In FortiSwitchOS 7.6,IGMP snooping proxyis an enhancement to standard IGMP snooping that optimizes multicast control-plane traffic between hosts, switches, and the upstream IGMP querier. Its primary purpose is toreduce the number of IGMP membership reportsthat the querier must process, thereby improving scalability and efficiency in multicast-enabled networks.
Without an IGMP snooping proxy, every multicast receiver on a VLAN independently sends IGMP membership reports to the querier. In environments with many hosts subscribing to the same multicast groups, this behavior can generate a large volume of redundant IGMP reports, unnecessarily increasing control-plane load on both the querier and intermediate network devices.
When the IGMP snooping proxy feature is enabled, the FortiSwitch acts as anIGMP proxy agenton behalf of hosts within the VLAN. The switch tracks multicast group membership locally andsuppresses individual IGMP reports from downstream hosts. Instead, the FortiSwitch forwards an IGMP report upstreamonly when the first host joins a multicast group. Likewise, when hosts leave the group, the switch sends an IGMP leave message or reportonly when the last remaining member leaves.
This aggregation mechanism dramatically reduces IGMP signaling traffic while preserving correct multicast forwarding behavior. Importantly, the switch does not alter IGMP packet types or convert them to broadcast or unicast traffic. It simply optimizes reporting behavior based on group membership state.
Therefore, the correct explanation is that IGMP snooping proxy reduces IGMP report processingby forwarding IGMP reports only when the first member joins and the last member leaves, makingOption Dthe correct and fully verified answer according to FortiSwitchOS 7.6 documentation.
