Moxa EDS-82810G [60/113] Multicast filtering and moxa etherdevice switch
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Moxa EDS-82810G [60/113] Multicast filtering and moxa etherdevice switch

Moxa EDS-82810G [60/113] Multicast filtering and moxa etherdevice switch
EDS-828 Series Featured Functions
3-47
Multicast Filtering and Moxa EtherDevice Switch
The EDS-828 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 (Internet Group Management Protocol)
Snooping Mode
Snooping Mode allows your switch to forward multicast packets only to the appropriate ports. The switch
“snoops” on exchanges between hosts and an IGMP device, such as a router, to find those ports that want to
join a multicast group, and then configures its filters accordingly.
Query Mode
Query mode allows the EDS-828 to work as the Querier if it has the lowest IP address on the subnetwork to
which it belongs. IGMP querying is enabled by default on the EDS-828 to help prevent interoperability issues
with some multicast routers that may not follow the lowest IP address election method. Enable query mode to
run multicast sessions on a network that does not contain IGMP routers (or queriers).
NOTE
The EDS
-828 is compatible with any device that conforms to the IGMP v2 device protocol.
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:
1. 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.
2. 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.
3. 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.
4. When the router receives the report packet, it registers that the LAN or VLAN requires traffic for the
multicast groups.
5. 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.
GMRP (GARP Multicast Registration Protocol)
The EDS-828 supports IEEE 802.1D-1998 GMRP (GARP Multicast Registration Protocol), which differs from
IGMP (Internet Group Management Protocol). GMRP is a MAC-based multicast management protocol, whereas
IGMP is IP-based. GMRP provides a mechanism that allows bridges and end stations to register or de-register
Group membership information dynamically. GMRP functions similarly to GVRP, except that GMRP registers
multicast addresses on ports. When a port receives a GMRP-join message, it will register the multicast
address to its database if the multicast address is not registered, and all the multicast packets with that
multicast address are able to be forwarded from this port. When a port receives a GMRP-leave message, it will
de-register the multicast address from its database, and all the multicast packets with this multicast address
are not able to be forwarded from this port.

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