Cisco IE 4000, Software Configuration Manual

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Configuring IGMP Snooping and MVR
Information About IGMP Snooping and MVR
Without Immediate Leave, when the switch receives an IGMP leave message from a subscriber on a receiver port, it
sends out an IGMP query on that port and waits for IGMP group membership reports. If no reports are received in a
configured time period, the receiver port is removed from multicast group membership. With Immediate Leave, an IGMP
query is not sent from the receiver port on which the IGMP leave was received. As soon as the leave message is received,
the receiver port is removed from multicast group membership, which speeds up leave latency. Enable the Immediate
Leave feature only on receiver ports to which a single receiver device is connected.
MVR eliminates the need to duplicate television-channel multicast traffic for subscribers in each VLAN. Multicast traffic
for all channels is only sent around the VLAN trunk once—only on the multicast VLAN. The IGMP leave and join messages
are in the VLAN to which the subscriber port is assigned. These messages dynamically register for streams of multicast
traffic in the multicast VLAN on the Layer 3 device. Switch B. The access layer switch, Switch A, modifies the forwarding
behavior to allow the traffic to be forwarded from the multicast VLAN to the subscriber port in a different VLAN,
selectively allowing traffic to cross between two VLANs.
IGMP reports are sent to the same IP multicast group address as the multicast data. The Switch A CPU must capture all
IGMP join and leave messages from receiver ports and forward them to the multicast VLAN of the source (uplink) port,
based on the MVR mode.
Default MVR Settings
MVR Configuration Guidelines and Limitations

Receiver ports can only be access ports; they cannot be trunk ports. Receiver ports on a switch can be in different
VLANs, but should not belong to the multicast VLAN.

The maximum number of multicast entries (MVR group addresses) that can be configured on a switch (that is, the
maximum number of television channels that can be received) is 256.

MVR multicast data received in the source VLAN and leaving from receiver ports has its time-to-live (TTL)
decremented by 1 in the switch.

Because MVR on the switch uses IP multicast addresses instead of MAC multicast addresses, aliased IP multicast
addresses are allowed on the switch. However, if the switch is interoperating with Catalyst 3550 or Catalyst 3500
XL switches, you should not configure IP addresses that alias between themselves or with the reserved IP multicast
addresses (in the range 224.0.0.xxx).

Do not configure MVR on private VLAN ports.

MVR is not supported when multicast routing is enabled on a switch. If you enable multicast routing and a multicast
routing protocol while MVR is enabled, MVR is disabled, and you receive a warning message. If you try to enable
MVR while multicast routing and a multicast routing protocol are enabled, the operation to enable MVR is cancelled,
and you receive an error message.

MVR can coexist with IGMP snooping on a switch.
Feature Default Setting
MVR Disabled globally and per interface
Multicast addresses None configured
Query response time 0.5 second
Multicast VLAN VLAN 1
Mode Compatible
Interface (per port) default Neither a receiver nor a source port
Immediate Leave Disabled on all ports