Cisco Catalyst 2960 Series, Configuration Manual

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Example: Setting the IGMP Snooping Querier Maximum Response Time, on page 162
Example: Setting the IGMP Snooping Querier Timeout, on page 163
Example: Setting the IGMP Snooping Querier Feature, on page 163
IGMP Versions
The switch supports IGMP version 1, IGMP version 2, and IGMP version 3. These versions are interoperable
on the switch. For example, if IGMP snooping is enabled and the querier's version is IGMPv2, and the switch
receives an IGMPv3 report from a host, then the switch can forward the IGMPv3 report to the multicast router.
An IGMPv3 switch can receive messages from and forward messages to a device running the Source Specific
Multicast (SSM) feature.
Related Topics
Restrictions for IGMP Snooping, on page 116
Joining a Multicast Group
When a host connected to the switch wants to join an IP multicast group and it is an IGMP version 2 client,
it sends an unsolicited IGMP join message, specifying the IP multicast group to join. Alternatively, when the
switch receives a general query from the router, it forwards the query to all ports in the VLAN. IGMP version
1 or version 2 hosts wanting to join the multicast group respond by sending a join message to the switch. The
switch CPU creates a multicast forwarding-table entry for the group if it is not already present. The CPU also
adds the interface where the join message was received to the forwarding-table entry. The host associated
with that interface receives multicast traffic for that multicast group.
Figure 4: Initial IGMP Join Message
Router A sends a general query to the switch, which forwards the query to ports 2 through 5, all of which are
members of the same VLAN. Host 1 wants to join multicast group 224.1.2.3 and multicasts an IGMP
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Information About IGMP Snooping and MVR