# View the IGMP message statistics on Switch C.

[SwitchC-vlan100] display igmp-snooping statistics

Received IGMP general queries:3.

Received IGMPv1 reports:0.

Received IGMPv2 reports:4.

Received IGMP leaves:0.

Received IGMPv2 specific queries:0.

Sent IGMPv2 specific queries:0.

Received IGMPv3 reports:0.

Received IGMPv3 reports with right and wrong records:0.

Received IGMPv3 specific queries:0.

Received IGMPv3 specific sg queries:0.

Sent IGMPv3 specific queries:0.

Sent IGMPv3 specific sg queries:0.

Received error IGMP messages:0.

Switch C received IGMP general queries. This means that Switch A works as an IGMP-Snooping querier.

2.9 Troubleshooting IGMP Snooping Configuration

2.9.1 Switch Fails in Layer 2 Multicast Forwarding

I. Symptom

A switch fails to implement Layer 2 multicast forwarding.

II. Analysis

IGMP Snooping is not enabled.

III. Solution

1) Enter the display current-configuration command to view the running status of IGMP Snooping.

2) If IGMP Snooping is not enabled, use the igmp-snooping command to enable IGMP Snooping globally, and then use igmp-snooping enable command to enable IGMP Snooping in VLAN view.

3) If IGMP Snooping is disabled only for the corresponding VLAN, just use the igmp-snooping enable command in VLAN view to enable IGMP Snooping in the corresponding VLAN.

2.9.2 Configured Multicast Group Policy Fails to Take Effect

I. Symptom

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

II. Analysis

l The ACL rule is incorrectly configured.

l The multicast group policy is not correctly applied.

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

l Certain ports have been configured as static member ports of multicasts groups, and this configuration conflicts with the configured multicast group policy.

III. Solution

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

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

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

4) Use the display igmp-snooping group command to check whether any port has been configured as a static member port of any multicast group. If so, check whether this configuration conflicts with the configured multicast group policy. If any conflict exists, remove the port as a static member of the multicast group.

Chapter 3 MLD Snooping Configuration

When configuring MLD Snooping, go to these sections for information you are interested in:

l MLD Snooping Overview

l MLD Snooping Configuration Task List

l Displaying and Maintaining MLD Snooping

l MLD Snooping Configuration Examples

l Troubleshooting MLD Snooping

3.1 MLD Snooping Overview

Multicast Listener Discovery Snooping (MLD Snooping) is an IPv6 multicast constraining mechanism that runs on Layer 2 devices to manage and control IPv6 multicast groups.

3.1.1 Introduction to MLD Snooping

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 3-1, 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 3-1 Before and after MLD Snooping is enabled on the Layer 2 device

3.1.2 Basic Concepts in MLD Snooping

I. MLD Snooping related ports

As shown in Figure 2-2, 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 3-2 MLD Snooping related ports

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

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

l Member port: A member port (also known as IPv6 multicast group member port) is a port on the Ethernet switch that leads switch towards multicast group members. In the figure, Ethernet 1/0/2 and Ethernet 1/0/3 of Switch A and Ethernet 1/0/2 of Switch B are member ports. The switch registers all the member ports (including static and dynamic member ports) on the local device in its MLD Snooping forwarding table.

& Note:

l Whenever mentioned in this document, a router port is a router-connecting port on the switch, rather than a port on a router.

l 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 router ports.

II. Aging timers for dynamic ports in MLD Snooping

Table 3-1 Aging timers for dynamic ports in MLD Snooping and related messages and actions

Timer	Description	Message before expiry	Action after expiry
Router port aging timer	For each router port, the switch sets a timer initialized to the aging time of the route port.	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.
Member port aging timer	When a port joins an IPv6 multicast group, the switch sets a timer for the port, which is initialized to the member port aging time.	MLD report message.	The switch removes this port from the IPv6 multicast group forwarding table.

& Note:

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

3.1.3 How MLD Snooping Works

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

I. 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.

Upon receiving an MLD general query, the switch forwards it through all ports in the VLAN except the receiving port and performs the following to the receiving port:

l If the receiving port is a router port existing in its router port list, the switch resets the aging timer of this router port.

l If the receiving port is not a router port existing in its router port list, the switch adds it into its router port list and sets an aging timer for this router port.

II. Membership reports

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

l Upon receiving an MLD query, an IPv6 multicast group member host responds with an MLD report.

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

Upon 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:

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

l 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 member port to the outgoing port list, and starts a member port aging timer for that port.

l 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 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. The reason is as follows: Due to the MLD report suppression mechanism, 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 upon hearing this report, and this will prevent the switch from knowing whether any hosts attached to that port are still active members of the reported IPv6 multicast group.

III. 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 a group-specific MLD done message on a member port, it first checks whether a forwarding table entry for that IPv6 multicast group exists, and, if one exists, whether its outgoing port list contains that port.

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

l If the forwarding table entry exists and its outgoing port list contains the port, the switch forwards the done message to all router ports in the 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 removes the port from the outgoing port list of the forwarding table entry for that group; instead, it resets the member port aging timer for the port.

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

l If any MLD report in response to the MLD multicast-address-specific query is heard on a 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 of the member port.

l If no MLD report in response to the MLD multicast-address-specific query is heard on a member 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.

