ToughNet NAT Router User's Manual
TN-5916 Series Features and Functions
3-20
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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.
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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.
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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.
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When the router receives the report packet, it registers that the LAN or VLAN requires traffic for the
multicast groups.
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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.
IGMP version comparison
IGMP Version
Main Features
Reference
V1
a. Periodic query
RFC-1112
V2
Compatible with V1 and adds:
a. Group-specific query
b. Leave group messages
c. Resends specific queries to verify leave message was the last one in
the group
d. Querier election
RFC-2236
Static Multicast MAC
Some devices may only support multicast packets, but not support either IGMP Snooping. The Moxa ToughNet
NAT Router supports adding multicast groups manually to enable multicast filtering.
Enabling Multicast Filtering
Use the USB console or web interface to enable or disable IGMP Snooping and IGMP querying. If IGMP Snooping
is not enabled, then IP multicast traffic is always forwarded, flooding the network.
IGMP Snooping
IGMP Snooping provides the ability to prune multicast traffic so that it travels only to those end destinations
that require that traffic, thereby reducing the amount of traffic on the Ethernet LAN.
IGMP Snooping Settings
Enable IGMP Snooping (Global)
Setting
Description
Factory Default
Enable/Disable
Checkmark the Enable IGMP Snooping checkbox near the top of
the window to enable the IGMP Snooping function globally.
Disabled
Query Interval (sec)
Setting
Description
Factory Default
Numerical value, input
by the user
Sets the query interval of the Querier function globally. Valid
settings are from 20 to 600 seconds.
125 seconds
