LevelOne GTL-2690 - Manual (Page 283)

Multicast Filtering
15-2
15
Layer 2 IGMP (Snooping and Query)
IGMP Snooping and Query – If multicast routing is not supported on other switches
in your network, you can use IGMP Snooping and IGMP Query (page 15-3) to
monitor IGMP service requests passing between multicast clients and servers, and
dynamically configure the switch ports which need to forward multicast traffic.
When using IGMPv3 snooping, 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), and a channel indicates a flow for which the
hosts have requested service from a specific source.
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 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 15-7). 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 15-7). 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.