3.1.4 Protocols and Standards

MLD Snooping is documented in:

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

3.2 MLD Snooping Configuration Task List

Complete these tasks to configure MLD Snooping:

Task		Remarks
Configuring Basic Functions of MLD Snooping	Enabling MLD Snooping	Required
Configuring Basic Functions of MLD Snooping	Configuring the Version of MLD Snooping	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
Configuring MLD Snooping Querier	Enabling MLD Snooping Querier	Optional
	Configuring MLD Queries and Responses	Optional
	Configuring Source IPv6 Addresses of MLD Queries	Optional
Configuring an MLD Snooping Policy	Configuring an IPv6 Multicast Group Filter	Optional
	Configuring IPv6 Multicast Source Port Filtering	Optional
	Configuring Dropping Unknown IPv6 Multicast Data	Optional
	Configuring MLD Report Suppression	Optional
	Configuring Maximum Multicast Groups that that Can Be Joined on a Port	Optional
	Configuring IPv6 Multicast Group Replacement	Optional

& Note:

l Configurations made in MLD Snooping view are effective for all VLANs, while configurations made in VLAN view are effective only for ports belonging to the current VLAN. For a given VLAN, a configuration made in MLD Snooping view is effective only if the same configuration is not made in VLAN view.

l Configurations made in MLD Snooping view are effective for all ports; configurations made in Ethernet port view are effective only for the current port; configurations made in manual port group view are effective only for all the ports in the current port group; configurations made in aggregation group view are effective only for the master port. For a given port, a configuration made in MLD Snooping view is effective only if the same configuration is not made in Ethernet port view or port group view.

3.3 Configuring Basic Functions of MLD Snooping

3.3.1 Configuration Prerequisites

Before configuring the basic functions of MLD Snooping, complete the following tasks:

l Configure the corresponding VLANs

Before configuring the basic functions of MLD Snooping, prepare the following data:

l The version of MLD Snooping

3.3.2 Enabling MLD Snooping

Follow these steps to enable MLD Snooping:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enable MLD Snooping globally and enter MLD-Snooping view	mld-snooping	Required Disabled by default
Return to system view	quit	—
Enter VLAN view	vlan vlan-id	—
Enable MLD Snooping in the VLAN	mld-snooping enable	Required Disabled by default

& Note:

l MLD Snooping must be enabled globally before it can be enabled in a VLAN.

l After enabling MLD Snooping in a VLAN, you cannot enable MLD and/or IPv6 PIM on the corresponding VLAN interface, and vice versa.

l When you enable MLD Snooping in a specified VLAN, this function takes effect for Ethernet ports in this VLAN only.

3.3.3 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.

l MLD Snooping version 1 can process MLDv1 messages, but cannot analyze and process MLDv2 messages, which will be flooded in the VLAN.

l MLD Snooping version 2 can process MLDv1 and MLDv2 messages.

Follow these steps to configure the version of MLD Snooping:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Configure the version of MLD Snooping	mld-snooping version version-number	Optional Version 1 by default

Caution:

If you switch MLD Snooping from version 2 to version 1, the system will clear all MLD Snooping forwarding entries from dynamic joins, and will:

l Keep forwarding entries from version 2 static (*, G) joins;

l Clear forwarding entries from version 2 static (S, G) joins, which will be restored when MLD Snooping is switched back to version 2.

For details about static joins, Refer to Configuring Static Ports.

3.4 Configuring MLD Snooping Port Functions

3.4.1 Configuration Prerequisites

Before configuring MLD Snooping port functions, complete the following tasks:

l Enable MLD Snooping in the VLAN

l Configure the corresponding port groups

Before configuring MLD Snooping port functions, prepare the following data:

l Aging time of router ports

l Aging timer of member ports

l IPv6 multicast group and IPv6 multicast source addresses

3.4.2 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 aging timer of the port for that group expires.

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

I. Configuring aging timers for dynamic ports globally

Follow these steps to configure aging timers for dynamic ports globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter MLD Snooping view	mld-snooping	—
Configure router port aging time	router-aging-time interval	Optional 260 seconds by default
Configure member port aging time	host-aging-time interval	Optional 260 seconds by default

II. Configuring aging timers for dynamic ports in a VLAN

Follow these steps to configure aging timers for dynamic ports in a VLAN:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Configure router port aging time	mld-snooping router-aging-time interval	Optional 260 seconds by default
Configure member port aging time	mld-snooping host-aging-time interval	Optional 260 seconds by default

3.4.3 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 static router port, through which the switch can forward all IPv6 multicast data it received.

Follow these steps to configure static ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure the port(s) as static member port(s)		mld-snooping static-group ipv6-group-address [ source-ip ipv6-source-address ] vlan vlan-id	Required Disabled by default
Configure the port(s) as static router port(s)		mld-snooping static-router-port vlan vlan-id	Required Disabled by default

& Note:

l The IPv6 static (S, G) joining function is available only if a valid IPv6 multicast source address is specified and MLD Snooping version 2 is currently running on the switch.

l A static member port does not respond to queries from the MLD querier; when static (*, G) or (S, G) joining is enabled or disabled on a port, the port does not send an unsolicited MLD report or an MLD done message.

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

3.4.4 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 configure the port as a simulated member host for an IPv6 multicast group. When an MLD query is heard, simulated host gives a response. Thus, the switch can continue receiving IPv6 multicast data.

