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

IGMP snooping principle

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

As shown in Figure 1, when IGMP snooping is not running on the switch, multicast packets are flooded 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 1 Before and after IGMP snooping is enabled on the Layer 2 device

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

· Reducing Layer 2 broadcast packets, thus saving network bandwidth.

· Enhancing the security of multicast traffic.

· Facilitating the implementation of per-host accounting.

Basic concepts in IGMP snooping

IGMP snooping related ports

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

Figure 2 IGMP snooping related ports

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

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

· Member port—A member port is a port on an Ethernet switch that leads the switch toward multicast group members. In the figure, GigabitEthernet 3/0/2 and GigabitEthernet 3/0/3 of Device A and GigabitEthernet 3/0/2 of Device B are member ports. The switch registers all the member ports on the local device in its IGMP snooping forwarding table.

NOTE:

· 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.

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

· An IGMP-snooping-enabled switch deems that all its ports on which IGMP general queries with the source IP address other than 0.0.0.0 or PIM hello messages are received are dynamic router ports. For more information about PIM hello messages, see the chapter “Configuring PIM.”

Aging timers for dynamic ports in IGMP snooping and related messages and actions

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

Timer	Description	Message before expiry	Action after expiry
Dynamic router port aging timer	For each dynamic router port, the switch sets a timer initialized to the dynamic router port aging time.	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.
Dynamic member port aging timer	When a port dynamically joins a multicast group, the switch sets a timer for the port, which is initialized to the dynamic member port aging time.	IGMP membership report	The switch removes this port from the IGMP snooping forwarding table.

NOTE:

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

How IGMP snooping works

A switch that is running IGMP snooping performs different actions when it receives different IGMP messages.

CAUTION:

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

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 determine whether active multicast group members exist on the subnet.

After 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:

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

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

When receiving a membership report

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

· After receiving an IGMP query, a multicast group member host responds with an IGMP report.

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

After 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 operation:

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

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

· 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 dynamic member port, the switch resets the aging timer for that port.

NOTE:

A switch does not forward an IGMP report through a non-router port. This is because if the switch forwards a report message through a member port, all the attached hosts listening to the reported multicast address will suppress their own reports after receiving this report according to the IGMP report suppression mechanism on them, and this will prevent the switch from knowing whether the reported multicast group still has active members attached to that port. For more information about the IGMP report suppression mechanism on hosts, see the chapter “Configuring IGMP.”

When receiving a leave message

When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave 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 dynamic 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 message to the multicast router. When the switch receives an IGMP leave message on a dynamic member port, the switch first checks whether a forwarding table entry for the group address in the message exists, and, if one exists, whether the outgoing port list contains the port.

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

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

After receiving the IGMP leave message from a host, the IGMP querier resolves the multicast group address in the message and sends an IGMP group-specific query to that multicast group through the port that received the leave message. After receiving 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 operation to the port that received the IGMP leave message:

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

· If no IGMP report in response to the group-specific query is received on the port before its aging timer expires, this means that no hosts attached to the port are still listening to that 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.

IGMP snooping proxying

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

NOTE:

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

Figure 3 Network diagram

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

Table 2 IGMP message processing on an IGMP snooping proxy

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

Protocols and standards

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

IGMP snooping configuration task list

Complete these tasks to configure IGMP snooping:

Task		Remarks
Configuring basic IGMP snooping functions	Enabling IGMP snooping	Required
	Configuring the version of IGMP snooping	Optional
	Configuring the maximum number of global IGMP forwarding entries	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
	Disabling a port from becoming a dynamic router port	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 IGMP snooping proxying	Enabling IGMP snooping proxying	Optional
Configuring IGMP snooping proxying	Configuring a source IP address for the IGMP messages sent by the proxy	Optional
Configuring an IGMP snooping policy	Configuring a multicast group filter	Optional
	Enabling dropping unknown multicast data	Optional
	Configuring IGMP report suppression	Optional
	Configuring multicast group replacement	Optional
	Enabling the IGMP snooping host tracking function	Optional

NOTE:

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

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

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

Configuring basic IGMP snooping functions

Configuration prerequisites

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

· Configure the corresponding VLANs

· Determine the version of IGMP snooping

Enabling IGMP snooping

To enable IGMP snooping:

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

NOTE:

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

· After you enable IGMP snooping in a VLAN, do not enable IGMP or PIM on the corresponding VLAN interface.

