Licensing Requirements and Limitations for IGMP Snooping

Involved Network Elements

An IPv4 multicast network consists of the following network elements:

Multicast source

A device that sends multicast data to receiver hosts. For example, a video server is a multicast source.
IPv4 Protocol Independent Multicast (PIM) device

A device that uses the IPv4 PIM protocol to generate and maintain multicast routing entries and forwards multicast data based on multicast routing entries. On an IPv4 multicast network, all Layer 3 devices must run IPv4 PIM; otherwise, multicast forwarding paths cannot be established.
Multicast Source Discovery Protocol (MSDP) device

A device that forwards multicast data from one PIM network to another. For example, if multicast data needs to be transmitted between two autonomous systems (ASs), the devices at the border of the ASs must run the MSDP protocol.
Multicast VPN device

Multicast VPN enables multicast data of a private network to be transmitted over a public network. Multicast VPN devices are used on VPN networks. For example, if two sites of a VPN network need to exchange multicast data across a public network, multicast VPN needs to be configured on the PE devices.
IGMP querier

A device that exchanges IGMP messages with receiver hosts to create and maintain group memberships. On a multicast network, Layer 3 devices connected to network segments of receivers must run the IGMP protocol or be configured with static IGMP groups. Otherwise, upstream PIM devices cannot know the multicast groups that users want to join, and therefore cannot establish multicast forwarding paths.
IGMP snooping device

A device that listens to IGMP messages exchanged between upstream Layer 3 multicast devices and receiver hosts to create and maintain Layer 2 multicast forwarding entries, which are used for accurate multicast data forwarding on a Layer 2 network. To prevent broadcasting of multicast packets on a Layer 2 network and conserve network bandwidth, it is recommended that you configure IGMP snooping on Layer 2 devices.
Receiver

A multicast user that receives multicast data. A receiver can be a PC, a set top box, or any device with multicast client installed.

The "IGMP Snooping Configuration" section describes how to configure IGMP snooping on a Layer 2 device.

License Requirements

IGMP snooping is a basic feature of a switch and is not under license control.

Feature Support in V200R019C10

All models of S2720, S5700, and S6700 series switches support VLAN-based IGMP Snooping.

Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731S-H, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730S-H, and S6730-H support VSI-based IGMP Snooping.

For details about software mappings, visit Hardware Query Tool and search for the desired product model.

Feature Limitations

When configuring IGMP snooping, pay attention to the following points:

Because IGMP snooping is a Layer 2 multicast feature, all the IGMP snooping configurations on interfaces mentioned in this chapter are performed on Layer 2 physical interfaces, including Eth-Trunk interfaces.
For the S5735-L, S5735S-L, S5735S-L-M, S5735-S, S5735-S-I, and S5735S-S, the multicast functions (both Layer 2 and Layer 3 multicast functions) conflict with the flow control function.
The following constraints apply to VSI-based IGMP snooping:
- VSI-based IGMP snooping depends on the MPLS feature.
  
  Among S5720-EI switches running V200R009C00 and later versions, only some switches support the MPLS feature. Run the display device capability command on the switch to check the switch's software and hardware capabilities. The switch supports the MPLS feature only when chips also support the MPLS feature.
- The VSI-based IGMP snooping feature is applicable only to Martini VPLS networking.
- The switch supports only MAC address-based multicast forwarding when VSI-based IGMP snooping is configured.
- When configuring VSI-based IGMP snooping, make sure that an AC-side interface on the VPLS network cannot be a physical Ethernet interface that has been switched to Layer 3 mode using the undo portswitch command.
Layer 2 multicast can be configured for the dynamic VLAN delivered in NAC authentication only in V200R011C00 and later versions, but not in versions earlier than V200R011C00.
If a switch running IGMP snooping receives IGMPv1 or IGMPv2 Report messages with SSM group addresses (default range: 232.0.0.0/8), the switch does not create Layer 2 multicast forwarding entries.
On a ring network running IGMP snooping, if the downstream port of a device is configured as a static router port, downstream ports of all devices on the ring network must be configured as static router ports. Otherwise, multicast traffic cannot be forwarded normally if the Layer 2 network topology changes. Therefore, it is not recommended to configure downstream ports as static router ports.
On the S5720-HI, learning of multicast group memberships can be configured on a WLAN-ESS interface from versions of V200R005 to V200R008.
If both Layer 2 and Layer 3 multicast services are required in a VLAN, enable IGMP and PIM (IPv4) on the corresponding VLANIF interface first, and then enable IGMP snooping in the VLAN. If IGMP snooping is enabled in the VLAN first, IGMP and PIM (IPv4) cannot be enabled on the VLANIF interface.

On a switch running IGMP snooping, multicast flows that are not requested by users are considered unknown multicast flows. Multicast flows are considered unknown if they do not match any entry in the multicast forwarding table or if they match multicast forwarding entries with an empty outbound interface list. These flows are not requested by users. The default method that a switch uses to process unknown IPv4 multicast flows depends on whether Layer 2 multicast is enabled and which Layer 2 multicast forwarding mode is used:

If Layer 2 multicast is not enabled on a switch, the switch broadcasts unknown multicast flows.

If Layer 2 multicast is enabled on a switch, the switch processes unknown multicast flows in different ways.

**Table 1** Method of processing unknown IPv4 multicast flows after Layer 2 multicast is enabled
Version	Processing Method
V200R011 and earlier versions	On the S2700-EI, S2720-EI, S5700-SI, S2750-EI, S5720-LI, S5720S-LI, S5700S-LI, S5700-LI, S5710-X-LI, S5720S-SI, S5720-SI, S5720I-SI, S5730-SI, S5730S-EI, S6720-LI, S6720S-LI, S6720-SI, and S6720S-SI, they broadcast unknown multicast flows in the corresponding VLAN. On other switch models, they broadcast unknown multicast flows in the corresponding VLAN in MAC address-based forwarding mode and drop unknown multicast flows in IP address-based forwarding mode.
V200R012C00	On the S2720-EI, S2750-EI, S5700S-LI, S5700-LI, and S5710-X-LI, they broadcast unknown multicast flows in the corresponding VLAN. On other switch models, they broadcast unknown multicast flows in the corresponding VLAN in MAC address-based forwarding mode and drop unknown multicast flows in IP address-based forwarding mode.
V200R013 and later versions	On the S2720-EI, they broadcast unknown multicast flows in the corresponding VLAN. On other switch models, they broadcast unknown multicast flows in the corresponding VLAN in MAC address-based forwarding mode and drop unknown multicast flows in IP address-based forwarding mode.

To prevent broadcast of unknown multicast flows, run the multicast drop-unknown command in a VLAN or run the unknown-frame multicast drop command in a VSI to configure a switch to drop unknown multicast flows.

For the S5735-L, S5735S-L, S5735S-L-M, S5735-S, S5735-S-I, and S5735S-S, if MAC address-based forwarding is configured as the Layer 2 multicast forwarding mode and the multicast drop-unknown command is executed, unknown multicast packets destined for the following reserved network segments and IP address cannot be dropped: 239.0.0.0/8, 224.0.0.0/24, 224.0.1.0/24, FF0X:0:0:0:0:0:0:0/96, FF0X::DB8:0:0/96, and the IPv6 address with the last 32 bits being 0000:00XX. To drop such unknown multicast packets, configure a traffic policy.