TN-5516/5518 User’s Manual Featured Functions
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Multicast Filtering and Moxa’s ToughNet switches
The TN-5500 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.
IGMP Snooping Enhanced Mode
Snooping Enhanced Mode allows your switch to forward multicast packets to the TN-5500’s
member port only. If you disable Enhanced Mode, data streams will run to the querier port as well
as the member port.
Query Mode
Query mode allows the TN-5500 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 TN-5500 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
TN-5500 is compatible with any device that conforms to the IGMP v2 and IGMP v3 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.
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