User`s manual

NPort S8000 Series Switch Featured Functions
6-33
Network with multicast filtering
Hosts only receive dedicated traffic from other hosts belonging to the same group
Multicast Filtering and Moxa Switching Device Server
The NPort S8000 has three ways to achieve multicast filtering: IGMP (Internet Group Management Protocol)
Snooping, GMRP (GARP Multicast Registration Protocol), and adding a static multicast MAC manually to filter
multicast traffic automatically
IGMP Multicast Filtering
IGMP is used by IP-supporting network devices to register hosts with multicast groups. It can be used on all
LANs and VLANs that contain a multicast capable IP router, and on other network devices that support
multicast filtering. IGMP works as follows:
The IP router (or querier) periodically sends query packets to all end-stations on the LANs or VLANs that are
connected to it. For networks with more than one IP router, the router with the lowest IP address is the querier.
A switch with IP address lower than the IP address of any other IGMP queriers connected to the LAN or VLAN
can become the IGMP querier.
When an IP host receives a query packet, it sends a report packet back that identifies the multicast group that
the end-station would like to join.
When the report packet arrives at a port on a switch with IGMP Snooping enabled, the switch knows that the
port should forward traffic for the multicast group, and then proceeds to forward the packet to the router.
When the router receives the report packet, it registers that the LAN or VLAN requires traffic for the multicast
groups.
When the router forwards traffic for the multicast group to the LAN or VLAN, the switches only forward the
traffic to ports that received a report packet.