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 ExtremeXOS 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.

IETF standards require that a router accept and process IGMPv2 and IGMPv3 packets only when the router-alert option is set in received IGMP packets.

By default, the ExtremeXOS software receives and processes all IGMP packets, regardless of the setting of the router-alert option within a packet. When the switch will be used with third-party switches that expect IETF compliant behavior, use the following command to manage this feature:

configure igmp router-alert receive-required [on | off] {{vlan} vlan_name}

configure igmp router-alert transmit [on | off] {{vlan} vlan_name}

By default, IGMP report/leave message for the local multicast address (224.0.0.x/24 groups) will always have the router-alert option set, regardless of IGMP router-alert transmit option (on and off) setting by the user.

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.



The ExtremeXOS software supports IGMPv3 source include mode filtering, but it does not support IGMPv3 specific source exclude mode filtering.