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IGMP Snooping

IGMP specifies how a host can register to a router to receive specific multicast traffic. Configure the switch to use IGMP snooping in subnets that receive IGMP queries from either IGMP or the IGMP snooping querier. IGMP snooping constrains multicast traffic at Layer 2 by configuring Layer 2 LAN ports dynamically to forward multicast traffic only to those ports that want to receive it. IGMP is a standard defined in RFC1112 for IGMPv1 and in RFC2236 for IGMPv2.

To configure IGMP snooping:

  1. Select Switching > Multicast > IGMP Snooping. A screen similar to the following displays.
  2. .

    Figure 4-17

  3. Select a radio button to enable or disable IGMP snooping:
    • Disable. IGMP snooping is disabled. This is the default setting.
    • Enable. IGMP snooping is enabled.
    • When you enable IGMP snooping, the screen expands to display fields in which you can specify how IGMP leave packets are processed. See 4..

  4. Select a radio button to enable or disable blocking of unknown multicast addresses:
    • Disable. Blocking of unknown multicast addresses is disabled. This is the default setting.
    • Enable. Blocking of unknown multicast addresses is enabled.
  5. When you enable IGMP snooping, the screen expands to display fields in which you can specify how IGMP leave packets are processed. In addition, dynamic multicast information is displayed. Select a radio button to specify how IGMP leave packets are processed:
    • Disable. Specifies that an incoming IGMP leave packet is forwarded to the multicast router, that is, the incoming IGMP leave packet is not blocked. When the multicast router receives the packet, it closes the channel.
    • Enable. Specifies that an incoming IGMP leave packet is filtered (also referred to as blocked) and, therefore, not forwarded to the multicast router.This is the default setting.
    • Under Dynamic Multicast, the following information is displayed:

    • ID. Shows the dynamic multicast entry ID.
    • VID. Shows the VLAN ID.
    • Multicast Entry. Shows the Layer 2 group multicast address.
    • Port Members. Shows the membership that is associated with the group.
  6. Click Apply to confirm any settings changes.

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