Using Mvr In A Multicast Television Application - Cisco Catalyst 3120 Software Manual

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Configuring IGMP Snooping and MVR

Using MVR in a Multicast Television Application

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

dynamically register for streams of multicast traffic in the multicast VLAN on the Layer 3 device. The

access layer blade switch 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

Multicast VLAN Registration Example

RP = Receiver Port

SP = Source Port

Cisco router

Blade Switch

Note: All source ports belong to

the multicast VLAN.

Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide

Understanding Multicast VLAN Registration

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