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

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

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

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

Follow these steps to configure simulated joining:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure simulated joining		mld-snooping host-join ipv6-group-address [ source-ip ipv6-source-address ] vlan vlan-id	Required Disabled by default

& Note:

l 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.

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

3.4.5 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.

I. Configuring fast leave processing globally

Follow these steps to configure fast leave processing globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter MLD Snooping view	mld-snooping	—
Enable fast leave processing	fast-leave [ vlan vlan-list ]	Required Disabled by default

II. Configuring fast leave processing on a port or a group of ports

Follow these steps to configure fast leave processing on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Enable fast leave processing		mld-snooping fast-leave [ vlan vlan-list ]	Required Disabled by default

Caution:

If fast leave processing is enabled on a port to which more than one host is connected, when one host leaves an IPv6 multicast group, the other hosts connected to port and interested in the same IPv6 multicast group will fail to receive IPv6 multicast data addressed to that group.

3.5 Configuring MLD Snooping Querier

3.5.1 Configuration Prerequisites

Before configuring MLD Snooping querier, complete the following task:

l Enable MLD Snooping in the VLAN.

Before configuring MLD Snooping querier, prepare the following data:

l MLD general query interval,

l MLD last-member query interval,

l Maximum response time for MLD general queries,

l Source IPv6 address of MLD general queries, and

l Source IPv6 address of MLD multicast-address-specific queries.

3.5.2 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.

Follow these steps to enable the MLD Snooping querier:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Enable the MLD Snooping querier	mld-snooping querier	Required 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 may affect MLD querier elections because it sends MLD general queries with a low source IPv6 address.

3.5.3 Configuring MLD Queries and Responses

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

Upon receiving an MLD query (general query or group-specific query), a host starts a timer for each IPv6 multicast group it has joined. This timer is initialized to a random value in the range of 0 to the maximum response time (the host obtains the value of the maximum response time from the Max Response Time field in the MLD query it received). When the timer value comes down to 0, the host sends an MLD report to the corresponding IPv6 multicast group.

An appropriate setting of the maximum response time for MLD queries allows hosts to respond to queries quickly and avoids burstiness of MLD traffic on the network caused by reports simultaneously sent by a large number of hosts when the corresponding timers expire simultaneously.

l For MLD general queries, you can configure the maximum response time to fill their Max Response time field.

l For MLD multicast-address-specific queries, you can configure the MLD last-member query interval to fill their Max Response time field. Namely, for MLD multicast-address-specific queries, the maximum response time equals to the MLD last-member query interval.

I. Configuring MLD queries and responses globally

Follow these steps to configure MLD queries and responses globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter MLD Snooping view	mld-snooping	—
Configure the maximum response time for MLD general queries	max-response-time interval	Optional 10 seconds by default
Configure the MLD last-member query interval	last-listener-query-interval interval	Optional 1 second by default

II. Configuring MLD queries and responses in a VLAN

Follow these steps to configure MLD queries and responses in a VLAN

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Configure MLD query interval	mld-snooping query-interval interval	Optional 125 seconds by default
Configure the maximum response time for MLD general queries	mld-snooping max-response-time interval	Optional 10 seconds by default
Configure the MLD last-member query interval	mld-snooping last-listener-query-interval interval	Optional 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 may occur.

3.5.4 Configuring Source IPv6 Addresses of MLD Queries

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

Follow these steps to configure source IPv6 addresses of MLD queries:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Configure the source IPv6 address of MLD general queries	mld-snooping general-query source-ip { current-interface \| ipv6-address }	Optional FE80::02FF:FFFF:FE00:0001 by default
Configure the source IPv6 address of MLD multicast-address-specific queries	mld-snooping special-query source-ip { current-interface \| ipv6-address }	Optional FE80::02FF:FFFF:FE00:0001 by default

Caution:

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

3.6 Configuring an MLD Snooping Policy

3.6.1 Configuration Prerequisites

Before configuring an MLD Snooping policy, complete the following tasks:

l Enable MLD Snooping in the VLAN

Before configuring an MLD Snooping policy, prepare the following data:

l IPv6 ACL rule for IPv6 multicast group filtering

l The maximum number of IPv6 multicast groups that can pass the ports

3.6.2 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. Upon receiving this report message, the switch checks the report against the configured ACL rule. If the port on which the report was heard 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.

I. Configuring an IPv6 multicast group filter globally

Follow these steps to configure an IPv6 multicast group globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter MLD Snooping view	mld-snooping	—
Configure an IPv6 multicast group filter	group-policy acl6-number [ vlan vlan-list ]	Required No IPv6 filter configured by default, namely hosts can join any IPv6 multicast group.

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

Follow these steps to configure an IPv6 multicast group filer on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure an IPv6 multicast group filter		mld-snooping group-policy acl6-number [ vlan vlan-list ]	Required No IPv6 filter configured by default, namely hosts can join any IPv6 multicast group.

3.6.3 Configuring IPv6 Multicast Source Port Filtering

With the IPv6 multicast source port filtering feature enabled on a port, the port can be connected with IPv6 multicast receivers only rather than with multicast sources, because the port will block all IPv6 multicast data packets while it permits multicast protocol packets to pass.