· When you enable IGMP snooping in a specified VLAN, IGMP snooping works only on the ports in this VLAN.

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.

· IGMPv2 snooping can process IGMPv1 and IGMPv2 messages, but cannot process IGMPv3 messages, which will be flooded in the VLAN.

· IGMPv3 snooping can process IGMPv1, IGMPv2 and IGMPv3 messages.

To configure the version of IGMP snooping:

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

CAUTION:

If you change IGMPv3 snooping to IGMPv2 snooping, the system clears all IGMP snooping forwarding entries that are dynamically added, and also does the following:

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

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

For more information about static joins, see “Configuring static ports.”

Configuring the maximum number of global IGMP forwarding entries

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

To configure the maximum number of entries in the forwarding table

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

NOTE:

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

Configuring IGMP snooping port functions

Configuration prerequisites

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

· Enable IGMP snooping in the VLAN

· Configure the corresponding port groups

· Determine the aging time of dynamic router ports

· Determine the aging time of dynamic member ports

· Determine the multicast group and multicast source addresses

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 dynamic member port aging timer, and vice versa.

Configuring aging timers for dynamic ports globally

To configure aging timers for dynamic ports globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Configure dynamic router port aging time.	router-aging-time interval	105 seconds by default
4. Configure dynamic member port aging time.	host-aging-time interval	260 seconds by default

Configuring aging timers for dynamic ports in a VLAN

To configure aging timers for dynamic ports in a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Configure dynamic router port aging time.	igmp-snooping router-aging-time interval	105 seconds by default
4. Configure dynamic member port aging time.	igmp-snooping host-aging-time interval	260 seconds by default

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, you can 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.

To configure static ports:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Configure the port or ports as static member port or ports.	igmp-snooping static-group group-address [ source-ip source-address ] vlan vlan-id	No static member ports by default.
4. Configure the port or ports as static router port or ports.	igmp-snooping static-router-port vlan vlan-id	No static router ports by default.

NOTE:

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

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

Configuring simulated joining

Generally, a host running IGMP responds to IGMP queries from the IGMP querier. If a host fails to respond due to some reasons, the multicast router might 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, you can enable simulated joining on a port of the switch. Namely, you can configure the port as a simulated member host for a multicast group. When receiving an IGMP query, the simulated host gives a response. Thus, the switch can continue receiving multicast data.

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

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

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

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

To configure simulated joining:

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

NOTE:

· 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.

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

Configuring fast-leave processing

The fast-leave processing feature allows the switch to process IGMP leave messages in a fast way. With the fast-leave processing feature enabled, when receiving an IGMP leave 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. However, if fast-leave processing is enabled on a port to which more than one host is attached, when one host leaves a multicast group, the other hosts attached to the port and interested in the same multicast group will fail to receive multicast data for that group. Therefore, if the function of dropping unknown multicast traffic is already enabled on the switch or in the VLANs, the fast-leave processing function should not be enabled.

Configuring fast-leave processing globally

To configure fast-leave processing globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Enable fast-leave processing.	fast-leave [ vlan vlan-list ]	Disabled by default

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

To configure fast-leave processing on a port or a group of ports:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Enable fast-leave processing.	igmp-snooping fast-leave [ vlan vlan-list ]	Disabled by default.

Disabling a port from becoming a dynamic router port

The following problems exist in a multicast access network:

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

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

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

To disable a port from becoming a dynamic router port:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Disable the port from becoming a dynamic router port.	igmp-snooping router-port-deny [ vlan vlan-list ]	By default, a port can become a dynamic router port.

NOTE:

This configuration does not affect the static router port configuration.

Configuring IGMP snooping querier

Configuration prerequisites

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

· Enable IGMP snooping in the VLAN

· Determine the IGMP general query interval

· Determine the IGMP last-member query interval

· Determine the maximum response time to IGMP general queries

· Determine the source address of IGMP general queries

· Determine the source address of IGMP group-specific queries

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 the “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.

To enable IGMP snooping querier:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Enable IGMP snooping querier.	igmp-snooping querier	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 might affect IGMP querier elections because it sends IGMP general queries with a low source IP address. For more information about IGMP querier, see the chapter “Configuring IGMP.”

