Configuring Igmp Snooping; Igmp Snooping And Switch Stacks - Cisco Catalyst 2975 Software Configuration Manual

Configuring IGMP Snooping

The switch uses IGMP report suppression to forward only one IGMP report per multicast router query
to multicast devices. When IGMP router suppression is enabled (the default), the switch sends the first
IGMP report from all hosts for a group to all the multicast routers. The switch does not send the
remaining IGMP reports for the group to the multicast routers. This feature prevents duplicate reports
from being sent to the multicast devices.
If the multicast router query includes requests only for IGMPv1 and IGMPv2 reports, the switch
forwards only the first IGMPv1 or IGMPv2 report from all hosts for a group to all the multicast routers.
If the multicast router query also includes requests for IGMPv3 reports, the switch forwards all IGMPv1,
IGMPv2, and IGMPv3 reports for a group to the multicast devices.
If you disable IGMP report suppression, all IGMP reports are forwarded to the multicast routers. For
configuration steps, see the

IGMP Snooping and Switch Stacks

IGMP snooping functions across the switch stack; that is, IGMP control information from one switch is
distributed to all switches in the stack. (See
about switch stacks.) Regardless of the stack member through which IGMP multicast data enters the
stack, the data reaches the hosts that have registered for that group.
If a switch in the stack fails or is removed from the stack, only the members of the multicast group that
are on that switch will not receive the multicast data. All other members of a multicast group on other
switches in the stack continue to receive multicast data streams. However, multicast groups that are
common for both Layer 2 and Layer 3 (IP multicast routing) might take longer to converge if the stack
master is removed.
Configuring IGMP Snooping
IGMP snooping allows switches to examine IGMP packets and make forwarding decisions based on their
content. These sections contain this configuration information:
•
•
•
•
•
•
•
•
•
•
Catalyst 2975 Switch Software Configuration Guide
22-6
"Disabling IGMP Report Suppression" section on page
Default IGMP Snooping Configuration, page 22-7
Enabling or Disabling IGMP Snooping, page 22-7
Setting the Snooping Method, page 22-8
Configuring a Multicast Router Port, page 22-9
Configuring a Host Statically to Join a Group, page 22-10
Enabling IGMP Immediate Leave, page 22-10
Configuring the IGMP Leave Timer, page 22-11
Configuring TCN-Related Commands, page 22-12
Configuring the IGMP Snooping Querier, page 22-14
Disabling IGMP Report Suppression, page 22-15
Chapter 22
Chapter 6, "Managing Switch Stacks,"
Configuring IGMP Snooping and MVR
22-15.
for more information
OL-19720-02