Contemporary Control Systems Compact Managed Switches Software Manual for Console Access - Manual (Page 49)

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4.3.12 Configure IGMP Snooping
Traditionally, IP messages are either unicast or broadcast, but multicasting can deliver
messages to a select group of devices on the network. IGMP (Internet Group Multicast
Protocol) is a session-layer protocol for defining membership in a multicast group.
IGMP Group Destination Addresses (GDA) range from 224.0.0.0 to 239.255.255.255.
Managed switches from Contemporary Controls support IGMPv2 and can provide the
querier function in the event no router exists in the network. Our switches implement
the general query function in which members of all multicast groups report.
With IGMP Snooping, managed switches can recognize packets for multicast groups
and direct them to only the destination ports which have received IGMP “join” messages
from devices seeking membership in specific multicast groups. Figure 40 illustrates the
Configure IGMP Snooping screen (for an 8-port switch). The controls are listed below.
IGMP Snooping State enables or disables IGMP Snooping.
IGMP Querier Function allows the switch to initiate a query to discover multicast group
membership. Only one querier is allowed on a network at a time. If a query is
transmitted by a device with a lower IP address than this switch, this switch relinquishes
the role of querier to that device. If another LAN device is preferred for the query
function, then this option can be disabled.
IGMP Forwarding Map specifies the ports that will forward IGMP join or leave messages to
other querying devices. Disabling ports that do not connect to querying devices can
improve bandwidth.
IGMP Query Interval (in seconds) specifies how often querying occurs. This setting is
meaningless if the IGMP Query Function is disabled.
Multicast Filtering Age Out (in seconds) specifies how long the switch waits before
deleting an entry from its multicast group list. If no member of a group responds within
this time, the group is deemed inactive and removed from the list. This time should
exceed the Query Interval or else the entry may be deleted before another query occurs.
The switch can accommodate up to 100 multicast groups.
Figure 40 — Configure IGMP Snooping