Moxa Technologies EDS-726 user manual Multicast Filtering, Network without multicast filtering

EDS-726 Series User’s Manual Featured Functions

industrial automation protocols, such as Allen-Bradley, EtherNet/IP, Siemens Profibus, and Foundation Fieldbus HSE (High Speed Ethernet), use multicast. These industrial Ethernet protocols use publisher/subscriber communications models by multicasting packets that could flood a network with heavy traffic. IGMP Snooping is used to prune multicast traffic so that it travels only to those end destinations that require the traffic, reducing the amount of traffic on the Ethernet LAN.

Multicast Filtering

Multicast filtering ensures that only end-stations that have joined certain groups receive multicast traffic. With multicast filtering, network devices only forward multicast traffic to the ports that are connected to registered end-stations. The following two figures illustrate how a network behaves without multicast filtering, and with multicast filtering.

Network without multicast filtering

Group 1 Multicast Stream				Group 2 Multicast Stream
		Serial ports
	Console LAN	1 2 3	4 5 6 7 8 9 10 11 12 13 14 15 16

IGMP Group2 IGMP Group1 IGMP Group2 IGMP Group1

All hosts receive the multicast traffic, even if they don’t need it.

Network with multicast filtering

Group 1 Multicast Stream Group 2 Multicast Stream

IGMP Group2 IGMP Group1 IGMP Group2 IGMP Group1

Hosts only receive dedicated traffic from other hosts belonging to the same group.

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