Configuring IGMP queries and responses

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

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

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

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

· For IGMP group-specific queries, the maximum response time equals to the IGMP last-member query interval.

Configuring IGMP queries and responses globally

To configure IGMP queries and responses globally:

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

Configuring IGMP queries and responses in a VLAN

To configure IGMP queries and responses in a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Configure IGMP general query interval.	igmp-snooping query-interval interval	60 seconds by default
4. Configure the maximum response time for IGMP general queries.	igmp-snooping max-response-time interval	10 seconds by default
5. Configure the IGMP last-member query interval.	igmp-snooping last-member-query-interval interval	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 might be deleted by mistake.

Configuring source IP address of IGMP queries

After receiving an IGMP query whose source IP address is 0.0.0.0 on a port, the switch does not enlist that port as a dynamic router port. This might 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.

To configure source IP address of IGMP queries:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Configure the source address of IGMP general queries.	igmp-snooping general-query source-ip { ip-address \| current-interface }	0.0.0.0 by default
4. Configure the source IP address of IGMP group-specific queries.	igmp-snooping special-query source-ip { ip-address \| current-interface }	0.0.0.0 by default

CAUTION:

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

Configuring IGMP snooping proxying

Configuration prerequisites

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

· Enable IGMP snooping in the VLAN

· Determine the source IP address for the IGMP reports sent by the proxy

· Determine the source IP address for the IGMP leave messages sent by the proxy

Enabling IGMP snooping proxying

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

To enable IGMP snooping proxying in a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Enable IGMP snooping proxying in the VLAN.	igmp-snooping proxying enable	Disabled by default.

Configuring a source IP address for the IGMP messages sent by the proxy

You can set the source IP addresses in the IGMP reports and leave messages sent by the IGMP snooping proxy on behalf of its attached hosts.

To configure the source IP addresses for the IGMP messages sent by the IGMP snooping proxy on behalf of its attached hosts in a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Configure a source IP address for the IGMP reports sent by the proxy.	igmp-snooping report source-ip { ip-address \| current-interface }	The default is 0.0.0.0.
4. Configure a source IP address for the IGMP leave messages sent by the proxy.	igmp-snooping leave source-ip { ip-address \| current-interface }	The default is 0.0.0.0.

Configuring an IGMP snooping policy

Configuration prerequisites

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

· Enable IGMP snooping in the VLAN

· Determine the ACL rule for multicast group filtering

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

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. After receiving this report message, the switch checks the report against the configured ACL rule. If the port on which the report was received can join this 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 multicast programs provided for multicast users.

Configuring a multicast group filter globally

To configure a multicast group filter globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Configure a multicast group filter.	group-policy acl-number [ vlan vlan-list ]	By default, no group filter is globally configured. That is, hosts in VLANs can join any valid multicast group.

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

To configure a multicast group filter on a port or a group of ports:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Configure a multicast group filter.	igmp-snooping group-policy acl-number [ vlan vlan-list ]	By default, no group filter is configured on the current port. That is, hosts on this port can join any valid multicast group.

Enabling dropping unknown multicast data

Unknown multicast data refers to multicast data for which no forwarding entries exist in the IGMP snooping forwarding table. After the switch receives such multicast traffic, one of the following occurs:

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

· 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.

To enable dropping unknown multicast data in a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Enable dropping unknown multicast data.	igmp-snooping drop-unknown	Disabled by default

NOTE:

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

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.

To configure IGMP report suppression:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Enable IGMP report suppression.	report-aggregation	Enabled by default

CAUTION:

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

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

To limit the number of multicast programs on-demand available to users, and to regulate traffic on the port, you can configure the maximum number of multicast groups that a port can join.

To set the maximum number of multicast groups that a port can join:

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

NOTE:

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

Configuring multicast group replacement

For some special reasons, the number of multicast groups that can be joined on the current switch or port might 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:

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

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

Configuring multicast group replacement globally

To configure multicast group replacement globally:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter IGMP-snooping view.	igmp-snooping	N/A
3. Enable multicast group replacement.	overflow-replace [ vlan vlan-list ]	Disabled by default

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

To configure multicast group replacement on a port or a group of ports:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view, or enter port group view.	· Enter Layer 2 Ethernet interface view or Layer 2 aggregate interface view: interface interface-type interface-number · Enter port group view: port-group manual port-group-name	Use either approach.
3. Enable multicast group replacement.	igmp-snooping overflow-replace [ vlan vlan-list ]	Disabled by default.