If this feature is disabled on a port, the port can be connected with both multicast sources and IPv6 multicast receivers.

I. Configuring IPv6 multicast source port filtering globally

Follow these steps to configure IPv6 multicast source port filtering:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter MLD Snooping view	mld-snooping	—
Enable IPv6 multicast source port filtering	source-deny port interface-list	Required Disabled by default

II. Configuring IPv6 multicast source port filtering on a port or a group of ports

Follow these steps to configure IPv6 multicast source port filtering on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Enable IPv6 multicast source port filtering		mld-snooping source-deny	Required Disabled by default

& Note:

When enabled to filter IPv6 multicast data based on the source ports, the device is automatically enabled to filter IPv4 multicast data based on the source ports.

3.6.4 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: When the switch receives such IPv6 multicast traffic:

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

l 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.

Follow these steps to enable dropping unknown IPv6 multicast data in a VLAN:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter VLAN view	vlan vlan-id	—
Enable dropping unknown IPv6 multicast data	mld-snooping drop-unknown	Required Disabled by default

& Note:

When enabled to drop unknown IPv6 multicast data, the device is automatically enabled to drop unknown IPv4 multicast data.

3.6.5 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.

Follow these steps to configure MLD report suppression:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter MLD Snooping view	mld-snooping	—
Enable MLD report suppression	report-aggregation	Optional Enabled by default

3.6.6 Configuring Maximum Multicast Groups that that Can Be Joined on a Port

By configuring the maximum number of IPv6 multicast groups that can be joined on a port or a group of ports, 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 can be joined on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure the maximum number of IPv6 multicast groups that can be joined on a port		mld-snooping group-limit limit [ vlan vlan-list ]	Optional The default is 128.

& Note:

l When the number of IPv6 multicast groups that can be joined on a port reaches the maximum number configured, the system deletes all the forwarding entries persistent to that port from the MLD Snooping forwarding table, and the hosts on this port need to join IPv6 multicast groups again.

l If you have configured static or simulated joins on a port, however, when the number of IPv6 multicast groups on the port exceeds the configured threshold, the system deletes all the forwarding entries persistent to that port from the MLD Snooping forwarding table and applies the static or simulated joins again, until the number of IPv6 multicast groups joined by the port comes back within the configured threshold.

3.6.7 Configuring IPv6 Multicast Group Replacement

For some special reasons, the number of IPv6 multicast groups passing through a switch or port may exceed the number configured for the switch or the port. In addition, in some specific applications, an IPv6 multicast group newly joined on the switch needs to replace an existing IPv6 multicast group automatically. A typical example is “channel switching”, namely, by joining the new multicast, a user automatically switches from the current IPv6 multicast group to the one.

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

l If the IPv6 multicast group replacement is enabled, the newly joined IPv6 multicast group automatically replaces an existing IPv6 multicast group with the lowest IPv6 address.

l If the IPv6 multicast group replacement is not enabled, new MLD reports will be automatically discarded.

I. Configuring IPv6 multicast group replacement globally

Follow these steps to configure IPv6 multicast group replacement globally:

To do...	Use the command...	Remarks
Enter system view	system-view	—
Enter MLD Snooping view	mld-snooping	—
Configure IPv6 multicast group replacement	overflow-replace [ vlan vlan-list ]	Required Disabled by default

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

Follow these steps to configure IPv6 multicast group replacement on a port or a group of ports:

To do...		Use the command...	Remarks
Enter system view		system-view	—
Enter the corresponding view	Enter Ethernet port view	interface interface-type interface-number	Use either command
Enter the corresponding view	Enter port group view	port-group { manual port-group-name \| aggregation agg-id }	Use either command
Configure IPv6 multicast group replacement		mld-snooping overflow-replace [ vlan vlan-list ]	Required Disabled by default

Caution:

Be sure to configure the maximum number of IPv6 multicast groups allowed on a port (refer to Configuring Maximum Multicast Groups that that Can Be Joined on a Port) before configuring IPv6 multicast group replacement. Otherwise, the IPv6 multicast group replacement functionality will not take effect.

3.7 Displaying and Maintaining MLD Snooping

To do…	Use the command...	Remarks
View the information about MLD Snooping multicast groups	display mld-snooping group [ vlan vlan-id ] [ verbose ]	Available in any view
View the statistics information of MLD messages learned by MLD Snooping	display mld-snooping statistics	Available in any view
Clear MLD Snooping multicast group information	reset mld-snooping group { ipv6-group-address \| all } [ vlan vlan-id ]	Available in user view
Clear the statistics information of all kinds of MLD messages learned by MLD Snooping	reset mld-snooping statistics	Available in user view

& Note:

The reset mld-snooping group command cannot clear MLD Snooping multicast group information for static joins.

3.8 MLD Snooping Configuration Examples

3.8.1 Simulated Joining

I. Network requirements

As shown in Figure 3-3, Router A connects to the IPv6 multicast source through GigabitEthernet 1/0/2 and to Switch A through GigabitEthernet 1/0/1. Router A is the MLD querier on the subnet.

II. Network diagram

Figure 3-3 Network diagram for simulated joining configuration

III. Configuration procedure

1) Enable IPv6 forwarding and configure the IPv6 address of each interface

Enable IPv6 forwarding and configure an IPv6 address and prefix length for each interface as per Figure 3-3. The detailed configuration steps are omitted.

