Netgear XCM8806 Chassis User Manual - Page 733
IGMP Overview, IGMP Snooping
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NETGEAR 8800 User Manual IGMP Overview IGMP is a protocol used by an IP host to register its IP multicast group membership with a router. A host that intends to receive multicast packets destined for a particular multicast address registers as a member of that multicast address group. Periodically, the router queries the multicast group to see if the group is still in use. If the group is still active, a single IP host responds to the query, and group registration is maintained. IGMPv2 is enabled by default on the switch, and the XCM8800 software supports IGMPv3. However, the switch can be configured to disable the generation of periodic IGMP query packets. IGMP should be enabled when the switch is configured to perform IP multicast routing. IGMPv3, specified in RFC 3376, adds support for source filtering. Source filtering is the ability for a system to report interest in receiving packets only from specific source addresses (filter mode include) or from all sources except for specific addresses (filter mode exclude). IGMPv3 is designed to be interoperable with IGMPv1 and IGMPv2. Note: The XCM8800 software supports IGMPv3 source include mode filtering, but it does not support IGMPv3 specific source exclude mode filtering. The following sections provide information on IGMP features: • IGMP Snooping on page 733 • Static IGMP on page 734 • IGMP Snooping Filters on page 735 • Limiting the Number of Multicast Sessions on a Port on page 736 • Enabling and Disabling IGMP Snooping Fast Leave on page 736 • Using IGMP-SSM Mapping on page 736 IGMP Snooping IGMP snooping is a Layer 2 function of the switch; it does not require multicast routing to be enabled. In IGMP snooping, the Layer 2 switch keeps track of IGMP reports and only forwards multicast traffic to that part of the local network that requires it. IGMP snooping optimizes the use of network bandwidth and prevents multicast traffic from being flooded to parts of the local network that do not need it. The switch does not reduce any IP multicast traffic in the local multicast domain (224.0.0.x). IGMP snooping is enabled by default on all VLANs in the switch. If IGMP snooping is disabled on a VLAN, all IGMP and IP multicast traffic floods within the VLAN. IGMP snooping expects at least one device on every VLAN to periodically generate IGMP query messages. To enable or disable IGMP snooping, use the following commands: Chapter 27. Multicast Routing and Switching | 733
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