Moxa EDR-810-VPN-2GSFP [39/139] Multicast filtering and moxa s industrial secure routers

Industrial Secure Router User's Manual EDR-810 Series Features and Functions

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Multicast transmission makes more sense and is more efficient than unicast transmission for some applications.

For example, multicasts are often used for video-conferencing, since high volumes of traffic must be sent to

several end-stations at the same time, but where broadcasting the traffic to all end-stations would cause a

substantial reduction in network performance. Furthermore, several 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

All hosts receive the multicast

traffic, even if they don’t need it.

Network with multicast filtering

Hosts only receive dedicated

traffic from other hosts

belonging to the same group.

Multicast Filtering and Moxa’s Industrial Secure Routers

The Moxa industrial secure router has two ways to achieve multicast filtering: IGMP (Internet Group

Management Protocol) Snooping and adding a static multicast MAC manually to filter multicast traffic

automatically.