2) Configure Router A

# Enable IPv6 multicast routing, enable IPv6 PIM-DM on each interface, and enable MLDv1 on GigabitEthernet 1/0/1.

<RouterA> system-view

[RouterA] multicast ipv6 routing-enable

[RouterA] interface GigabitEthernet 1/0/1

[RouterA-GigabitEthernet1/0/1] mld enable

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

[RouterA-GigabitEthernet1/0/1] quit

[RouterA] interface GigabitEthernet 1/0/2

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

[RouterA-GigabitEthernet1/0/2] quit

3) Configure Switch A

# Enable MLD Snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

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

[SwitchA] vlan 100

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

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] quit

# Enable simulated host joining on GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4.

[SwitchA] interface GigabitEthernet 1/0/3

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

[SwitchA-GigabitEthernet1/0/3] quit

[SwitchA] interface GigabitEthernet 1/0/4

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

[SwitchA-GigabitEthernet1/0/4] quit

4) Verify the configuration

# View the detailed information about MLD Snooping multicast groups 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, A-Aggregation port, C-Copy 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.

GE1/0/1 (D) ( 00:01:30 )

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.

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

GE1/0/4 (D) ( 00:03:23 )

MAC group(s):

MAC group address:3333-0000-1001

Host port(s):total 2 port.

GE1/0/3

GE1/0/4

As shown above, GigabitEthernet 1/0/3 and GigabitEthernet 1/0/4 of Switch A have joined IPv6 multicast group FF1E::101.

3.8.2 Static Router Port Configuration

I. Network requirements

l As shown in Figure 3-4, Router A connects to an IPv6 multicast source (Source) through GigabitEthernet 1/0/2, and to Switch A through GigabitEthernet 1/0/1.

l MLD is to run between Router A and Switch A, and MLD Snooping is to run on Switch A, Switch B and Switch C, with Router A acting as the MLD querier.

l Suppose 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, Host A and Host C, attached to Switch C only along the path of Switch A—Switch B—Switch C.

l Now it is required to configure GigabitEthernet 1/0/3 that connects Switch A to Switch C as a static router port, so that IPv6 multicast traffic can flows 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.

II. Network diagram

Figure 3-4 Network diagram for static router port configuration

III. Configuration procedure

1) Enable IPv6 forwarding and configure the IPv6 address of each interface

Enable IPv6 forwarding and configure an IP address and prefix length for each interface as per Figure 3-4.

2) Configure Router A

# Enable IPv6 multicast routing, enable IPv6 PIM-DM on each interface, and enable MLD on GigabitEthernet 1/0/1.

<RouterA> system-view

[RouterA] multicast ipv6 routing-enable

[RouterA] interface GigabitEthernet 1/0/1

[RouterA-GigabitEthernet 1/0/1] mld enable

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

[RouterA-GigabitEthernet 1/0/1] quit

[RouterA] interface GigabitEthernet 1/0/2

[RouterA-GigabitEthernet 1/0/2] pim ipv6 dm

[RouterA-GigabitEthernet 1/0/2] quit

3) Configure Switch A

# Enable MLD Snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

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

[SwitchA] vlan 100

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

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] quit

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

[SwitchA] interface GigabitEthernet 1/0/3

[SwitchA-GigabitEthernet 1/0/3] mld-snooping static-router-port vlan 100

[SwitchA-GigabitEthernet 1/0/3] quit

4) Configure Switch B

# Enable MLD Snooping globally.

<SwitchB> system-view

[SwitchB] mld-snooping

[SwitchB-mld-snooping] quit

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

[SwitchB] vlan 100

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

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

[SwitchC] vlan 100

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

[SwitchC-vlan100] mld-snooping enable

[SwitchC-vlan100] quit

6) Verify the configuration

# View the detailed information about MLD Snooping multicast groups 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, A-Aggregation port, C-Copy 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.

GE1/0/1 (D) ( 00:01:30 )

GE1/0/3 (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.

GE1/0/2 (D) ( 00:03:23 )

MAC group(s):

MAC group address:3333-0000-0101

Host port(s):total 1 port.

GE1/0/2

As shown above, GigabitEthernet 1/0/3 of Switch A has become a static router port.

3.8.3 MLD Snooping Querier Configuration

I. Network requirements

l As shown in Figure 2-5, in a Layer-2-only network environment, Switch C is attached to the multicast source (Source) through GigabitEthernet 1/0/3. At least one receiver is connected to Switch B and Switch C respectively.

l MLDv1 is enabled on all the receivers. Switch A, Switch B, and Switch C run MLD Snooping. Switch A acts as the MLD Snooping querier.

II. Network diagram

Figure 3-5 Network diagram for MLD Snooping querier configuration

III. 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 add GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 to VLAN 100.

[SwitchA] vlan 100

[SwitchA-vlan100] port GigabitEthernet 1/0/1 GigabitEthernet 1/0/2

# Enable MLD Snooping in VLAN 100 and configure the MLD-Snooping querier feature.

[SwitchA-vlan100] mld-snooping enable

[SwitchA-vlan100] mld-snooping querier

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 1/0/1 through GigabitEthernet 1/0/3 into VLAN 100, and enable MLD Snooping in this VLAN.

