Installation manual

3-244
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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 Query (page 3-245) 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 3-249). 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 3-249). 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 3-251).