CAUTION:

· Be sure to configure the maximum number of multicast groups that a port can join to a value other than the default one (see “Configuring IGMP report suppression“) before enabling multicast group replacement. Otherwise, the multicast group replacement function cannot take effect.

· Static multicast groups cannot be replaced.

Enabling the IGMP snooping host tracking function

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

Enabling the IGMP snooping host tracking function globally

To enable the IGMP snooping host tracking function globally:

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

Enabling the IGMP snooping host tracking function in a VLAN

To enable the IGMP snooping host tracking function in a VLAN:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter VLAN view.	vlan vlan-id	N/A
3. Enable the IGMP snooping host tracking function in the VLAN.	igmp-snooping host-tracking	Disabled by default.

Displaying and maintaining IGMP snooping

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

IGMP snooping configuration examples

NOTE:

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

Group policy and simulated joining configuration example

Network requirements

As shown in Figure 4, Router A connects to the multicast source through GigabitEthernet 3/0/2 and to Switch A through GigabitEthernet 3/0/1. IGMPv2 runs on Router A, IGMPv2 snooping runs on Device A, and Router A acts as the IGMP querier on the subnet.

The receivers, Host A and Host B can receive multicast traffic addressed to multicast group 224.1.1.1 only. Multicast data for group 224.1.1.1 can be forwarded through GigabitEthernet 3/0/3 and GigabitEthernet 3/0/4 of Device A even if Host A and Host B accidentally, temporarily stop receiving multicast data, and that Device A drops unknown multicast data and does not broadcast the data to the VLAN where Device A resides.

Figure 4 Network diagram

Configuration procedure

1. Configure IP addresses:

Configure an IP address and subnet mask for each interface as per Figure 4. (Details not shown)

2. Configure Router A:

# Enable IP multicast routing, enable PIM-DM on each interface, and enable IGMP on GigabitEthernet 3/0/1.

<RouterA> system-view

[RouterA] multicast routing-enable

[RouterA] interface GigabitEthernet 3/0/1

[RouterA-GigabitEthernet3/0/1] igmp enable

[RouterA-GigabitEthernet3/0/1] pim dm

[RouterA-GigabitEthernet3/0/1] quit

[RouterA] interface GigabitEthernet 3/0/2

[RouterA-GigabitEthernet3/0/2] pim dm

[RouterA-GigabitEthernet3/0/2] quit

3. Configure Device A:

# Enable IGMP snooping globally.

<DeviceA> system-view

[DeviceA] igmp-snooping

[DeviceA-igmp-snooping] quit

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

[DeviceA] vlan 100

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

[DeviceA-vlan100] igmp-snooping enable

[DeviceA-vlan100] igmp-snooping drop-unknown

[DeviceA-vlan100] quit

# Configure a multicast group filter so that the hosts in VLAN 100 can join only the multicast group 224.1.1.1.

[DeviceA] acl number 2001

[DeviceA-acl-basic-2001] rule permit source 224.1.1.1 0

[DeviceA-acl-basic-2001] quit

[DeviceA] igmp-snooping

[DeviceA-igmp-snooping] group-policy 2001 vlan 100

[DeviceA-igmp-snooping] quit

# Configure GigabitEthernet 3/0/3 and GigabitEthernet 3/0/4 as simulated hosts for multicast group 224.1.1.1.

[DeviceA] interface GigabitEthernet 3/0/3

[DeviceA-GigabitEthernet3/0/3] igmp-snooping host-join 224.1.1.1 vlan 100

[DeviceA-GigabitEthernet3/0/3] quit

[DeviceA] interface GigabitEthernet 3/0/4

[DeviceA-GigabitEthernet3/0/4] igmp-snooping host-join 224.1.1.1 vlan 100

[DeviceA-GigabitEthernet3/0/4] quit

4. Verify the configuration:

# Display detailed IGMP snooping groups information in VLAN 100 on Device A.

[DeviceA] 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, C-Copy port, P-PIM port

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

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

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

GE3/0/1 (D)

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

IP group address:224.1.1.1

(0.0.0.0, 224.1.1.1):

Attribute: Host Port

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

GE3/0/3 (D)

GE3/0/4 (D)

MAC group(s):

MAC group address:0100-5e01-0101

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

GE3/0/3

GE3/0/4

The output shows that GigabitEthernet 3/0/3 and GigabitEthernet 3/0/4 of Device A has joined multicast group 224.1.1.1.