[SwitchB] vlan 100

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

[SwitchB-vlan100] mld-snooping enable

3) Configuration on Switch C

# Enable IPv6 forwarding and enable MLD Snooping globally.

<SwitchC> system-view

[SwitchC] ipv6

[SwitchC] mld-snooping

[SwitchC-mld-snooping] quit

# Create VLAN 100, add GigabitEthernet 1/0/1 through GigabitEthernet 1/0/3 to VLAN 100, and enable MLD Snooping in this VLAN.

[SwitchC] vlan 100

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

[SwitchC-vlan100] mld-snooping enable

4) Verify the configuration

# View the MLD message statistics on Switch C.

[SwitchC-vlan100] display mld-snooping statistics

Received MLD general queries:3.

Received MLDv1 specific queries:0.

Received MLDv1 reports:4.

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.

Switch C received MLD general queries. This means that Switch A works as an MLD-Snooping querier.

3.9 Troubleshooting MLD Snooping

3.9.1 Switch Fails in Layer 2 Multicast Forwarding

I. Symptom

A switch fails to implement Layer 2 multicast forwarding.

II. Analysis

MLD Snooping is not enabled.

III. Solution

1) Enter the 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 mld-snooping enable command to enable MLD Snooping in VLAN view.

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

3.9.2 Configured IPv6 Multicast Group Policy Fails to Take Effect

I. 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.

II. Analysis

l The IPv6 ACL rule is incorrectly configured.

l The IPv6 multicast group policy is not correctly applied.

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

l Certain ports have been configured as static member ports of IPv6 multicasts groups, and this configuration conflicts with the configured IPv6 multicast group policy.

III. 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 whether the function of dropping unknown IPv6 multicast data is enabled. If not, use the mld-snooping drop-unknown command to enable the function of dropping unknown IPv6 multicast data.

4) Use the display mld-snooping group command to check whether any port has been configured as a static member port of any IPv6 multicast group. If so, check whether this configuration conflicts with the configured IPv6 multicast group policy. If any conflict exists, remove the port as a static member of the IPv6 multicast group.

Chapter 4 Multicast VLAN Configuration

4.1 Introduction to Multicast VLAN

As shown in Figure 4-1, in the traditional multicast programs-on-demand mode, when hosts that belong to different VLANs, Host A, Host B and Host C require multicast programs on demand service, Router A needs to forward a separate copy of the multicast data in each VLAN. This results in not only waste of network bandwidth but also extra burden on the Layer 3 device.

Figure 4-1 Before and after multicast VLAN is enabled on the Layer 2 device

To solve this problem, you can enable the multicast VLAN feature on Switch A, namely configure the VLANs to which these hosts belong as sub-VLANs of a multicast VLAN on the Layer 2 device and enable Layer 2 multicast in the multicast VLAN. After this configuration, Router A replicates the multicast data only within the multicast VLAN instead of forwarding a separate copy of the multicast data to each VLAN. This saves the network bandwidth and lessens the burden of the Layer 3 device.

4.2 Configuring Multicast VLAN

Follow these steps to configure a multicast VLAN:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Configure a specific VLAN as a multicast VLAN	multicast-vlan vlan-id enable	Required Disabled by default
Configure sub-VLANs for a specific multicast VLAN	multicast-vlan vlan-id subvlan vlan-list	Required No sub-VLAN by default.

& Note:

l The VLAN to be configured as the multicast VLAN and the VLANs to be configured as sub-VLANs of the multicast VLAN must exist.

l The number of sub-VLANs of the multicast VLAN must not exceed the system-defined limit (an S5500-SI series Ethernet switch supports a maximum of one multicast VLAN and 63 sub-VLANs).

Caution:

After a VLAN is configured into a multicast VLAN, IGMP Snooping must be enabled in the VLAN before the multicast VLAN feature can be implemented, while it is not necessary to enable IGMP Snooping in the sub-VLANs of the multicast VLAN.

4.3 Displaying and Maintaining Multicast VLAN

To do…	Use the command…	Remarks
Display information about a multicast VLAN and its sub-VLANs	display multicast-vlan [ vlan-id ]	Available in any view

4.4 Multicast VLAN Configuration Example

I. Network requirements

l Router A connects to a multicast source through GigabitEthernet 1/0/2 and to Switch A, through GigabitEthernet 1/0/1.

l IGMP is required on Router A and Switch A, and IGMP Snooping is required on Switch A. Router A is the IGMP querier.

l Switch A’s GigabitEthernet 1/0/1 belongs to VLAN 1024, GigabitEthernet 1/0/2 through GigabitEthernet 1/0/4 belong to VLAN 11 through VLAN 13 respectively, and Host A through Host C are attached to GigabitEthernet 1/0/2 through GigabitEthernet 1/0/4 of Switch A.

l Configure the multicast VLAN feature so that Router A just sends multicast data to VLAN 1024 rather than to each VLAN when the three hosts attached to Switch A need the multicast data.

II. Network diagram

Figure 4-2 Network diagram for multicast VLAN configuration

III. Configuration procedure

1) Configure an IP address for each interconnecting interface

Configure an IP address and subnet mask for each interface as per Figure 4-2. The detailed configuration steps are omitted here.

