Leaving A Multicast Group - Cisco Catalyst 3120 Software Manual

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Configuring IGMP Snooping and MVR

If another blade server (for example, Blade Server 4) sends an unsolicited IGMP join message for the

the forwarding table as shown in

messages only to the CPU, the message is not flooded to other ports on the switch. Any known multicast

traffic is forwarded to the group and not to the CPU.

Destination Address

Leaving a Multicast Group

The router sends periodic multicast general queries, and the switch forwards these queries through all

ports in the VLAN. Interested blade servers respond to the queries. If at least one blade server in the

VLAN wishes to receive multicast traffic, the router continues forwarding the multicast traffic to the

VLAN. The switch forwards multicast group traffic only to those blade servers listed in the forwarding

table for that IP multicast group maintained by IGMP snooping.

When blade servers want to leave a multicast group, they can silently leave, or they can send a leave

message. When the switch receives a leave message from a blade server, it sends a group-specific query

to learn if any other devices connected to that interface are interested in traffic for the specific multicast

group. The switch then updates the forwarding table for that MAC group so that only those blade servers

interested in receiving multicast traffic for the group are listed in the forwarding table. If the router

receives no reports from a VLAN, it removes the group for the VLAN from its IGMP cache.

23-2), the CPU receives that message and adds the port number of Blade Server 4 to

Second Host Joining a Multicast Group

Switching engine

Updated IGMP Snooping Forwarding Table

23-2. Note that because the forwarding table directs IGMP

Type of Packet

Cisco Catalyst Blade Switch 3120 for HP Software Configuration Guide

Understanding IGMP Snooping

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