A: IGMP Snooping and IGMP Query are processes by which network switches listen to IGMP (Internet Group Management Protocol snooping), or multicast, conversations between network devices and then filter out unnecessary traffic.  IGMP Snooping is very important in order to ensure proper performance on networks with heavy multicast traffic, like those using Ethernet/IP.

All ORing’s managed switches feature IGMP snooping and IGMP query for use on Ethernet/IP networks.  When a switch without IGMP Snooping receives multicast messages, it floods all ports, potentially overloading end devices and other network switches.   However, a switch with IGMP Snooping can forward multicast messages to only the devices that request the traffic and are designed to handle it.

When an Ethernet/IP device wants to consume multicast data, it will transmit an IGMP join message.  These join messages are received by all IGMP Snooping switches and the switch "snoops" on the join messages as they pass in order to determine which ports will receive the multicast data.   This restricts the multicast data to only the ports-and connected end devices-that expect and can handle the traffic.

For IGMP Snooping to work properly, one or more switches or routers in the network must provide IGMP Query support.  The IGMP Querier will periodically ask each end device in the network which multicasts they wish to receive, refreshing the IGMP multicast/port associations.