Static port configuration example

Network requirements

As shown in Figure 5, Router A connects to a multicast source (Source) through GigabitEthernet 3/0/2, and to Device A through GigabitEthernet 3/0/1. IGMPv2 runs on Router A, and IGMPv2 snooping runs on Device A, Device B and Device C. Router A acts as the IGMP querier.

Host A and host C are permanent receivers of multicast group 224.1.1.1. GigabitEthernet 3/0/3 and GigabitEthernet 3/0/5 on Device C are required to be configured as static member ports for multicast group 224.1.1.1 to enhance the reliability of multicast traffic transmission.

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

NOTE:

· If no static router port is configured, when the path of Device A—Device B—Device 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 Device A—Device C. Namely multicast delivery will be interrupted during this process.

· For more information about the Spanning Tree Protocol (STP), see Layer 2—LAN Switching Configuration Guide.

Figure 5 Network diagram

Configuration procedure

1. Configure IP addresses:

Configure an IP address and subnet mask for each interface as per Figure 5. (Details not shown)

2. Configure Router A:

# Enable IP multicast routing, enable PIM-DM on each interface, and enable IGMP on GigabitEthernet 3/0/1.

<RouterA> system-view

[RouterA] multicast routing-enable

[RouterA] interface GigabitEthernet 3/0/1

[RouterA-GigabitEthernet3/0/1] igmp enable

[RouterA-GigabitEthernet3/0/1] pim dm

[RouterA-GigabitEthernet3/0/1] quit

[RouterA] interface GigabitEthernet 3/0/2

[RouterA-GigabitEthernet3/0/2] pim dm

[RouterA-GigabitEthernet3/0/2] quit

3. Configure Device A:

# Enable IGMP snooping globally.

<DeviceA> system-view

[DeviceA] igmp-snooping

[DeviceA-igmp-snooping] quit

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

[DeviceA] vlan 100

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

[DeviceA-vlan100] igmp-snooping enable

[DeviceA-vlan100] quit

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

[DeviceA] interface GigabitEthernet 3/0/3

[DeviceA-GigabitEthernet3/0/3] igmp-snooping static-router-port vlan 100

[DeviceA-GigabitEthernet3/0/3] quit

4. Configure Device B:

# Enable IGMP snooping globally.

<DeviceB> system-view

[DeviceB] igmp-snooping

[DeviceB-igmp-snooping] quit

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

[DeviceB] vlan 100

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

[DeviceB-vlan100] igmp-snooping enable

[DeviceB-vlan100] quit

5. Configure Device C:

# Enable IGMP snooping globally.

<DeviceC> system-view

[DeviceC] igmp-snooping

[DeviceC-igmp-snooping] quit

# Create VLAN 100, assign GigabitEthernet 3/0/1 through GigabitEthernet 3/0/5 to this VLAN, and enable IGMP snooping in the VLAN.

[DeviceC] vlan 100

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

[DeviceC-vlan100] igmp-snooping enable

[DeviceC-vlan100] quit

# Configure GigabitEthernet 3/0/3 and GigabitEthernet 3/0/5 as static member ports for multicast group 224.1.1.1.

[DeviceC] interface GigabitEthernet 3/0/3

[DeviceC-GigabitEthernet3/0/3] igmp-snooping static-group 224.1.1.1 vlan 100

[DeviceC-GigabitEthernet3/0/3] quit

[DeviceC] interface GigabitEthernet 3/0/5

[DeviceC-GigabitEthernet3/0/5] igmp-snooping static-group 224.1.1.1 vlan 100

[DeviceC-GigabitEthernet3/0/5] quit

6. Verify the configuration:

# Display detailed IGMP snooping group information in VLAN 100 on Device A.

[DeviceA] 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, C-Copy port, P-PIM port

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

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

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

GE3/0/1 (D)

GE3/0/3 (S)

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

IP group address:224.1.1.1

(0.0.0.0, 224.1.1.1):

Attribute: Host Port

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

GE3/0/2 (D)

MAC group(s):

MAC group address:0100-5e01-0101

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

GE3/0/2

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

# Display detailed IGMP snooping group information in VLAN 100 on Device C.

[DeviceC] 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, C-Copy port, P-PIM port

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

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

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

GE3/0/2 (D)

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

IP group address:224.1.1.1

(0.0.0.0, 224.1.1.1):

Attribute: Host Port

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

GE3/0/3 (S)

GE3/0/5 (S)

MAC group(s):

MAC group address:0100-5e01-0101

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

GE3/0/3

GE3/0/5

The output shows that GigabitEthernet 3/0/3 and GigabitEthernet 3/0/5 on Device C have become static member ports for multicast group 224.1.1.1.

