Configuring IGMP Snooping

To support selective Multicast forwarding (IPv4), Bridge Multicast filtering must be enabled (in the Properties page), and IGMP Snooping must be enabled globally and for each relevant VLAN (in the IGMP Snooping page).

Additional Information

By default, a Layer 2 device forwards Multicast frames to all ports of the relevant VLAN, essentially treating the frame as if it were a Broadcast. With IGMP Snooping the device forwards Multicast frames to ports that have registered Multicast clients.

NOTE     The device supports IGMP Snooping only on static VLANs. It does not support IGMP Snooping on dynamic VLANs.

When IGMP Snooping is enabled globally or on a VLAN, all IGMP packets are forwarded to the CPU. The CPU analyzes the incoming packets, and determines the following:

• Which ports are asking to join which Multicast groups on what VLAN.
• Which ports are connected to Multicast routers (Mrouters) that are generating IGMP queries.
• Which ports are receiving PIM, DVMRP, or IGMP query protocols.

These are displayed on the IGMP Snooping page.

Ports, asking to join a specific Multicast group, issue an IGMP report that specifies which group(s) the host wants to join. This results in the creation of a forwarding entry in the Multicast Forwarding Data Base.

The IGMP Snooping Querier is used to support a Layer 2 Multicast domain of snooping switches in the absence of a Multicast router. For example, where Multicast content is provided by a local server, but the router (if one exists) on that network does not support Multicast.

The speed of IGMP Querier activity must be aligned with the IGMP-snooping- enabled switches. Queries must be sent at a rate that is aligned to the snooping table aging time. If queries are sent at a rate lower than the aging time, the subscriber cannot receive the Multicast packets. This is performed in the IGMP Snooping Edit page.

To enable IGMP Snooping and identify the device as an IGMP Snooping Querier on a VLAN:

1. Click Multicast > IGMP Snooping.
2. Enable or disable the IGMP Snooping status.

When IGMP Snooping is enabled globally, the device monitoring network traffic can determine which hosts have requested to receive Multicast traffic.

The device only performs IGMP Snooping if both IGMP snooping and Bridge Multicast filtering are enabled.

3. Select a VLAN, and click Edit.

There can be only one IGMP Querier in a network. The device supports standards-based IGMP Querier election. Some of the values of the operational parameters of this table are sent by the elected querier. The other values are derived from the device.

4. Enter the parameters.
• VLAN ID—Select the VLAN ID on which IGMP snooping is defined.
• IGMP Snooping Status—Enable or disable the monitoring of network traffic for the selected VLAN.
• Operational IGMP Snooping Status—Displays the current status of the IGMP Snooping for the selected VLAN.
• MRouter Ports Auto Learn—Enable or disable auto learning of the ports to which the Mrouter is connected.
• Query Robustness—Enter the Robustness Variable value to be used if this device is the elected querier.
• Operational Query Robustness—Displays the robustness variable sent by the elected querier.
• Query Interval—Enter the interval between the General Queries to be used if this device is the elected querier.
• Operational Query Interval—The time interval in seconds between General Queries sent by the elected querier.
• Query Max Response Interval—Enter the delay used to calculate the Maximum Response Code inserted into the periodic General Queries.
• Operational Query Max Response Interval—Displays the Query Max Response Interval included in the General Queries sent by the elected querier.
• Last Member Query Counter—Enter the number of IGMP Group-Specific Queries sent before the device assumes there are no more members for the group, if the device is the elected querier.
• Operational Last Member Query Counter—Displays the operational value of the Last Member Query Counter.
• Last Member Query Interval—Enter the Maximum Response Delay to be used if the device cannot read Max Response Time value from group-specific queries sent by the elected querier.
• Operational Last Member Query Interval—Displays the Last Member Query Interval sent by the elected querier.
• Immediate Leave—Enable Immediate Leave to decrease the time it takes to block a Multicast stream sent to a member port when an IGMP Group Leave message is received on that port.
• IGMP Querier Status—Enable or disable the IGMP Querier.
• Administrative Querier Source IP Address—Select the source IP address of the IGMP Querier. This can be the IP address of the VLAN or it can be the management IP address.
• Operational Querier Source IP Address—Displays the source IP address of the elected querier.
• IGMP Querier Version—Select the IGMP version used if the device becomes the elected querier. Select IGMPv3 if there are switches and/or Multicast routers in the VLAN that perform source-specific IP Multicast forwarding.
5. Click Apply. The Running Configuration file is updated.