2) Configure Router A

# Enable IP multicast routing, enable PIM-DM on each interface and enable IGMP on GigabitEthernet 1/0/1.

<RouterA> system-view

[RouterA] multicast routing-enable

[RouterA] interface GigabitEthernet 1/0/1

[RouterA-GigabitEthernet 1/0/1] pim dm

[RouterA-GigabitEthernet 1/0/1] igmp enable

[RouterA-GigabitEthernet 1/0/1] quit

[RouterA] interface GigabitEthernet 1/0/2

[RouterA-GigabitEthernet 1/0/2] pim dm

[RouterA-GigabitEthernet 1/0/2] quit

3) Configure Switch A

# Enable IGMP Snooping globally.

<SwitchA> system-view

[SwitchA] igmp-snooping

[SwitchA-igmp-snooping] quit

# Create VLAN 11 and assign GigabitEthernet 1/0/2 to this VLAN.

[SwitchA] vlan 11

[SwitchA-vlan11] port GigabitEthernet 1/0/2

[SwitchA-vlan11] quit

The configuration for VLAN 12 and VLAN 13 is similar to the configuration for VLAN 11.

# Create VLAN 1024, assign GigabitEthernet 1/0/1 to this VLAN and enable IGMP Snooping in the VLAN.

[SwitchA] vlan 1024

[SwitchA-vlan1024] port GigabitEthernet 1/0/1

[SwitchA-vlan1024] igmp-snooping enable

[SwitchA-vlan1024] quit

# Configure VLAN 1024 as multicast VLAN and configure VLAN 11 through VLAN 13 as its sub-VLANs.

[SwitchA] multicast-vlan 1024 enable

[SwitchA] multicast-vlan 1024 subvlan 11 to 13

4) Verify the configuration

# Display information about the multicast VLAN and its sub-VLANs.

[SwitchA] display multicast-vlan

multicast vlan 1024's subvlan list:

Vlan 11-13

Chapter 5 IPv6 Multicast VLAN Configuration

5.1 Introduction to IPv6 Multicast VLAN

As shown in Figure 5-1, in the traditional IPv6 multicast programs-on-demand mode, when hosts that belong to different VLANs, Host A, Host B and Host C require IPv6 multicast programs on demand service, Router A needs to forward a separate copy of the IPv6 multicast data in each VLAN. This results in not only waste of network bandwidth but also extra burden on the Layer 3 device.

Figure 5-1 Before and after IPv6 multicast VLAN is enabled on the Layer 2 device

To solve this problem, you can enable the IPv6 multicast VLAN feature on Switch A, namely configure the VLANs to which these hosts belong as sub-VLANs of an IPv6 multicast VLAN on the Layer 2 device and enable IPv6 Layer 2 multicast in the IPv6 multicast VLAN. After this configuration, Router A replicates the IPv6 multicast data only within the IPv6 multicast VLAN instead of forwarding a separate copy of the IPv6 multicast data to each VLAN. This saves the network bandwidth and lessens the burden of the Layer 3 device.

5.2 Configuring IPv6 Multicast VLAN

Follow these steps to configure IPv6 VLAN

To do…	Use the command…	Remarks
Enter system view	system-view	—
Configure a specific VLAN as an IPv6 multicast VLAN	multicast-vlan ipv6 vlan-id enable	Required By default, no VLAN is an IPv6 multicast VLAN.
Configure sub-VLANs for a multicast VLAN	multicast-vlan ipv6 vlan-id subvlan vlan-list	Required By default, no sub-VLANs exist.

& Note:

l The VLAN to be configured as an IPv6 multicast VLAN and the VLANs to be configured as sub-VLANs of the IPv6 multicast VLAN must exist.

l The total number of sub-VLANs of an IPv6 multicast VLAN must not exceed the system-defined limit (an S5500-SI series Ethernet switch supports a maximum of one IPv6 multicast VLAN and 63 sub-VLANs).

Caution:

l You cannot enable IPv6 multicast VLAN on a device with IPv6 multicast routing enabled.

l After a VLAN is configured into an IPv6 multicast VLAN, MLD Snooping must be enabled in the VLAN before the IPv6 multicast VLAN feature can be implemented, while it is not necessary to enable MLD Snooping in the sub-VLANs of the IPv6 multicast VLAN.

5.3 Displaying and Maintaining IPv6 Multicast VLAN

To do…	Use the command…	Remarks
Display information about an IPv6 multicast VLAN and its sub-VLANs	display multicast-vlan ipv6 [ vlan-id ]	Available in any view

5.4 IPv6 Multicast VLAN Configuration Examples

I. Network requirements

l As shown in Figure 5-2, Router A connects to an IPv6 multicast source (Source) through GigabitEthernet 1/0/2, and to Switch A through GigabitEthernet 1/0/1.

l Router A is an IPv6 multicast router while Switch A is a Layer 2 switch. Router A acts as the MLD querier on the subnet.

l Configure the IPv6 multicast VLAN feature so that Router A just sends IPv6 multicast data to VLAN 1024 rather than to each VLAN when the three hosts attached to Switch A need the IPv6 multicast data.

II. Network diagram

Figure 5-2 Network diagram for IPv6 multicast VLAN configuration

III. Configuration procedure

1) Enable IPv6 forwarding and configure IPv6 addresses of the interfaces of each device.