IGMP snooping querier configuration example

Network requirements

As shown in Figure 6, in a Layer 2–only network environment, two multicast sources Source 1 and Source 2 send multicast data to multicast groups 224.1.1.1 and 225.1.1.1 respectively, Host A and Host C are receivers of multicast group 224.1.1.1, and Host B and Host D are receivers of multicast group 225.1.1.1. All the receivers are running IGMPv2, and all the devices need to run IGMPv2 snooping. Device A, which is close to the multicast sources, is chosen as the IGMP snooping querier.

To prevent flooding of unknown multicast traffic within the VLAN, be sure to configure all the devices to drop unknown multicast data packets. Because a switch does not enlist a port that has heard an IGMP query with a source IP address of 0.0.0.0 (default) as a dynamic router port, configure a non-all-zero IP address as the source IP address of IGMP queries to ensure normal creation of Layer 2 multicast forwarding entries.

Figure 6 Network diagram

Configuration procedure

1. Configure Device A:

# Enable IGMP snooping globally.

<DeviceA> system-view

[DeviceA] igmp-snooping

[DeviceA-igmp-snooping] quit

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

[DeviceA] vlan 100

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

# Enable IGMP snooping and the function of dropping unknown multicast traffic in VLAN 100.

[DeviceA-vlan100] igmp-snooping enable

[DeviceA-vlan100] igmp-snooping drop-unknown

# Enable the IGMP snooping querier function in VLAN 100

[DeviceA-vlan100] igmp-snooping querier

# Set the source IP address of IGMP general queries and group-specific queries to 192.168.1.1 in VLAN 100.

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

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

[DeviceA-vlan100] quit

2. Configure Device B:

# Enable IGMP snooping globally.

<DeviceB> system-view

[DeviceB] igmp-snooping

[DeviceB-igmp-snooping] quit

# Create VLAN 100, and assign GigabitEthernet 3/0/1 through GigabitEthernet 3/0/4 to the VLAN.

[DeviceB] vlan 100

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

# Enable IGMP snooping and the function of dropping unknown multicast traffic in VLAN 100.

[DeviceB-vlan100] igmp-snooping enable

[DeviceB-vlan100] igmp-snooping drop-unknown

[DeviceB-vlan100] quit

Configurations on Device C and Device D are similar to the configuration on Device B.

3. Verify the configuration:

After the IGMP snooping querier starts to work, all the devices but the querier can receive IGMP general queries.

# Display the IGMP message statistics on Device B.

[DeviceB] display igmp-snooping statistics

Received IGMP general queries:3.

Received IGMPv1 reports:0.

Received IGMPv2 reports:12.

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.

IGMP snooping proxying configuration example

Network requirements

As shown in Figure 7, Router A connects to a multicast source through port GigabitEthernet 3/1/2, and to Switch A through port GigabitEthernet 3/1/1. Router A runs IGMPv2 and Switch A runs IGMPv2 snooping. Router A serves as an IGMP querier.

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

Figure 7 Network diagram

Configuration procedure

1. Configure IP addresses for interfaces:

Configure an IP address and subnet mask for each interface as per Figure 7. The configuration steps are omitted here.

2. Configure Router A:

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

<RouterA> system-view

[RouterA] multicast routing-enable

[RouterA] interface GigabitEthernet 3/1/1

[RouterA-GigabitEthernet3/1/1] igmp enable

[RouterA-GigabitEthernet3/1/1] pim dm

[RouterA-GigabitEthernet3/1/1] quit

[RouterA] interface GigabitEthernet 3/1/2

[RouterA-GigabitEthernet3/1/2] pim dm

[RouterA-GigabitEthernet3/1/2] quit

3. Configure Switch A:

# Enable IGMP snooping globally.

<SwitchA> system-view

[SwitchA] igmp-snooping

[SwitchA-igmp-snooping] quit

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

[SwitchA] vlan 100

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

[SwitchA-vlan100] igmp-snooping enable

[SwitchA-vlan100] igmp-snooping proxying enable

[SwitchA-vlan100] quit

4. Verify the configuration:

After the configuration is completed, Host A and Host B send IGMP join messages for group 224.1.1.1. Receiving the messages, Switch A sends a join message for the group out port GigabitEthernet 3/0/1 (a router port) to Router A.

