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Multicast Filtering
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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 all sources except for those specified. In this case, traffic is filtered
from sources in the Exclude list, and forwarded from all other available sources.
Notes: 1.
When the switch is configured to use IGMPv3 snooping, the snooping
version may be downgraded to version 2 or version 1, depending on the
version of the IGMP query packets detected on each VLAN.
2. IGMP snooping will not function unless a multicast router port is enabled on
the switch. This can be accomplished in one of two ways. A static router port
can be manually configured (see “Specifying Static Interfaces for a Multicast
Router” on page 3-217). Using this method, the router port is never timed
out, and will continue to function until explicitly removed. The other method
relies on the switch to dynamically create multicast routing ports whenever
multicast routing protocol packets or IGMP query packets are detected on a
port.
3. A maximum of up to 255 multicast entries can be maintained for IGMP
snooping, and 255 entries for Multicast Routing, when both of these features
are enabled. If the table’s capacity is exceeded, the IGMPv3 snooping will
not support multicast source filtering, but will forward multicast traffic from all
relevant sources to the requesting hosts.
Static IGMP Router Interface – If IGMP snooping cannot locate the IGMP querier,
you can manually designate a known IGMP querier (i.e., a multicast router/switch)
connected over the network to an interface on your switch (page 3-217). This
interface will then join all the current multicast groups supported by the attached
router/switch to ensure that multicast traffic is passed to all appropriate interfaces
within the switch.
Static IGMP Host Interface – For multicast applications that you need to control
more carefully, you can manually assign a multicast service to specific interfaces on
the switch (page 3-219).
Configuring IGMP Snooping and Query Parameters
You can configure the switch to forward multicast traffic intelligently. Based on the
IGMP query and report messages, the switch forwards traffic only to the ports that
request multicast traffic. This prevents the switch from broadcasting the traffic to all
ports and possibly disrupting network performance.
Command Usage
• IGMP Snooping – This switch can passively snoop on IGMP Query and Report
packets transferred between IP multicast routers/switches and IP multicast host
groups to identify the IP multicast group members. It simply monitors the IGMP
packets passing through it, picks out the group registration information, and
configures the multicast filters accordingly.
Note:
Unknown multicast traffic is flooded to all ports in the VLAN for several seconds
when first received. If a multicast router port exists on the VLAN, the traffic will be
filtered by subjecting it to IGMP snooping. If no router port exists on the VLAN or