Cisco 3032 Software Configuration Manual page 619

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Configuring IGMP Snooping and MVR

switch to join the appropriate multicast. If the IGMP report matches one of the configured IP multicast

group addresses, the switch CPU modifies the hardware address table to include this receiver port and

VLAN as a forwarding destination of the specified multicast stream when it is received from the

multicast VLAN. Uplink ports that send and receive multicast data to and from the multicast VLAN are

called MVR source ports.

Multicast VLAN

When the subscriber changes channels or stops the multicast stream, the server sends an IGMP leave

message for the multicast stream. The switch CPU sends a MAC-based general query through the

receiver port VLAN. If there is another device in the VLAN still subscribing to this group, that device

must respond within the maximum response time specified in the query. If the CPU does not receive a

response, it eliminates the receiver ports as a forwarding destination for this group.

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 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

Multicast VLAN Registration Example

Cisco router

Blade Switch

RP = Receiver Port

SP = Source Port

Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide

Understanding Multicast VLAN Registration

Note: All source ports belong to

the multicast VLAN.

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