# Display information about IGMP snooping groups on Switch A.

[SwitchA] display igmp-snooping group

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

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

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

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

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

GE3/0/1 (D)

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

IP group address:224.1.1.1

(0.0.0.0, 224.1.1.1):

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

GE3/0/3 (D)

GE3/0/4 (D)

MAC group(s):

MAC group address:0100-5e01-0101

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

GE3/0/3

GE3/0/4

# Display information about IGMP multicast groups on Router A.

[RouterA] display igmp group

Total 1 IGMP Group(s).

Interface group report information of VPN-Instance: public net

GigabitEthernet3/1/1(10.1.1.1):

Total 1 IGMP Group reported

Group Address Last Reporter Uptime Expires

224.1.1.1 0.0.0.0 00:00:06 00:02:04

When Host A leaves the multicast group, it sends an IGMP leave message to Switch A. Receiving the message, Switch A removes port GigabitEthernet 3/0/4 from the member port list of the forwarding entry for the group; however, it does not remove the group or forward the leave message to Router A because Host B is still in the group.

# Display information about IGMP snooping groups on Switch A.

[SwitchA] display igmp-snooping group

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

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

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

Vlan(id):100.

Total 1 IP Group(s).

Total 1 IP Source(s).

Total 1 MAC Group(s).

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

GE3/0/1 (D)

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

IP group address:224.1.1.1

(0.0.0.0, 224.1.1.1):

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

GE3/0/3 (D)

MAC group(s):

MAC group address:0100-5e01-0101

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

GE3/0/3

Troubleshooting IGMP snooping

Layer 2 multicast forwarding cannot function

Symptom

Layer 2 multicast forwarding cannot function.

Analysis

IGMP snooping is not enabled.

Solution

1. Use 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 the igmp-snooping enable command to enable IGMP snooping in VLAN view.

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

Configured multicast group policy fails to take effect

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.

Analysis

· The ACL rule is incorrectly configured.

· The multicast group policy is not correctly applied.

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

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.

Appendix

Processing of multicast protocol messages

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

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

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

¡ Maintains dynamic router ports according to PIM hello packets

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

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

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

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

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

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

NOTE:

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

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

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

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

08-IP Multicast Configuration Guide

IGMP snooping related ports

Aging timers for dynamic ports in IGMP snooping and related messages and actions

When receiving a general query

When receiving a membership report

When receiving a leave message

Configuring basic IGMP snooping functions

Enabling IGMP snooping

Configuring the version of IGMP snooping

Configuring the maximum number of global IGMP forwarding entries

Configuring aging timers for dynamic ports

Configuring aging timers for dynamic ports globally

Configuring aging timers for dynamic ports in a VLAN

Configuring simulated joining

Configuring fast-leave processing

Configuring fast-leave processing globally

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

Configuring IGMP snooping querier

Enabling IGMP snooping querier

Configuring IGMP queries and responses

Configuring IGMP queries and responses globally

Configuring IGMP queries and responses in a VLAN

Configuring source IP address of IGMP queries

Configuring IGMP snooping proxying

Configuring a multicast group filter

Configuring a multicast group filter globally

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

Enabling dropping unknown multicast data

Configuring multicast group replacement

Configuring multicast group replacement globally

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

Enabling the IGMP snooping host tracking function

Enabling the IGMP snooping host tracking function globally

Enabling the IGMP snooping host tracking function in a VLAN

IGMP snooping configuration examples

Group policy and simulated joining configuration example

Network requirements

Configuration procedure

Static port configuration example

Network requirements

Configuration procedure

IGMP snooping querier configuration example

Network requirements

Configuration procedure

Network requirements

Configuration procedure

Layer 2 multicast forwarding cannot function

Symptom

Analysis

Solution

Symptom

Analysis

Solution

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