Enable IPv6 forwarding and configure the IPv6 address and address prefix for each interface as per Figure 5-2. The detailed configuration steps are omitted here.

2) Configure Router A

# Enable IPv6 multicast routing, enable IPv6 PIM-DM on each interface, and enable MLD on GigabitEthernet 1/0/1.

<RouterA> system-view

[RouterA] multicast ipv6 routing-enable

[RouterA] interface GigabitEthernet 1/0/1

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

[RouterA-GigabitEthernet1/0/1] mld enable

[RouterA-GigabitEthernet1/0/1] quit

[RouterA] interface GigabitEthernet1/0/2

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

[RouterA-GigabitEthernet1/0/2] quit

3) Configure Switch A

# Enable MLD Snooping globally.

<SwitchA> system-view

[SwitchA] mld-snooping

[SwitchA-mld-snooping] quit

# Create VLAN 11 and add GigabitEthernet 1/0/2 into VLAN 11.

[SwitchA] vlan 11

[SwitchA-vlan11] port GigabitEthernet 1/0/2

[SwitchA-vlan11] quit

The configuration for VLAN 12 and VLAN 13 is similar. The detailed configuration steps are omitted.

# Create VLAN 1024, add GigabitEthernet 1/0/1 to VLAN 1024, and enable MLD Snooping in this VLAN.

[SwitchA] vlan 1024

[SwitchA-vlan1024] port GigabitEthernet 1/0/1

[SwitchA-vlan1024] mld-snooping enable

[SwitchA-vlan1024] quit

# Configure VLAN 1024 as an IPv6 multicast VLAN, and configure VLAN 11 through VLAN 13 as its sub-VLANs.

[SwitchA] multicast-vlan ipv6 1024 enable

[SwitchA] multicast-vlan ipv6 1024 subvlan 11 to 13

4) Verify the configuration

# Display IPv6 multicast VLAN and sub-VLAN information on Switch A.

[SwitchA] display multicast-vlan ipv6

IPv6 multicast vlan 1024's subvlan list:

vlan 11-13

H3C S5500-SI Series Ethernet Switches Operation Manual(V1.01)

I. Unicast

III. Multicast

I. Advantages of multicast

II. Applications of multicast

I. ASM model

II. SSM model

III. Ethernet multicast MAC addresses

1.3.2 Multicast Protocols

I. Layer 3 multicast protocols

II. Layer 2 multicast protocols

1.4 Multicast Packet Forwarding Mechanism

2.1 IGMP Snooping Overview

I. IGMP Snooping related ports

II. Aging timers for dynamic ports in IGMP Snooping and related messages and actions

I. When receiving a general query

II. When receiving a membership report

III. When receiving a leave group message

2.3 Configuring Basic Functions of IGMP Snooping

2.3.2 Enabling IGMP Snooping

2.3.3 Configuring the Version of IGMP Snooping

2.4 Configuring IGMP Snooping Port Functions

2.4.2 Configuring Aging Timers for Dynamic Ports

I. Configuring aging timers for dynamic ports globally

II. Configuring aging timers for dynamic ports in a VLAN

2.4.4 Configuring Simulated Joining

2.4.5 Configuring Fast Leave Processing

I. Configuring fast leave processing globally

II. Configuring fast leave processing on a port or a group of ports

2.5 Configuring IGMP Snooping Querier

2.5.2 Enabling IGMP Snooping Querier

2.5.3 Configuring IGMP Queries and Responses

I. Configuring IGMP queries and responses globally

II. Configuring IGMP queries and responses in a VLAN

2.5.4 Configuring Source IP Address of IGMP Queries

2.6 Configuring an IGMP Snooping Policy

2.6.2 Configuring a Multicast Group Filter

I. Configuring a multicast group filter globally

II. Configuring a multicast group filter on a port or a group of ports

2.6.3 Configuring Multicast Source Port Filtering

I. Configuring multicast source port filtering globally

II. Configuring multicast source port filtering on a port or a group of ports

2.6.4 Configuring the Function of Dropping Unknown Multicast Data

2.6.7 Configuring Multicast Group Replacement

I. Configuring multicast group replacement globally

II. Configuring multicast group replacement on a port or a group of ports

2.7 Displaying and Maintaining IGMP Snooping

I. Network requirements

II. Network diagram

III. Configuration procedure

I. Network requirements

II. Network diagram

III. Configuration procedure

I. Network requirements

II. Network diagram

III. Configuration procedure

I. Symptom

II. Analysis

III. Solution

I. Symptom

II. Analysis

III. Solution

3.1 MLD Snooping Overview

I. MLD Snooping related ports

II. Aging timers for dynamic ports in MLD Snooping

I. General queries

II. Membership reports

III. Done messages

3.3 Configuring Basic Functions of MLD Snooping

3.3.2 Enabling MLD Snooping

3.4 Configuring MLD Snooping Port Functions

3.4.2 Configuring Aging Timers for Dynamic Ports

I. Configuring aging timers for dynamic ports globally

II. Configuring aging timers for dynamic ports in a VLAN

3.4.5 Configuring Fast Leave Processing

I. Configuring fast leave processing globally

II. Configuring fast leave processing on a port or a group of ports

3.5 Configuring MLD Snooping Querier

3.5.2 Enabling MLD Snooping Querier

3.5.3 Configuring MLD Queries and Responses