Contemporary Control Systems Compact Managed Switches Software Manual for Web Browser - Manual (Page 51)

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4.4.12 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 that are for multicast
groups and direct those packets to only the destination ports. These are ports which
have received IGMP “join” messages from devices that seek membership in specific
multicast groups. Figure 41 illustrates the Configure IGMP Snooping default screen
for an 8-port switch. (Screens for 16- and 24-port models would simply display more
ports.) The available 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 (secs) specifies how often querying occurs. This setting is
meaningless if the IGMP Query Function is disabled.
Multicast Filtering Age Out (secs) 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 41 — Configure IGMP Snooping for 8-port Models