Consolidated Platform Configuration Guide, Cisco Ios Release 15.2(4)E (Catalyst 2960-X Switches - Cisco Catalyst 2960 series Configuration Manual

Information About IGMP Snooping and MVR
• MVR does not support IGMPv3 messages.
• The switch supports homogeneous stacking and mixed stacking. Mixed stacking is supported only with
Information About IGMP Snooping and MVR
IGMP Snooping
Layer 2 switches can use IGMP snooping to constrain the flooding of multicast traffic by dynamically
configuring Layer 2 interfaces so that multicast traffic is forwarded to only those interfaces associated with
IP multicast devices. As the name implies, IGMP snooping requires the LAN switch to snoop on the IGMP
transmissions between the host and the router and to keep track of multicast groups and member ports. When
the switch receives an IGMP report from a host for a particular multicast group, the switch adds the host port
number to the forwarding table entry; when it receives an IGMP Leave Group message from a host, it removes
the host port from the table entry. It also periodically deletes entries if it does not receive IGMP membership
reports from the multicast clients.
For more information on IP multicast and IGMP, see RFC 1112 and RFC 2236.
Note
The multicast router ) sends out periodic general queries to all VLANs. All hosts interested in this multicast
traffic send join requests and are added to the forwarding table entry. The switch creates one entry per VLAN
in the IGMP snooping IP multicast forwarding table for each group from which it receives an IGMP join
request.
The switch supports IP multicast group-based bridging, instead of MAC-addressed based groups. With
multicast MAC address-based groups, if an IP address being configured translates (aliases) to a previously
configured MAC address or to any reserved multicast MAC addresses (in the range 224.0.0.xxx), the command
fails. Because the switch uses IP multicast groups, there are no address aliasing issues.
The IP multicast groups learned through IGMP snooping are dynamic. However, you can statically configure
multicast groups by using the ip igmp snooping vlan vlan-id static ip_address interface interface-id global
configuration command. If you specify group membership for a multicast group address statically, your setting
supersedes any automatic manipulation by IGMP snooping. Multicast group membership lists can consist of
both user-defined and IGMP snooping-learned settings.
You can configure an IGMP snooping querier to support IGMP snooping in subnets without multicast interfaces
because the multicast traffic does not need to be routed.
If a port spanning-tree, a port group, or a VLAN ID change occurs, the IGMP snooping-learned multicast
groups from this port on the VLAN are deleted.
These sections describe IGMP snooping characteristics:
Related Topics
Configuring the IGMP Snooping Querier , on page 142
Prerequisites for IGMP Snooping, on page 115
Example: Setting the IGMP Snooping Querier Source Address, on page 162

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the Catalyst 2960-S switches. A homogenous stack can have up to eight stack members, while a mixed
stack can have up to four stack members. All switches in a switch stack must be running the LAN Base
image.