LevelOne GSW-4876 User Manual
Page 146
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HAPTER
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| Configuring the Switch
IGMP Snooping
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Once the table used to store multicast entries for IGMP snooping is
filled, no new entries are learned. If no router port is configured in the
attached VLAN, and Unregistered IPMC Flooding is disabled, any
subsequent multicast traffic not found in the table is dropped,
otherwise it is flooded throughout the VLAN.
◆
IGMP SSM Range - The Source-Specific Multicast Range allows SSM-
aware hosts and routers to run the SSM service model for groups in the
specified address range.
When using IGMPv3 snooping (see the Compatibility parameter under
"Configuring VLAN Settings for IGMP Snooping and Query"
), service
requests from IGMP Version 1, 2 or 3 hosts are all forwarded to the
upstream router as IGMPv3 reports. The primary enhancement
provided by IGMPv3 snooping is in keeping track of information about
the specific multicast sources which downstream IGMPv3 hosts have
requested or refused. The switch maintains information about both
multicast groups and channels, where a group indicates a multicast
flow for which the hosts have not requested a specific source (the only
option for IGMPv1 and v2 hosts unless statically configured on the
switch as described under
), and a channel
indicates a flow for which the hosts have requested service from a
specific source. For IGMPv1/v2 hosts, the source address of a channel
is always null (indicating that any source is acceptable), but for IGMPv3
hosts, it may include a specific address when requested.
Only IGMPv3 hosts can request service from a specific multicast source.
When downstream hosts request service from a specific source for a
multicast service, these sources are all placed in the Include list, and
traffic is forwarded to the hosts from each of these sources. IGMPv3
hosts may also request that service be forwarded from any source
except for those specified. In this case, traffic is filtered from sources in
the Exclude list, and forwarded from all other available sources.
◆
Leave Proxy Enabled - Suppresses leave messages unless received
from the last member port in the group. (Default: Disabled)
IGMP leave proxy suppresses all unnecessary IGMP leave messages so
that a non-querier switch forwards an IGMP leave packet only when the
last dynamic member port leaves a multicast group.
The leave-proxy feature does not function when a switch is set as the
querier. When the switch is a non-querier, the receiving port is not the
last dynamic member port in the group, the receiving port is not a
router port, and no IGMPv1 member port exists in the group, the switch
will generate and send a group-specific (GS) query to the member port
which received the leave message, and then start the last member
query timer for that port.
When the conditions in the preceding item all apply, except that the
receiving port is a router port, then the switch will not send a GS-query,
but will immediately start the last member query timer for that port.
Leave proxy is also included in the general proxy function described
below. Therefore if Leave Proxy Enabled is not selected, but Proxy
Enabled is selected, leave proxy will still be performed.